Alan G. Dexter
Extension Sugarbeet Specialist
Sugarbeet is a low growing crop and many weeds grow taller than sugarbeet. Weeds that become taller than the crop will cause greater yield loss than weeds that do not overtop the crop canopy so yield losses in sugarbeet due to weed competition can be large. Also, weed losses from direct competition are only part of the problems that may be caused by weeds. Weeds may also a) cause harvest problems, b) reduce the quality of the harvested product, c) produce seed that increases future weed problems, d) act as co-hosts for insects and diseases, e) increase tillage needed for weed control, and f) reduce animal and human health.
Competition research conducted in eastern North Dakota and Minnesota found that a 5% loss in extractable sucrose per acre was caused by 25 redroot pigweed plants per 100 feet of row or by 30 wild oat plants per 100 feet of row averaged over 10 experiments or 11 experiments, respectively (Figure 1).
Competition research in Colorado by Ed Schweizer found that only one kochia plant in 200 feet of row would cause a 5% loss in sugarbeet yield. Weed species differ in their competitive ability with larger, taller weeds causing more loss per plant than smaller, shorter weeds. Weeds also vary in competitive ability in different environments since one environment may favor the weed more than the crop while another environment may favor the crop more than the weed. For example, redroot pigweed at a density of three plants per meter of row caused a 44% sugarbeet yield loss in one experiment in the Red River Valley, while the same density of redroot pigweed caused only a 1% yield loss in a different experiment. The more competitive redroot pigweed emerged five days before the sugarbeet with a May 10 planting date while the less competitive redroot pigweed emerged 7 days after the sugarbeet with an April 28 planting date. Also, sugarbeet with a uniform distribution of plants will be more competitive with weeds than sugarbeet having gaps in the stand. Weeds that survive herbicide treatment generally will be less competitive than weeds not treated with herbicide. All of these observations lead to the conclusion that sugarbeet yield loss can not be accurately predicted from weed density alone.
Richard Evans conducted competition research in sugarbeet in eastern North Dakota and Minnesota as his PhD thesis research at North Dakota State University. The thesis was completed in 1983. He developed equations to predict sugarbeet yield loss from redroot pigweed and wild oat competition.
1. Predictive equation for redroot pigweed.
Extractable sucrose in kg/ha = 7255 - D (159.5) + D2 (29.2) - C (147.2) - CD
(16.7) + P (206.5)
D = redroot pigweed density in plants per meter of row.
C = Average of maximum and minimum daily soil temperatures for 7 days in centigrade taken
10 cm under grass sod.
P = Total precipitation for 7 days in cm.
All measurements should be taken during the fourth week after planting.
2. Predictive equation for wild oat.
Extractable sucrose in kg/ha = 7051 - D (412.7) + D2 (20.9) - C (129.3) + CD
(5.6) + P (142.8)
D = wild oat density in plants per meter of row.
C = Average of maximum and minimum daily soil temperatures for 7 days in centigrade taken
10 cm under grass sod.
P = Total precipitation for 7 days in cm.
The equations must be worked twice to obtain an estimate of the yield loss that would be caused by weed competition. Use the equations once assuming zero weeds and once using the actual weed population. The difference between the two yield estimates is the estimated loss from weed competition. Calculate a percentage loss and then apply this percentage to the estimated potential yield of the field in question.
Weeds should be controlled within four weeks after sugarbeet emergence in order to avoid yield loss from weed competition. These equations were developed to be used early in the growing season, i.e. four weeks after planting, to assist with weed control decisions that must be made by four weeks after sugarbeet emergence. The environmental conditions the remainder of the growing season can have a large influence on relative weed competition and predictive equations that include environmental measurements two months or more into the growing season would be more accurate. However, weed control decisions must be made early so a useful predictive equation only can utilize information available in the early part of the season. In this research, using soil temperatures and precipitation for six weeks after planting in the equations did not improve the ability to predict yield loss as compared to using soil temperatures and precipitation only from the fourth week after planting.
The equations were developed using the following assumptions:
The equations will not provide an exact estimate of sugarbeet yield loss for all situations because many variables (such as environment for the rest of the growing season) are not included in the equations and because the listed assumptions will not be true for all fields. However, the equations will give a more accurate estimate of sugarbeet yield loss from redroot pigweed and wild oat competition than from weed density alone. Figure I provides yield loss data averaged over several experiments conducted in eastern North Dakota and Minnesota for reference purposes but please remember that the relative competitive ability of the weeds varied considerably from experiment to experiment.
Sugarbeet growers should and usually do consider that a) sugarbeet is a high-value crop, b) weeds can cause severe sugarbeet yield loss, c) weeds produce seeds that cause future problems and d) weeds cause losses and problems not directly related to competition. After due consideration, sugarbeet growers can not be faulted for concluding that the only good weed is a dead weed. Most sugarbeet growers are willing to spend extensive time and resources attempting to obtain total weed control. Every situation is different but often total weed control can be justified, even if the cost of control of the last few weeds may be greater than the value of the yield losses that would be caused by the weeds. This is especially true in fields with low weed seed densities where a few weeds producing seed will significantly increase future weed problems. Control of the last few weeds is harder to justify in a field with a large existing populations of weed seed although near total weed control is needed in order to significantly reduce the levels of weed seed in the soil.
THE WEED CONTROL SUGGESTIONS are based on Federal label clearances and on information obtained from Agricultural Experiment Stations and the Research Report of the North Central Weed Science Society. CAUTION: The weed control suggestions in this guide are based on the assumption that all herbicides mentioned in this guide have and will continue to have a registered label with the Environmental Protection Agency. Herbicide labels should be checked for registered uses on sugarbeet prior to application. Portions of this section are taken from the North Dakota State University Agricultural Weed Control Guide, Circular W-253 so some non-sugarbeet herbicides are included in the text.
USE CHEMICALS ONLY AS RECOMMENDED ON THE LABEL.
RATES ARE BASED on broadcast application and are expressed as active ingredient or acid equivalent, and as the amount of commercial product. Commercial formulations of the same herbicide may vary in amount of active ingredient. For example, Eptam is available in a liquid formulation which has seven pounds of active ingredient per gallon or in a granular formulation which has 20% active ingredient. A desired application rate of 2 lb/A would require 2.3 pints/A of the liquid formulation or 10 lb/A of the granules.
RAINFALL shortly after application often reduces weed control from postemergence applications because the herbicide is washed off the leaves before absorption is complete. Herbicides vary in rate of absorption and in ease of being washed from leaves and therefore vary in response to rainfall. The amount and intensity of rainfall also influence the washing of herbicides from leaves. The approximate time between application and rainfall needed for maximum weed control from several herbicides follows: Assure II--1 hour; Betamix6 hours; Betanex6 hours; Betamix Progress--6 hours; Roundup6 hours; Select or Prism--1 hour; Stinger--6 hours; Poast or Ultima 160--1 hour; UpBeet--6 hours.
SPRAY ADDITIVES: Postemergence herbicide effectiveness is dependent upon spray droplet retention and herbicide absorption by weed foliage. Adjuvants and spray quality influence postemergence herbicide efficacy. Adjuvants are not important to preemergence herbicides because retention and absorption by foliage does not occur. The advent of postemergence herbicides for weed control in corn and soybean has increased the interest in adjuvants.
Spray additives consist of oils, surfactants, and fertilizers. The most effective additive will vary with each herbicide and the need for an additive will vary with environment, weeds present, and herbicide used. Additives should be used only when indicated on the herbicide label as they may increase injury to crops or reduce weed control.
Oils generally are used at 1% v/v (1 gal/100 gal of spray solution) or at 1 to 2 pt/A depending upon herbicide and oil. Oil additives function to increase herbicide absorption and spray retention. Oil adjuvants are petroleum, vegetable, or methylated vegetable oils plus an emulsifier for dispersion in water spray carriers. The emulsifier, the oil class (petroleum, vegetable, etc.) and the specific type of oil in a class all influence effectiveness of a given oil adjuvant. Methylated vegetable oils have been especially effective with Poast and Accent, but generally are equal or better than the other oil classes with all herbicides. However, Cobra is more effective when applied with petroleum then methylated vegetable oil. Vegetable oils usually are equal to petroleum oils, except less effective with Assure. The above comparison may differ depending on the specific adjuvant product. Betanex or Betamix plus oil adjuvant usually gives more sugarbeet injury than Betanex or Betamix alone.
Surfactants are used at 0.12 to 0.5% v/v (1 to 4 pt/100 gal of spray solution). Surfactant rate depends on the amount of active ingredient in the surfactant and other factors such as species and herbicides. The main function of a surfactant is to increase the plant spray retention, but surfactants also function in herbicide absorption. When a range of surfactant rates is given, the high rate is for use with low rates of the herbicide, drought stress, tolerant weeds, or when the surfactant contains a low (less than 50%) percentage active ingredient. Surfactants vary widely in their chemical composition and in their effect on spray retention and herbicide absorption. Effectiveness of a given surfactant will also depend upon the herbicide and its formulation. Information on surfactant effectiveness with a herbicide requires field testing and can not be predicted from surface tension or droplet spread on wax surface. Betanex or Betamix plus surfactant often causes more sugarbeet injury than Betanex or Betamix alone.
Fertilizers containing ammonium nitrogen have increased the effectiveness of Carbyne, Blazer, glyphosate, bentazon, Accent, Pursuit, and Poast. Fertilizer applied with herbicides may reduce weed control or cause crop injury. Fertilizers should be used with herbicides only as indicated on the label or where experience has proven acceptability. Fertilizers plus Betanex or Betamix often cause excessive sugarbeet injury.
Ammonium sulfate (AMS) at 17 lb per 100 gal spray volume (2%) has enhanced weed control with glyphosate. Enhancement of glyphosate is most pronounced when spray water contains relatively large quantities of certain ions, such as calcium, sodium, and magnesium. AMS may contain contaminants which may not dissolve and then plug nozzles. AMS should be dissolved in a small amount of water and filtered to prevent nozzle plugging. Commercial solutions of AMS are available. AMS at 2% is adequate to overcome severe salt antagonism. AMS at 0.5% has adequately overcome antagonism of glyphosate from 300 ppm calcium. Ammonium ions also are involved in herbicide absorption and have enhanced phytotoxicity of many herbicides in the absence of salts in the spray carrier. The enhancement of herbicides by nitrogen compounds appears most pronounced to certain species (velvetleaf, sunflower).
AMS enhances phytotoxicity and overcomes antagonism from salts of Poast, glyphosate, and 2,4-D amine and 28% nitrogen (UAN) is effective in enhancing weed control from many POST herbicides and overcoming sodium but not calcium antagonism of glyphosate. Sodium bicarbonate antagonism of Poast is overcome by 28% UAN, ammonium nitrate, and AMS.
AMS or 28% UAN does not preclude the need for a surfactant. Many adjuvants are available to enhance herbicide action, but information on their effectiveness is limited. The precise salt concentration in water which causes a visible loss in weed control is difficult to establish because weed control also is influenced by many other factors. Thus, comparisons of adjuvants should be made at marginal control levels to determine the effectiveness of adjuvants for specific herbicides, sprays, water and weeds. Effective adjuvants may allow use of herbicides at reduced rates or provide consistent results with adverse conditions. However, use of rates less than the label recommendation exempts herbicide manufacturers from liability for nonperformance.
Minerals, clay, and organic matter in spray carrier water can reduce the effectiveness of herbicides. Clay inactivates paraquat and glyphosate, organic matter inactivates many herbicides, and minerals of various types can inactivate 2,4-D amine, MCPA amine, Poast, Ultima 160, glyphosate, and dicamba.
Water in many parts of the United States is high in sodium bicarbonate which reduces the effectiveness of 2,4-D and MCPA amines (not esters), Poast, Ultima 160, glyphosate, and dicamba. Water samples with 1600 ppm sodium bicarbonate have been observed, but antagonism of the above herbicides was noticeable at or above 300 ppm. The antagonism is related to the salt concentration. At low salt levels, loss in weed control may not be noticeable under normal environmental conditions. However, the antagonism from low salt levels will cause inadequate weed control when weed control is marginal because of drought or partially susceptible weeds.
High salt levels in spray water can reduce weed control in nearly all situations. Calcium and, to a lesser degree, magnesium are antagonistic to 2,4-D and MCPA amine, dicamba, and glyphosate. Calcium antagonism may become noticeable at 150 ppm. Sulfate ions in the solution have reduced the antagonism from calcium and magnesium, but the sulfate concentration must be three times the calcium concentration to overcome antagonism. The sulfate that occurs naturally in water can be disregarded. The amount of AMS needed to overcome antagonistic ions can be determined as follows: AMS (lb/100 gal water) = 0.005 sodium [ppm] + 0.002 potassium [ppm] + 0.009 calcium [ppm] + 0.014 magnesium [ppm].
An analysis of spray water sources will provide a guide for determining possible effects on herbicide efficacy. AMS at 2% as indicated on many labels (17 lb/100 gallons spray) will overcome the antagonism from the highest calcium and/or sodium concentrations in North Dakota and Minnesota waters for glyphosate, Ultima 160, Poast, 2,4-D amine, MCPA amine, and dicamba. However, AMS at 1% is adequate for most North Dakota and Minnesota waters. Iron also is antagonistic to many herbicides, but usually is not abundant in North Dakota and Minnesota waters.
Water often contains a combination of sodium, calcium, and magnesium, and these cations generally are additive in the antagonism of herbicides. Many adjuvants are marketed to modify spray water pH, but low pH does not appear essential to the action of most herbicides. AMS, granular or liquid, and 28% UAN fertilizer help overcome antagonistic salts in spray carrier water. The 28% UAN fertilizer overcomes mineral antagonism of most herbicides, but not glyphosate. Research results with amounts of 28% UAN fertilizer is limited, but 4 gal/100 gal of spray has generally been adequate.
The AMS and 28% UAN adjuvants have enhanced herbicide control of certain weeds even in water without salts. This is especially true for glyphosate, sulfonylureas (Ally, Amber, Express, Harmony Extra, and Pinnacle), Blazer, and bentazon. However, AMS, 28% UAN, or other adjuvants should be used with caution as their benefit often is limited to specific herbicides or weeds and may be antagonistic to other herbicides or weeds.
Movement of herbicides off target is a problem in North Dakota each year as herbicides move from target fields into nontarget areas containing crops or other plant species susceptible to the herbicide. Spray drift and injury to plants are affected by several factors.
a) Wind velocity and direction: To minimize spray drift injury, wind direction should be away from susceptible plants during herbicide application. The wind velocity should be less than 10 miles per hour. However, drift can occur even with lower wind velocities, especially when air is vertically stable. Normally, air near the soil surface is warmer than higher air. Warm air rises and cold air sinks which causes vertical mixing of air and dissipation of spray droplets. Vertically stable air (temperature inversion) occurs when air near the soil surface is cooler or similar in temperature to higher air. Small spray droplets can be suspended in stable air, move laterally in a light wind, and impact plants two miles or more downwind. Herbicide application should be avoided when vertically stable air conditions occur. These conditions can be identified by observing smoke bombs or dust from a gravel road. Fog also would indicate vertically stable air.
b) Distance between nozzle and target (boom height): droplets should be released as close to the target as possible while maintaining uniform spray coverage. Less distance means less time to fall and therefore less potential for drift to occur.
c) Herbicide formulation: All herbicides can drift as spray droplets but some herbicides are sufficiently volatile to cause plant injury from vapor or fume drift. Herbicide volatility and consequent risk of damage to susceptible plants increases with increasing temperature. The so-called high volatile esters of 2,4-D or MCPA may produce damaging vapors at temperatures as low 40 F while low volatile esters may produce damaging vapors between 70 to 90 F. Amine formulations are essentially non-volatile even at high temperatures. Temperature on the soil surface often is several degrees warmer than air temperature. Thus an applied low volatile ester could be exposed to temperatures high enough to cause damaging vapor formation even when the air temperature is below 70 F. Dicamba (Banvel) also is volatile and can drift as droplets or vapor. Herbicide vapor drifts further and over a longer time than spray droplets. A wind blowing away from susceptible plants during application will prevent damage from droplet drift but a later wind shift towards the susceptible plants could move damaging vapors to the plants. Thus, to minimize the risk of drift injury, herbicides such as 2,4-D esters, MCPA esters, and dicamba with high potential to form damaging vapors should not be used near susceptible plants.
d) Drift control: Spray drift can be reduced by increasing droplet size since a wind will move large droplets less than small droplets. Droplet size can be increased by reducing spray pressure, increasing nozzle orifice size, special drift reduction nozzles, additives that increase spray viscosity, and rearward nozzle orientation on aircraft.
Techniques which increase droplet size may reduce weed control from herbicides that require small droplets for optimum effectiveness, such as Carbyne (barban), Fusilade 2000 (fluazifop-P), Option II (fenoxaprop), Assure II (quizalofop-P), Betanex (desmedipham), Betamix (desmedipham + phenmedipham), Poast or Ultima 160 (sethoxydim), bentazon, and Buctril (bromoxynil). Weed control from readily translocated herbicides is affected little by droplet size within a normal range, for example 2,4-D, MCPA, Banvel (dicamba), Stinger (cloypralid), and Tordon (picloram). Droplet size has minimal effect on glyphosate but glyphosate is partially inactivated by increased water volume so spray recommendations on the label should be followed.
e) Shields around spray nozzles or spray booms will partially protect spray droplets from wind and reduce spray drift. Small plastic cones that fit around individual nozzles reduce drift by approximately 25 to 50% and spray shields which enclose the entire boom reduce drift by approximately 50 to 85%. Spray shields give a greater reduction in drift when winds are low and droplets are relatively large. Therefore, spray shields should not be used as a substitute for other drift control techniques but should be used as a supplement to all other applicable methods of drift reduction.
f) Injury from herbicide drift: Damaging drift from other crops into sugarbeet is primarily a problem with 2,4D, MCPA, Banvel, Assert, Express, Gramoxone Extra, Harmony Extra, Pinnacle, Pursuit, Roundup, and Tordon in North Dakota and Minnesota. The primary risk of damaging drift from sugarbeet to other crops is with postemergence grass control herbicide drift into small grains or corn. Other herbicides may drift but generally do not cause significant damage or are not used commonly near sugarbeet. All herbicides may drift and cause significant damage to susceptible nontarget plants, so caution must be observed with all herbicide applications.
Crop injury may occur from a contaminated sprayer. The risk of damage is greatest when spraying crops highly susceptible to the previous herbicide and when the previous herbicide is very active in small amounts. Rinsing with water is not adequate to remove all herbicides. Some herbicides have remained tightly adsorbed in sprayers through water rinsing and even through several tank-loads of other herbicides. Then when a tank-load of solution including an oil adjuvant or nitrogen solution was put in the sprayer, the herbicide was desorbed, moved into the spray solution, and damaged susceptible crops. Highly active herbicides that have been difficult to wash from sprayers and have caused crop injury include dicamba (Banvel) and the ALS inhibitor herbicides (Harmony Extra, Express, Pinnacle, Pursuit, Ally, Accent, Amber, Beacon and other related herbicides).
Herbicides which are difficult to remove from sprayers are thought to be attaching to residues remaining from spray solutions that deposit in a sprayer. The herbicide must be desorbed from the residue or the residue removed in a cleaning process so the herbicide can be removed from the sprayer. Sprayer cleanout procedures are given on many herbicide labels and the procedure on the label should be followed for specific herbicides. The following procedure is given as an illustration of a thorough sprayer cleanup procedure that would be effective for most herbicides.
Step 1. Drain tank and thoroughly rinse interior surfaces of tank with clean water. Spray rinse water through the spray boom. Sufficient rinse water should be used for 5 minutes or more of spraying through the boom.
Step 2. Fill the sprayer tank with clean water and add a cleaning solution (many labels provide recommended cleaning solutions). Fill the boom, hoses, and nozzles and allow the agitator to operate for 15 minutes.
Step 3. Allow the sprayer to sit for 8 hours while full of cleaning solution. The cleaning solution should stay in the sprayer for 8 hours so that the herbicide can be fully desorbed from the residues inside the sprayer.
Step 4. Spray the cleaning solution out through the booms.
Step 5. Remove nozzles, screens, and filters and clean thoroughly. Rinse the sprayer to remove cleaning solution and spray rinsate through the booms.
Common types of cleaning solutions are chlorine bleach, ammonia, and commercially formulated tank cleaners. Chlorine lowers the pH of the solution which speeds the degradation of some herbicides. Ammonia increases the pH of the solution which increases the solubility of some herbicides. Commercially formulated tank cleaners generally raise pH and act as detergents to assist in removal of herbicides.
Read the herbicide label for recommended tank cleaning solutions and procedures. WARNING: Never mix chlorine bleach and ammonia as a dangerous and irritating gas will be released.
Sprayers should be cleaned as soon as possible after use to prevent the deposit of dried spray residues. If a sprayer will remain empty over night without cleaning, fill the tank with water to prevent dried spray deposits from forming. A sprayer kept clean is essential to prevention of damage from herbicide contamination.
Groundwater contamination with pesticides is a growing public concern. Pesticides can contaminate groundwater by movement from small areas contaminated through factors such as spills, rinsing spray cans, rinsing tanks, and back-siphoning, (point source) or by movement of pesticides used according to their label on relatively large land areas (non-point source). Point source contamination probably accounts for most groundwater contamination problems and can be minimized by using the following precautions:
Non-point source groundwater contamination occurs over a broad area as a result of labelled pesticide uses. Groundwater contamination can occur as the chemical is leached by water through the soil profile. The potential for non-point source pollution of groundwater with a herbicide depends on soil type, irrigation or precipitation, depth of groundwater, herbicide application rate and frequency, and herbicide mobility. Non-point pollution of groundwater can be minimized by using the following practices:
Weed biotypes resistant to a herbicide occur from repeated use of a selective herbicide that eliminates susceptible weed species and allows tolerant weed species to increase in the absence of competition from the susceptible plant species. Likewise, individual plant species also may have biotypes in the population that vary in susceptibility to certain herbicides. Weed species that are very susceptible to certain herbicides may contain a small percentage of plants which are tolerant or resistant to those herbicides. Repeated exposure of a weed population to a herbicide or other herbicides with the same mode of action may result in a rapid buildup of biotypes resistant to that class of herbicides. Resistant biotypes dominate the population over time due to this selection pressure. The time required for buildup of a herbicide resistant weed population depends on many factors including: effectiveness of herbicides, frequency of herbicide use, genetic variability within the species, frequency of the resistant biotype in the population, beginning level of resistance, and characteristics of the weed, including fitness or ability of the biotype to compete with other weeds both within and outside the species.
Within North Dakota since the mid 1980s, three weed species have developed significant resistance to herbicides:
Sulfonylurea Resistant Kochia. According to a survey taken in 1993, sulfonylurea (SU) resistant kochia is found primarily in regions of North Dakota where Glean herbicide was extensively used. This area is along the northern, western, and southwestern sections of the state. However, resistant biotypes were found scattered throughout the entire state. Extensive use of Glean along with its long residual activity is believed the main factor contributing to the expression of SU resistant kochia biotypes. Common use of other SU herbicides like Ally, Amber, Express and Harmony Extra may also contribute to this development. SU resistant kochia will be resistant to UpBeet, an SU herbicide registered for use on sugarbeet.
SU resistant kochia biotypes are also resistant to the recently introduced herbicide Broadstrike. This herbicide is of a different chemistry but has the same mode of action as SU herbicides. Pursuit is also of a different chemistry than SU herbicides and Broadstrike. However, Pursuit has the same mode of action but acts on a different site on the ALS enzyme than where Broadstrike and the SU herbicides act. Research indicates that Pursuit can control most SU resistant kochia biotypes but repeated exposure of SU and Broadstrike resistant biotypes to Pursuit may result in kochia biotypes resistant to all three chemistries: SU herbicides, Broadstrike, and Pursuit. This demonstrates the need to rotate herbicides with different modes of action as a long-term weed control strategy is planned.
Growth Regulator Resistant Kochia. From the survey conducted in 1993, SU resistant kochia biotypes have been discovered that are also resistant to growth regulator type herbicides. Growth regulator type herbicides control a broad spectrum of weeds, are inexpensive, and are common tank-mix partners with other herbicides. These factors contribute to the wide use of growth regulator type herbicides. To prevent further buildup of cross and multiple resistant kochia biotypes, the current recommendations of tankmixing SU herbicides with growth regulator type herbicides must be supplemented with additional herbicide rotational strategies. Rotate often with herbicides having a different mode of action other than SU or growth regulator type herbicides. If using an SU herbicide, tank-mix with a non-growth regulator type herbicide (for example, bromoxynil) even though cost per acre will higher.
Trifluralin Resistant Green Foxtail is found mainly in the central and eastern portion of North Dakota where consecutive, year after year use of trifluralin is common. Similar to SU resistance, expression of green foxtail resistance was caused by successive, year after year use of trifluralin in small grain crops, row crops, and fallow. A common practice in the central part of the state is to grow continuous small grains, or a small grain/fallow rotation, or a small grain/sunflower rotation. For these cropping rotations, trifluralin can be used every year. Also, trifluralin can be applied at high rates in broadleaf crops with small grains seeded the next year. Trifluralin carryover into the small grain crop would reduce green foxtail infestations but not injure the small grain. Either continuous application or high rates resulted in a high selection pressure and expression of trifluralin resistant green foxtail.
Poast, Hoelon and fenoxaprop resistant wild oat is found within the Red River Valley of North Dakota and Minnesota. Development of resistance can be attributed to extensive use of Hoelon or fenoxaprop premix products (Tiller and Cheyenne) for wild oat control in small grains and yearly single and/or multiple applications of Poast in sugarbeet.
Resistant kochia can be expressed after 3 to 5 applications of an effective herbicide. Resistant green foxtail and wild oat can be expressed after 8 to 12 applications of an effective herbicide.
Other resistant weed situations may continue to develop in North Dakota. Many weeds have developed resistance to other herbicides, classes of herbicides (cross resistance), and to more than one class of herbicide (multiple resistance) in areas other than North Dakota. For example, in Canada, green foxtail has developed resistance to trifluralin and Hoelon. In Montana and Canada, wild oat has developed resistance to Far-Go and Avenge.
In summary, herbicide resistant weeds are most likely to develop by using: 1) Herbicides that act on a single site of action, 2) Herbicides applied multiple times during the growing season or with a long residual herbicide, 3) Herbicides used for several consecutive growing seasons or repeated application of herbicides with the same mode of action to the same or different crops, and 4) Herbicides used as "stand alone" products, without other weed control options (e.g. cultivation) utilized.
Weeds species most likely to develop resistance are genetically variable and have a rapid life cycle with short seed dormancy such as kochia and Russian thistle. Populations of kochia, Russian thistle, and prickly lettuce have developed resistance to sulfonylurea herbicides in several areas other than North Dakota. Wild mustard has developed resistance to the entire growth regulator type herbicide complex and the SU chemistry in Canada. Green foxtail has developed resistance to trifluralin and ACCase herbicides in Canada. Giant foxtail and large crabgrass have developed resistance to ACCase inhibitor herbicides.
The following list of strategies to avoid herbicide resistance problems was drafted from suggestions provided by members of the NCWSS Herbicide Resistant Weed Committee. These strategies should be equally effective for avoiding problems with both herbicide tolerant weed species and herbicide resistant weed biotypes. However, no single strategy is likely to be totally effective. These strategies must be implemented in carefully selected combinations by each herbicide user if herbicide resistant weed problems are to be avoided.
Herbicide Classification and Mode of Action for Resistant Weed
Management
Alternative Herbicide Options to Avoid and/or Manage Resistant
Weeds in ND
PREEMERGENCE HERBICIDES: Good weed control with preemergence herbicides depends on many factors including rainfall after application, soil moisture, soil temperature, soil type, and weed species. For these reasons, preemergence herbicides applied to the soil surface sometimes fail to give satisfactory weed control. Herbicides which are incorporated into the soil usually require less rainfall after application for effective weed control than unincorporated herbicides. Weeds emerging through a preemergence herbicide treatment may be controlled by rotary hoeing or harrowing without reducing the effect of the herbicide unless the harrow or rotary hoe removes the herbicide from a treated band.
PESTICIDE COMBINATIONS: The recommended sequence of addition of formulations for tank mixes is a) water, b) wettable powders or dry flowables plus agitation, c) liquid flowables, d) emulsifiable concentrates, and e) solutions. Compatibility testing as described in the herbicide + liquid fertilizer section can be used to determine if tank mixes of pesticides will form a uniform mixture in the spray tank. The effect of postemergence herbicides often is increased when applied to areas already treated with a preemergence or preplant herbicide. Combinations of certain herbicides may give better weed control than use of the individual herbicide alone. However, loss of weed control or increased crop damage may result from the use of certain other herbicides in combination. Herbicide combinations should be used with caution until experience or research has shown that the combination is effective and safe.
Several herbicide combinations with other pesticides have been shown to increase crop injury compared to either pesticide applied alone. For example, sugarbeet injury has increased when tin fungicides have been combined with Poast + oil or when Betamix/Betamix has been combined with Lorsban. Efficacy data on herbicidepesticide mixtures are limited because of the number of potential combinations. Nonregistered tankmixtures should be used with caution until experience or research has shown that the combination is effective and safe. See the 1987 Sugarbeet Research and Extension Reports, pages 7483 for results of experiments with combinations of sugarbeet herbicides with other agrichemicals.
Agricultural pesticides that are tank mixed are often registered for use as a mixture by the Environmental Protection Agency. Nonregistered tank mixes may be applied if all pesticides in the mixture are registered by the Environmental Protection Agency on the crop being treated. However, the user must assume liability for crop injury, inadequate weed control and illegal residues if the combination is not a labelled tank mixture.
INCORPORATION OF HERBICIDES: Many herbicides applied before crop and weed emergence need to be incorporated to give optimum weed control. Included in this group are RoNeet and Eptam. Weed control from Nortron and Pyramin generally is improved by incorporation. RoNeet and Eptam should be incorporated immediately after application regardless of whether the liquid or granular formulation is used. Nortron and Pyramin may be used preemergence but incorporation usually improves weed control, especially on finetextured soils or with limited rainfall after application. Incorporation may reduce weed control if heavy rains follow application and incorporation may increase sugarbeet injury compared to surface application. Experience indicates that lack of rainfall is more common than excess rainfall following planting.
An estimate of the efficiency of an incorporating tool can be obtained by operating the tool through flour or lime which has been spread thickly over the soil. A thorough incorporation should cover most of the flour or lime and give uniform mixing through the soil. Several tillage tools have been used successfully for the incorporation of herbicides. Some herbicides require more thorough incorporation than others and the incorporation method should be matched to the herbicide.
RoNeet and Eptam require a thorough incorporation and should be incorporated by one of the following methods or a method which will incorporate similarly.
a) A tandem disk should be set at a depth of 4 to 6 inches for Eptam or RoNeet. Operating speed should be 4 to 6 mph. Tandem disks with disk blades spaced 8 inches or less and disk blade diameter of 20 inches or less have given good herbicide incorporation. Larger disks often give streaked incorporation and poor weed control.
b) Field cultivators of various types may be used. These should have overlapping sweep shovels with at least three rows of gangs and the operating depth should be 4 to 6 inches for Eptam and RoNeet. A harrow should follow the field cultivator. The operating speed necessary to achieve a satisfactory incorporation will vary somewhat depending on the type of field cultivator but the speed usually will be 6 to 8 mph.
c) Field cultivators with Danish tines plus rolling crumblers behind have given good herbicide incorporation. These tools should be operated 4 inches deep and at 7 to 8 mph or faster. Adequate incorporation with one pass may be possible with these tools if soil conditions are ideal for herbicide incorporation. However, a second incorporation maybe good insurance against poor weed control.
d) Power driven rototillertype equipment will give adequate incorporation when set to operate at a depth of 2 to 4 inches at the manufacturer's recommended ground speed.
A single incorporation with a power driven rototiller is sufficient for RoNeet or Eptam. However, a second tillage at right angles to the initial incorporation should be done if the disk or field cultivator is used. The second incorporation has two purposes: a) Most of the herbicide left on the surface after the first incorporation will be mixed into the soil with the second tillage, and b) the second tillage will give more uniform distribution of the herbicide in the soil which will improve weed control and may reduce crop injury. Nortron and Pyramin do not require deep incorporation. A tillage tool operating at a minimum depth of 2 inches will give adequate incorporation if the tool mixes the herbicide uniformly through the soil.
THE SOIL ORGANIC MATTER TEST: Certain herbicides are partially adsorbed and inactivated by soil organic matter, so knowledge of the organic matter level will serve as a guide in selecting an effective herbicide and an effective herbicide rate. Herbicides such as RoNeet, Eptam, and Pyramin require higher rates to give good weed control in high organic matter soils. On the other hand, crop safety may be marginal on low organic matter soils. Herbicides also are adsorbed to the clay fraction in a soil, so clay content affects herbicide performance. However, organic matter level generally affects herbicide performance more than clay content.
Sugarbeet has marginal tolerance to Eptam so the rate must be adjusted on various soils to give good weed control without crop injury. The following discussion on selecting an Eptam rate only gives guidelines. Other factors such as method of incorporation also affect Eptam performance (immediate and thorough incorporation gives best weed control). Rates must be adapted for individual conditions. The suggested springapplied Eptam rate is 2 to 3 lb/A. The 3 lb/A rate should give good weed control without crop injury on a soil with a silty clay texture and more than 3% organic matter. The minimum rate of 2 lb/A may injure sugarbeet on a sandy loam or coarsertextured soil with less than 3% organic matter. The Eptam rate should be adjusted within the 2 to 3 lb/A range when the soil is intermediate between the two extremes. Eptam at 2.5 lb/A should give good weed control and little crop injury on clay loams or finertextured soils with more than 5% organic matter.
Some herbicides give good weed control only when organic matter levels are low. Pyramin has not been effective in the Red River Valley, except on the coarsertextured soils with less than 5% organic matter and with above average rainfall. The lower the organic matter, the more effective. Most postemergence herbicides are affected only slightly by organic matter levels. Determine organic matter levels on each field where organic matter sensitive herbicides are to be used. Organic matter levels change very slowly and testing once every 5 years would be adequate.
HERBICIDELIQUID FERTILIZER COMBINATIONS: Thorough mixing and continuous vigorous agitation are required to obtain an even application of herbicideliquid fertilizer combinations. Some herbicideliquid fertilizer combinations will not form a uniform mixture even with thorough agitation. Compatibility of the herbicide in the liquid fertilizer should be tested before the herbicide is added to the tank. The compatibility test may be conducted by combining small quantities of the components being mixed in the same proportions used in the spray tank. Generally, mix 1 pint of fertilizer and 2 teaspoons of the liquid herbicide. For wettable powders, mix 2 teaspoons of powder with a small quantity of water to form a slurry, and add the slurry to the fertilizer. Close the jar and shake well. Watch the mixture for several seconds and check again 30 minutes later. If the mixture does not separate, the combination is compatible. If the mixture separates or gets very thick or syrupy, do not combine for field application. Mixing ability may be improved by adding a compatibility agent such as Compex or Unite. Different batches of fertilizer may differ in their mixing properties so each should be tested separately.
HERBICIDEDRY FERTILIZER COMBINATIONS: Many preplant incorporated herbicides are registered for impregnation on dry bulk fertilizer. Ammonium sulfate, ammonium phosphatesulfate, diammonium phosphate, potassium chloride, superphosphate, treble superphosphate, and urea are some of the approved fertilizer materials for impregnation. Impregnated fertilizer should be applied immediately and incorporated according to label instructions. Accurate spreader calibration and uniform fertilizer distribution are essential. Consult the herbicide label for minimum amounts of fertilizer per acre and for maximum amounts of herbicide per given weight of fertilizer. Ranges of 200 to 400 lb/A of dry bulk fertilizer are recommended to maintain uniformity of herbicide application.
HERBICIDE RESIDUE or the persistence of phytotoxic levels of a herbicide for more than one year can be a problem with some of the herbicides used in North Dakota and Minnesota. Herbicide residues are most likely to occur following years with unusually low rainfall because chemical and microbial activity needed to degrade herbicides is limited in dry soil. Herbicides generally do not disappear from soil due to leaching. Therefore, the rate of herbicide degradation is similar with adequate rainfall or excessive rainfall. Crop damage from herbicide residues can be minimized by application of the lowest herbicide rate which will give good weed control, by using band rather than broadcast applications, and by moldboard plowing before planting the next crop. Moldboard plowing reduces phytotoxicity of some herbicides by diluting the herbicide residue in a large volume of soil and by providing untreated surface soil in which sugarbeet can germinate and begin growth.
Herbicide residues often can be detected by use of a bioassay for herbicide residue. A soil sample representative of the whole field must be obtained by sampling at many places to the depth of the tillage layer. A field which was only tilled shallowly after herbicide application the previous year should be sampled shallowly while a deep tilled field should be sampled as deep as the tillage tool was operated. Also, a sample of soil known to be free of herbicide residue must be obtained from near the treated field to serve as the untreated check. The samples should be dried and the clods broken so that the largest particles are no larger than a wheat kernel. Prepare at least two samples each of the untreated check soil and the test soil. Place the soil in pots or other containers with holes in the bottom for water drainage. The crop to be grown in the field should be used as one bioassay species. Preparing extra pots and testing a more susceptible species may be helpful in detecting residues. Plant in each pot 12 seeds of largeseeded crops like corn or soybeans, or 20 seeds of smallseeded crops like sugarbeet, cereals, or flax. Water the soil as needed for optimum germination and plant growth, but do not overwater. When the plants are about 2 inches tall, thin to about 6 largeseeded or 12 smallseeded uniform seedlings in each container. The containers should be placed in a warm place at about 70 to 75 F and in direct sunlight during the day. Observe the plants in the untreated check and test samples for 2 to 3 weeks after emergence. Some tangible measurements, such as plant height and leaf length, can be taken for evaluation, along with visual observation of abnormalities. Some herbicides, like atrazine and metribuzin, have slow developing symptoms that appear after food reserves in the seed have been depleted so symptoms may not be apparent soon after emergence. The soil should be washed from the roots to observe root growth, especially for dinitroaniline herbicides such as Sonalan, Prowl, and Trifluralin. Window bioassays do not always provide accurate information on Glean, Ally or Classic carryover.
Field Bioassay: Using typical tillage, seeding practices and timings for the particular crop, plant strips of the desired crop variety across the field previously treated with the herbicide. Plant the strips perpendicular to the direction of application. The strips should also be located so that different field conditions are encountered, including differences in soil texture, pH, and drainage. If the crop does not show visible symptoms of injury, stand reduction, or yield reduction, the field can be seeded with the test crop in the growing season following the bioassay. If visible injury, stand reduction, or yield reduction occurs, the test crop should not be seeded, and the bioassay must be repeated the next growing season.
Accent may have a residue the year following application to corn. Field corn can be seeded anytime after Accent application but 10 months should elapse before seeding popcorn or sweet corn. Alfalfa can be seeded 12 months or more after application; dry edible bean and soybean after 10 months; spring wheat, oats and barley after 8 months; and winter wheat and winter rye after 4 months. Sugarbeet and other rotational crops may be seeded 18 months or more after Accent application on soils with pH 6.5 or greater and after 10 months on soils with pH less than 6.5
Ally at 1/267 lb/A (0.1 oz/A of formulated product) may carryover in soil for more than 3 crop years. The most important factor affecting Ally carryover in soil is pH. The rate of Ally breakdown decreases as soil pH increases. Ally should not be applied to soils with a pH above 7.9. The minimum recropping intervals east of Highway 1 in ND are 1 month for spring and winter wheat, and 10 months for durum wheat, barley and oats. Corn, dry bean, flax and sunflower should not be seeded until 34 months have passed and the field had 34 inches of cumulative precipitation. Alfalfa, canola, potato, soybean and sugarbeet should not be planted until after 34 months and 28 inches of precipitation.
Land previously treated with Ally should not be rotated to crops other than those listed above until a field bioassay confirms that residues of Ally are not present.
Amber may have a residue the year following application to wheat or barley. Wheat may be seeded any time after application. Oats and barley may be seeded after 18 months, corn after 22 months and soybean after 36 months. All other crops may be seeded only after the completion of a successful field bioassay. See the Amber label for field bioassay instructions.
Assert may damage crops seeded the year after application. Barley and wheat have no rotational restriction. Corn, drybean, soybean and sunflower can be seeded the next cropping season. Alfalfa, canola, flax, oat and potato can be seeded 15 months after Assert application and sugarbeet can be seeded 20 months after application.
Atrazine (several trade names) generally has a residue the year following application to corn at 2 to 4 qt/A in North Dakota and Minnesota. If soil moisture is deficient, l qt/A of atrazine may cause injury to susceptible crops the following year. Corn and millet are tolerant to atrazine while other crops are susceptible to various degrees. The approximate ranking of other crops from most to least tolerant is flax, soybeans, barley, wheat, oats, sunflower, and sugarbeet.
Banvel4S at 1 to 4 pt/A applied for perennial weed control may persist in the soil and damage crops the next year. Fall applications are more likely to persist than spring applications. Crop injury may occur if the interval between application and planting is less than 45 days per 1 pt/A of Banvel, excluding days when ground is frozen. Research at North Dakota State University indicated that Banvel at 1 pt/A applied the previous fall caused severe sunflower injury and prevented seed production. Sugarbeet is similarly sensitive as sunflower to Banvel.
Basis at 0.015 lb/A (0.33 oz) applied to corn may have a soil residual. Basis is a 2:1 mixture of rimsulfuron and thifensulfuron. The rimsulfuron will carry over while thifensulfuron will not. Sugarbeet may be seeded 10 months after Basis application; soybean after 2 weeks; potato after 4 months; barley, oat and wheat after 8 months; alfalfa after 10 months; sunflower after 12 months; and other crops after 18 months. Risk of carryover of Basis is less than with Accent.
Basis Gold is a mixture of nicosulfuron, rimsulfuron and atrazine and the labelled rate of 14 oz product per acre would be equivalent to 0.01 + 0.01 + 0.76 lb/A of the active ingredients. Basis Gold may have a soil residual. Field corn can be seeded any time after application, cereals and soybean after 10 months, and sugarbeet and all other crops after 18 months. If Basis Gold is applied after July 1, only plant corn or sorghum the following year.
Beacon and Exceed often will have a residue the year following application to corn. In the Red River Valley of Minnesota and North Dakota, corn is the only crop that can be grown for two seasons after the season when the Beacon was applied. In other areas, winter wheat and rye can be seeded 3 months or more after application. Alfalfa, dry bean, soybean, sunflower, and spring seeded small grain can be seeded 8 months or more after application. Other crops can be seeded 18 months or more after application. Beacon applied at Fargo on a pH 8.0 soil in 1989 injured sugarbeet in 1993 but not in 1994.
Broadstrike + Dual (flumetsulam + metolachlor) is labeled for application in corn and soybean and Broadstrike + Treflan (flumetsulam + trifiluralin) is labeled for application in soybean. Dual has few rotation restrictions and all crops can be planted the following year. Consult the Dual label for rotation restrictions within the same year as Dual application.
The Broadstrike component may have a residue the year following application to corn or soybeans. The minimum recropping intervals are 4 months for alfalfa, dry bean, and pea; 4.5 months for barley, oat, rye, and wheat; 18 months for sorghum and sunflower; and 26 months for sugarbeet and mustard crops (rapeseed, canola, mustard, and crambe). Rotation to all other crops requires a 26 month rotation interval and a successful field bioassay.
Broadstrike + Treflan (flumetsulam + trifluralin) is labeled for application in soybean. The amount of trifluralin applied when Broadstrike + Treflan is applied at the labeled rate of 1.5 to 2.25 pt/A is 0.63 to 0.96 lb ai/A, respectively. Therefore, precautions in crop rotation would apply as if trifluralin was applied alone at the respective rates of 0.63 to 0.96 lb ai/A plus the restrictions for Broadstrike should be observed. Consult the Treflan label for additional rotation restrictions for trifluralin.
The Broadstrike component may have a residue the year following application to soybeans. The minimum recropping intervals are 4 months for alfalfa, dry bean, pea, barley, wheat, and rye; 8 months for corn; 18 months for oat, proso millet, annual or perennial grass crops, sorghum and sunflower; and 26 months for sugarbeet and mustard crops (rapeseed, canola, mustard and crambe). Rotation to all other crops requires a 26 month rotation interval and a successful field bioassay.
Classic often will have a residue one or more years following application to soybean. Classic is not labelled in North Dakota. Classic only can be used south of Highway MN 27 and east of Highway US 71 which limits use to a portion of the Southern Minnesota Beet Sugar Cooperative region. A maximum of 1.5 oz/A of product can be used on soils with pH 7.0 or less but only 0.33 oz/A or less on soils with pH greater than 7.0. Following application of Classic in the approved area, cereal grains can be seeded after 3 months and corn, alfalfa, and dry beans after 9 months. Sugarbeet and other crops can not be seeded until a test strip of has been successfully grown to maturity one or more years prior to sugarbeet production.
Peak at 0.75 to 1.0 oz/A may damage crops seeded one or more years after application to wheat, barley, rye or oats. Only corn or small grain should be planted the year after application in the Red River Valley. Outside this area, soybean, dry bean, canola and potato may be planted 10 months after application. The rotation interval for sugarbeet and sunflower is 24 months.
Prowl, Sonalan, and Trifluralin are similar herbicides called dinitroanilines. Under dry soil conditions these herbicides can persist in the soil for more than one year. Sunflower, soybeans, potatoes, and dry edible beans are tolerant to dinitroaniline herbicides. The approximate ranking of other crops from most to least tolerant is flax, barley, wheat, corn, oats, and sugarbeet. Sonalan has less soil residual than Prowl or Trifluralin. Fields treated with Sonalan may be planted to any crop except sugarbeet the next year. Sugarbeet should not be seeded within 13 months of Sonalan except sugarbeet can be seeded after 8 months if 1.1 lb/A or less was applied and the field was moldboard plowed 12 inches deep.
Pursuit at 4 fl oz/A is registered for soybean in Minnesota south of state Highway 210. Rotational restrictions in this area include 4 months after application for wheat, rye, edible bean and peas; 9.5 months for barley and corn; 18 months for popcorn, sweet corn, oats, and sorghum; 40 months for sugarbeet and 26 months for other crops. Pursuit at 3 fl oz/A is registered for soybean north of Highway 210 in Minnesota and in North Dakota. Rotational restrictions in this area include 9.5 months after application for wheat, corn, edible bean, and peas; 18 months for barley, rye and oats; 26 months for sunflower, canola, flax, and potato; 40 months for sugarbeet; and 26 months for other crops. Pursuit carries over more in low pH soils than in high pH soils and sugarbeet injury from Pursuit has been observed 7 years after application on soils with pH less than 6.0.
Reflex at 0.75 to 1 pt/A is registered for postemergence broadleaf weed control in soybean only south of Highway 212 in Minnesota. Sugarbeet should not be planted until 18 months after application of Reflex.
Sencor or Lexone generally is used on soybean in combination with other herbicides or is used on potatoes alone. No harmful residues would be expected when used at 0.33 lb/A product or less. Rates of 0.67 lb/A product or higher could cause damage to susceptible crops the next year. The approximate ranking of crops from most to least tolerant are potato, soybean, dry edible bean, corn, barley, wheat, oats, sunflower, flax, and sugarbeet.
Tordon at 1/64 lb/A active ingredient or 1 oz/A of formulated product may carry over in the soil for more than one crop year. Only grass or grain crops such as small grains, corn, sorghum, or flax should be planted on fields treated with picloram the previous year. Sunflower, soybean, dry edible bean, and potato are especially susceptible to picloram.
Glyphosate (several trade names) is applied postemergence to the weeds but before crop emergence for annual weed control at 0.5 to 2 pt/A. Glyphosate must be used in combination with a nonionic surfactant of at least 50% active ingredient at 0.5% v/v. Addition of ammonium sulfate at 17 lb/100 gallons of water will improve the consistency of weed control with glyphosate, especially when weeds are under environmental stress. Add ammonium sulfate to the water slowly and wait until it is completely dissolved before adding glyphosate or surfactant. Glyphosate at 0.5 pt/A controls foxtails (pigeongrass), 0.75 pt/A controls volunteer small grains, and 1 pt/A controls wild oats and downy brome when applied to plants less than 4 inches tall. The 1 pt/A rate may not control wild buckwheat, Russian thistle, or kochia. Glyphosate should be used at 2 pt/A for control of winter wheat or winter rye seeded as a cover crop. Use the higher rate on larger weeds, more resistant weeds, or if the plants are under moisture stress. When low rates of glyphosate are used, apply in 3 to 10 gallons of water per acre by ground or in 3 to 5 gpa by air. Delay tillage for at least 3 days after treatment. Apply glyphosate at 2 pt/A when quackgrass is at least 8 inches tall (3 to 4 leaf stage) and actively growing. Apply glyphosate at 4 to 6 pt/A when Canada thistle is actively growing and at or before the bud stage. Fall treatment of Canada thistle should be before frost for best results but glyphosate will give good control of quackgrass after frost. Do not till until 3 or more days after treatment. Glyphosate can be used in the spring before or after planting but before emergence of barley, corn, oats, soybeans, dry beans, forages, potatoes, sugarbeet, wheat, and sorghum (milo), or in the fall when these crops will be planted the next growing season.
Gramoxone Extra, a nonselective contact herbicide, can be used at 1.5 to 3 pt/A alone or in combination with a residual herbicide as a substitute for tillage. Gramoxone Extra may be applied before or after planting until just before crop emergence. Apply Gramoxone Extra in 5 to 10 gallons per acre of water by air or in 20 to 60 gallons per acre of water by ground. Add nonionic surfactant to the spray solution at 0.12 to 0.25 % v/v. Gramoxone Extra is corrosive to exposed aluminum spray equipment and aircraft structures so rinse equipment immediately after use. Gramoxone Extra is toxic so avoid contact with the skin; small amounts could be fatal if swallowed. Gramoxone Extra is a restricted use herbicide.
The reasons for using a Pre or PPI herbicide in sugarbeet include the following:
FALL APPLICATION OF HERBICIDES: Certain herbicides may be applied in the fall for weed control the following spring. Included in this group are Eptam, and RoNeet. Fall treatments should be applied after October 15 and until soil freezeup. Application of herbicide treatments after October 15 when soil temperature has cooled minimizes herbicide loss by volatilization. Applications made more than 3 weeks before soil freezeup can result in poor weed control. Both granular or liquid formulations of the herbicides are registered for use in the fall. Fall applications of granular formulations generally have performed more effectively than the liquid formulations, especially under heavy crop residue or cloddy situations.
The use of fall herbicides a) eliminates the need for deep spring tillage thus improving the seedbed, b) may give less sugarbeet injury than spring herbicides and c) allows planting in the spring with no delay for herbicide application. On the negative side, fall herbicides a) may increase soil erosion over winter, b) give more variable broadleaf weed control then when spring applied, c) may require a higher rate and thus cost more than spring herbicides, and d) limit crop choice in the spring.
EPTAM preplant incorporated in the spring at 2 to 3 lb/A or fall applied at 4 to 4.5 lb/A gives good control of annual grasses and certain broadleaf weeds. Eptam sometimes causes sugarbeet stand reduction and temporary stunting. However, no yield reduction will result if enough sugarbeet remain to obtain an adequate plant population after thinning. Eptam should be used with extreme caution on sugarbeet grown in loam or coarser-textured soils with 3% or less organic matter because predicting a safe Eptam rate is difficult on such soils. See previous sections on soil organic matter test, fall application of herbicides and herbicide incorporation for more details.
RO-NEET spring applied at 3 to 4 lb/A or fall applied at 4 lb/A gives weed control similar to Eptam. Eptam tends to give better weed control than Ro-Neet on fine-textured, high organic matter soils or under relatively dry conditions while Ro-Neet gives better control than Eptam when spring rainfall is adequate to excessive. Ro-Neet causes less sugarbeet injury than Eptam and is safer for use on more coarse textured, low organic matter soils. Ro-Neet should be incorporated immediately and thoroughly the same as Eptam.
EPTAM + RO-NEET has less potential for sugarbeet injury than Eptam alone and is less expensive per acre than Ro-Neet alone. The rate of application of the mixture must be adjusted for soil texture and organic matter. Suggested fall applied rates are; Ro-Neet alone at 4 lb/A on soils with less than 3 percent organic matter, Eptam + Ro-Neet at 1 + 3 lb/A on loam or coarser soils with 3 percent organic matter, 1.5 + 2.5 lb/A on loam to clay loam soils with 3 to 4 percent organic matter, 2 + 2 lb/A on clay loam soils with 3.5 to 4.5 percent organic matter, and 2.5 + 2.5 lb/A on clay or clay loam soils with over 4.5 percent organic matter. Suggested spring applied rates are; Ro-Neet alone at 3 lb/A on loam or coarser soils with 3 percent or less organic matter. Eptam + Ro-Neet at 1 + 2.5 lb/A on loam or coarser soils with 3 to 3.5 percent organic matter, 1.5 + 2.5 lb/A on loam to clay loam soils with 3.5 to 4.5 percent organic matter, and 2 + 2 lb/A on clay loam or finer soils with 4 percent or more organic matter. These rates may need to be adjusted on certain fields or with certain incorporation tools based on individual experience. Eptam, Ro-Neet or Eptam + Ro-Neet require immediate incorporation for best weed control.
PYRAMIN spring applied at 3.8 to 7.6 lb/A controls most broadleaf weeds. Pyramin has been more effective on soils with less than 5% organic matter than on heavier soils. Weed control from Pyramin generally increases as soil organic matter content decreases. Shallow incorporation generally improves weed control from Pyramin. Large amounts of rainfall after application improves weed control from Pyramin.
NORTRON SC at 2 to 3.75 lb/A gives good control of several broadleaf and grassy weeds. Nortron is especially effective on redroot pigweed but is weak on yellow foxtail. Nortron generally gives less sugarbeet injury than Eptam especially on more coarse-textured, low organic matter soils. Nortron may be applied preemergence but incorporation generally improved weed control in tests in North Dakota and Minnesota. Operating the tillage tool 1, 2, or 4 inches deep gave similar weed control with slightly better control at 2 and 4 inches compared to 1 inch. Preemergence applications of Nortron will give good weed control when relatively large amounds of rain follow application. The exact amount of rain needed is not known but field observations on fine-textured, high organic matter soils indicate that at least 1 inch of rain is needed to give best results from preemergence Nortron. More coarse-textured, low organic matter soils probably would require less rain for Nortron activation than fine textured, high organic matter soils. Nortron often has a residue the year following use on sugarbeet. Crops most likely to be damaged by Nortron residue are wheat, barley, and oats. Moldboard plowing usually will eliminate crop injury. Nortron should be applied in a band to reduce cost and reduce potential crop injury from residues the following year.
Nortron SC may form an insoluble deposit on the sides of a partially full container. This deposit may plug screens and nozzles. Sprayers should be cleaned immediately after use to avoid drying of spray solution. Partially empty containers of Nortron SC should be filled with water to prevent drying in the container. Mark or record the level of remaining Nortron SC before adding the water.
COMBINATIONS OF SOIL APPLIED HERBICIDES nearly always give improved weed control compared to the use of individual herbicides. Unfortunately the risk of sugarbeet injury also increases with herbicide combinations so selecting the proper rate for each herbicide combination and each farming situation is very important and also sometimes difficult. All agricultural pesticides which are tank mixed should be registered for use as a tank mixture by the Environmental Protection Agency. Agricultural pesticides may be tank mixed if all pesticides in the mixture are registered by the Environmental Protection Agency on the crop being treated. However, users of nonlabeled mixtures must assume liability for any possible crop injury, inadequate weed control, and illegal residues.
Pyramin does not give grass control and Nortron is sometimes weak on grasses; thus these herbicides often should be used in combination with a grass herbicide such as Eptam or RoNeet. Nortron or Pyramin in combination with Eptam or RoNeet sometimes have caused serious sugarbeet injury especially on lighter soils. Nortron + spring applied Eptam has been especially damaging and this treatment only should be used on silty clay soils with over 6% organic matter. Spring applied Nortron or Pyramin over fall applied Eptam has given less sugarbeet injury than combinations applied in the spring.
Relative Control of Weeds with Preemergence or Preplant Incorporated Herbicides
| Incorporation of soil-applied herbicides | Herbicide treatment |
| Deep incorporation required. Tillage tool 4 inches deep. | Eptam, Ro-Neet, Eptam + Nortron. |
| Shallow incorporation required. Tillage tool 2 inches deep. | Ro-Neet + Nortron |
| Shallow incorporation usually improves weed control compared to no incorporation. | Nortron, Pyramin. |
| Relative safety to sugarbeet of soil-applied herbicides | Herbicide treatment |
| Low risk of injury. | Ro-Neet, Nortron, Fall Eptam, Eptam + Ro-Neet, Pyramin. |
| Low to moderate risk of injury. | Eptam, Fall Eptam + Spring Nortron. |
| Moderate risk of injury. | Ro-Neet + Nortron. |
| High organic matter, high clay content soils only. | Spring Eptam + Nortron. |
Postemergence herbicides may need to be used on fields previously treated with a soil applied herbicide for the following reasons:
BETANEX, BETAMIX and BETAMIX PROGRESS are postemergence herbicides for the control of annual broadleaf weeds. Betanex and Betamix occasionally cause sugarbeet injury. Betanex and Betamix should be applied using 0.75 to 7.4 pt/A (0.12 to 1.2 lb/A) and Betamix Progress from 0.5 to 3.3 pt/A (0.12 to 0.75 lb/A). Several factors should be considered when selecting a rate of Betanex, Betamix or Betamix Progress (Progress).
1) Sugarbeet growth stage: Sugarbeet with four true leaves is less susceptible to injury than smaller sugarbeet and sugarbeet gains additional tolerance as plants become larger than the four leaf stage. Betanex, Betamix or Progress at 0.12 to 0.33 lb/A can be applied to sugarbeet with less than four leaves and up to 0.5 lb/A on sugarbeet with four leaves. Applications totalling 0.5 lb/A or less should be followed by a second application in 5 to 7 days if living weeds are present after 5 days and if the sugarbeet plants were not injured significantly. Split application with reduced rates has reduced sugarbeet injury and increased weed control compared to single dose, full rate application. Sugarbeet becomes rather tolerant of Betanex, Betamix and Progress after the plants reach the six- to eightleaf stage. Weeds become more difficult to control as they become larger. Betanex, Betamix or Progress up to 0.75 to 1.2 lb/A can be used on large weeds and six to eightleaf sugarbeet.
2) Environmental Conditions: Betanex, Betamix and Progress give the greatest weed control and sugarbeet injury with high temperatures, high soil moisture, and high relative humidity. Recent flooding or a sudden change from cool and cloudy to hot and sunny weather will increase the risk of sugarbeet injury. Risk of sugarbeet injury is reduced by starting application in late afternoon or later so that temperatures will be dropping rather than increasing after application. The control of weeds can be improved by applying higher rates of Betanex, Betamix or Progress on the morning of a hot day. However, sugarbeet should have six to eight leaves before using this technique. The sugarbeet leaves may be damaged but death of six to eight leaf plants is unlikely and sugarbeet recovers from early season leaf burn without yield loss. The most effective rate of Betanex, Betamix and Progress can change rapidly during a growing season. For example, Betanex at 1.5 pt/A may be best with twoleaf sugarbeet, good moisture, and warm temperatures but Betanex at 3 pt/A may be required for best results a few days later with larger weeds, dryer soil, and cooler conditions. Generally, rates must be adjusted during the spraying season.
3) Use of Soil Applied Herbicides: Sugarbeet and weeds that have been treated with a soil applied herbicide are more susceptible to Betanex, Betamix and Progress than sugarbeet and weeds that have not been treated. Eptam and RoNeet precondition sugarbeet and weeds more than Nortron or Pyramin. Rates of Betanex, Betamix and Progress should be lower when applied to fields previously treated with a soil applied herbicide than when applied to untreated fields.
The following table gives suggested rates for Betanex and Betamix with consideration of sugarbeet size, application method, and the presence of soil applied herbicide. The rates in the table are conservative rates and assume adequate soil moisture, healthy unstressed sugarbeet, and that the weeds emerge about the same time as the sugarbeet. Betanex or Betamix should be applied in late afternoon or evening and another application should be made 5 to 7 days later if needed. Rates in the table may need to be increased for a dry, cool environment or reduced for a hot, wet environment.
| Betanex, Betamix Broadcast Rate | ||||||||
| No soil herbicide | With soil herbicide | |||||||
| Sugarbeet stage | Low press. | High press. or aerial | Low press. | High press. or aerial | ||||
Cotyledon-2 leaf 2 leaf 4 leaf 6-8 leaf |
(lb/A) 0.25 0.33 0.5 0.75 |
(pt/A) 1.5 2.0 3.0 4.6 |
(lb/A) 0.16 0.25 0.4 0.75 |
(pt/A) 1.0 1.5 2.5 4.6 |
(lb/A) 0.16 0.25 0.33 0.5 |
(pt/A) 1.0 1.5 2.0 3.0 |
(lb/A) 0.12 0.16 0.25 0.5 |
(pt/A) 0.75 1.0 1.5 3.0 |
4) Application Method: Research has indicated that Betanex and Betamix applied at 200 psi spray pressure were more phytotoxic to cotyledon to 2 leaf weeds and sugarbeet than Betanex and Betamix applied at 40 psi. Weed control was greater with 15 to 20 gpa at 200 psi than with 8.5 gpa at 200 psi. Betanex and Betamix applied to plants approximately 2 to 3 inches tall gave similar phytotoxicity at 40 to 200 psi. Betanex or Betamix applied to plants approximately 4 to 6 inches tall were more phytotoxic at 40 psi than at 200 psi. Field observations suggest that aerial applications of Betanex or Betamix give results similar to applications at 200 psi. Similar results would be expected from Progress.
TIMELINESS OF APPLICATION is the most important factor in obtaining good weed control with minimal risk of The following table gives suggested rates for Betanex and Betamix with consideration of sugarbeet size, application method, and the presence of soil applied herbicide. The rates in the table are conservative rates and assume adequate soil moisture, healthy unstressed sugarbeet, and that the weeds emerge about the same time as the sugarbeet. Betanex or Betamix should be applied in late afternoon or evening and another application should be made 5 to 7 days later if needed. Rates in the table may need to be increased for a dry, cool environment or reduced for a hot, wet environment. sugarbeet injury from Betanex or Betamix. Sugarbeet in the mid-four-leaf stage (second pair of true leaves half expanded) is significantly more resistant to Betanex and Betamix than smaller sugarbeet. Sugarbeet becomes even more tolerant after the mid-four-leaf stage. However, research and field experience has shown that waiting for most of the sugarbeet plants to reach the mid-four-leaf stage prior to the first application of Betanex or Betamix often results in less than optimum weed control. Weeds become more tolerant to Betanex and Betamix as they become larger and unfavorable weather may prevent the first timely application. Generally, the best combination of weed control, safety to sugarbeet, and low cost is obtained when Betanex or Betamix is first applied at the cotyledon to two-leaf-stage of sugarbeet using reduced rates of 0.12 to 0.25 lb/A. Another treatment of Betanex or Betamix at 0.16 to 0.33 lb/A generally will be needed 5 to 7 days after the first. The need for additional treatments will be affected by continuing germination of weeds and level of control achieved by the first two treatments.
HERBICIDE 273 at 2.0 to 4.0 pt/A gives good control of wild buckwheat and ladysthumb (smartweed). Weed control may be poor when weeds are under even slight drought stress. Sugarbeet should have 4 to 6 leaves before application and should not be treated later than 40 days after emergence. Temperatures should be 60 to 80 F at application. Herbicide 273 in combination with Betanex, Betamix or Betanix Progress should be used at rates of 0.67 to 1.3 pt/A. H-273 applied to fields with water-saturated soil has caused excessive sugarbeet injury. H-273 will give good control even to large wild buckwheat and ladysthumb (smartweed) if the plants are thoroughly covered by spray droplets, temperature is warm, and soil moisture is adequate to surplus.
POAST at 0.5 to 1.5 pt/A plus additives will control annual and perennial grasses. Research at North Dakota State University has indicated that Dash, an oil additive from BASF, and Scoil or SunIt, methylated sunflower oil additives, often give better grass control than other additives when used with Poast. The improved grass control is observed most often with dry soil, large grass, or reduced rates of Poast. Addition of fertilizer to the spray solution often will increase grass control from Poast plus oil additive. The Poast label recommends the addition of fertilizer for increased control of certain grass species. Ammonium sulfate at 2.5 lb/A or 28% ureaammonium nitrate at 0.5 to 1 gal/A is suggested. See the Poast label for rates for various grass weeds. Cultivation between 14 and 21 days after application will improve quackgrass control. Addition of fertilizer to Poast plus oil additive also may improve control of wild proso millet, green foxtail, yellow foxtail, giant foxtail, barnyardgrass, and wooly cupgrass if the water carrier is high in carbonates or bicarbonates.
Poast should be applied with nozzles that deliver 0.1 gal/minute or less at 40 psi (examples, 4001E for banding or 8001XR for broadcasting). Poast band applied through two nozzles per row will give control similar to one nozzle per row if all nozzles are the same size. Poast applied at high spray pressure (over 100 psi) often gives better grass control than applications at 40 psi. However, the risk of damaging spray drift is much greater from high pressure than from low pressure applications.
ULTIMA 160 has the same active ingredient as Poast, sethoxydim. However, Poast has 1.5 lb/gal of sethoxydim while Ultima 160 has 1.3 lb/gal so the amount of Ultima 160 product applied will be greater than the amount of Poast product applied for a particular situation. For example, the labelled rate for Ultima 160 for foxtail species, wildoat and volunteer corn is 20 fl oz/A while the Poast rate would be 16 fl oz/A. See the Ultima 160 label for rates for other grass weeds. The comments regarding Poast would also apply to Ultima 160.
PRISM at 13 to 17 fl oz/A postemergence will control annual grasses while 17 to 34 fl oz/A is needed for quackgrass control. Retreatment of quackgrass regrowth also may be needed. Prism should be used with an oil additive at 1% v/v for best grass control. Prism should be applied in 5 to 40 gallons per acre of spray solution at 30 to 60 psi by ground and in 3 to 10 gallons per acre by air. Drought and/or cold may reduce grass control. Use of Betanex, Betamix, Betamix Progress or H-273 as a tank-mix or within one day prior to Prism may reduce grass control. However, research in eastern North Dakota indicated that grass control from Prism was reduced less than grass control from Poast by tank-mixing Betanex or Betamix with the grass herbicides. Select has the same active ingredient as Prism but Select has 2 lb/gal ai rather than 0.94 lb/gal ai as in Prism. Select was registered for use on sugarbeet in 1997 and weed control from Select should be identical to Prism when equal amounts of active ingredient are compared.
ASSURE II at 7 to 10 fl oz/A plus an oil adjuvant will control annual grasses while 10 to 12 fl oz/A is needed for quackgrass. Assure II is especially effective on quackgrass compared to other similar herbicides although retreatment may be necessary. Assure II is less effective on yellow foxtail than on other annual grasses so a minimum of 8 fl oz/A should be used on yellow foxtail. See the label for weed sizes and rates for specific grasses. Suggested spray volumes on the label are from 10 to 40 gpa at 25 to 60 psi by ground and 3 to 5 gpa by air. The maximum use rate per season is 25 fl oz/A. Various stresses to grass weeds may reduce grass control from Assure II.
STINGER at 0.25 to 0.67 pt/A postemergence controls several broadleaf weeds and volunteer crops. Stinger at 0.25 to 0.5 pt/A is most effective when applied to common cocklebur, giant ragweed, volunteer sunflower, wild sunflower, marshelder, volunteer alfalfa and volunteer soybeans up to the sixleaf stage, and common ragweed up to the fiveleaf stage. Stinger at 0.5 pt/A is most effective on wild buckwheat in the three to fiveleaf stage before vining begins. Stinger at 0.5 to 0.66 pt/A is most effective on Canada thistle in the rosette to prebud growth stage, but rosette application often gives better control than later application. Stinger must be applied to sugarbeet in the two to eightleaf stage and at least 105 days prior to harvest. Stinger is not registered for application by aircraft. Wheat, barley, oats, grasses, field corn, or sugarbeet can be planted anytime after Stinger application. Do not plant alfalfa, canola, popcorn, sweet corn, or safflower for 10.5 months after application. Do not plant dry bean, soybean, or sunflower for 10.5 months after application, or 18 months after application if soils contain less than 2% organic matter and natural precipitation is less than 15 inches during the 12 months after treatment. Do not plant other crops including pea, lentil, potato, and broadleaf crops grown for seed for 18 months after application. A field bioassay is suggested before seeding sensitive crops on soils with 2% or less organic matter and less than 15 inches annual precipitation. Stinger is a slow acting herbicide. The full effects of the herbicide may not be evident until 30 or more days after application.
UPBEET is a postemergence herbicide that should be used in combination with other broadleaf herbicides such as Betanex, Betamix, Betamix Progress or Stinger. UpBeet provides improved control of several broadleaf weeds such as kochia, redroot pigweed, prostrate pigweed, common mallow, Venice mallow, velvetleaf, nightshade, nightflowering catchfly, ladysthumb (smartweed), wild mustard and sunflower. UpBeet plus Stinger should be applied with an adjuvant but UpBeet in combination with Betanex, Betamix or Betamix Progress does not require an adjuvant. UpBeet will antagonize grass control from Poast, Ultima 160, Prism, Select or Assure II similar to the antagonism caused by Betanex, Betamix or Betamix Progress. The lowest labelled rate of UpBeet is 0.5 oz 50 DF/A. Research in eastern North Dakota and Minnesota has shown that Betanex + UpBeet applied once at 1.5 pt + 0.5 oz 50 DF/A followed 7 days later by 2.0 pt + 0.5 oz 50 DF/A generally gave less weed control than Betanex + UpBeet applied three times at 7 day intervals using 1.0 pt + 0.25 to 0.3 oz 50 DF/A in each treatment. Betanex or Betamix plus Stinger plus UpBeet has provided excellent control of most problem weeds in research conducted in eastern North Dakota and Minnesota. UpBeet use in a single growing season should not exceed 1.5 oz 50 DF/A.
COMBINATIONS OF POSTEMERGENCE HERBICIDES give more broad spectrum and greater total weed control compared to individual herbicides. The risk of sugarbeet injury also increases with combinations so combinations should be used with caution.
All agricultural pesticides which are tank mixed should be registered for use as a mixture by the Environmental Protection Agency. Pesticides may be tank mixed if all pesticides in the mixture are registered by the EPA on the crop being treated. However, users of nonlabeled mixtures must assume liability for any possible crop injury, inadequate weed control, and illegal residues.
A tank-mixture of one of the grass control herbicides (Poast, Ultima 160, Prism, Select, Assure II) plus an adjuvant plus one of the broadleaf control herbicides (Betanex, Betamix, Betamix Progress or H-273) will often give less grass control than the grass herbicide plus adjuvant. The broadleaf herbicide antagonizes the grass control from the grass herbicide but broadleaf control is not reduced by the presence of a grass herbicide. Stinger does not antagonize grass control.
Relative Control of Weeds with Postemergence Herbicides
Antagonism of grass control by a broadleaf herbicide may not be significant if the environment and the condition of the grass favors excellent weed control. Antagonism is less likely to be a problem with small grass, optimum soil moisture, and a grass that is actively growing. A grass species that is very susceptible to the grass herbicide chosen will be antagonized less than a more tolerant grass species. For example, antagonism of Ultima 160 would be greater on wild oat and volunteer grain than on green or yellow foxtail while antagonism of Assure II would be greater on yellow foxtail than on wild oat and volunteer grain.
Antagonism will be less if an adjuvant is included in the mixture of grass herbicide plus broadleaf herbicide as compared to not using an adjuvant. However, excessive sugarbeet injury may occur from a broadleaf herbicide plus an adjuvant.
Antagonism can be nearly eliminated by applying the grass herbicide plus adjuvant 24 hours before the broadleaf herbicide or by applying the broadleaf herbicide 3 to 5 days before the grass herbicide. Also, research results indicated that a full rate of grass herbicide plus a broadleaf herbicide (no adjuvant) applied twice at a 7-day interval gave grass control nearly equal to a single application of the grass herbicide plus adjuvant.
Stinger plus H-273 gave better control of wild buckwheat than Stinger, H-273, Betanex, Betamix, or Stinger plus Betamix in field experiments in North Dakota and Minnesota. Stinger plus Betamix or Betanex split applied gave better control of common lambsquarters, Russian thistle, wild buckwheat, ladysthumb (smartweed), eastern black nightshade, common cocklebur, lanceleaf sage and buffalo bur than Betamix or Betanex alone or Stinger alone. Stinger alone controlled common sunflower, Canada thistle, and giant ragweed as well as Stinger plus Betamix or Betanex. Sugarbeet injury from Stinger plus Betanex or Betamix generally is similar to the total of % injury from Stinger alone plus Betanex/Betamix alone. Sugarbeet injury from Stinger at 0.5 pt/A averaged over 25 experiments in 1989 and 1990 was 3%. The highest observed injury was 8%. Therefore the risk of additional sugarbeet injury is low from adding Stinger to Betanex or Betamix.
UpBeet plus Betanex, Betamix or Betamix Progress has provided improved control of redroot pigweed, prostrate pigweed, kochia, common mallow, nightshade, ladysthumb (smartweed), Venice mallow, nightflowering catchfly, wild mustard and velvetleaf compared to Betanex, Betamix or Betamix Progress alone. UpBeet generally has little effect on sugarbeet injury. A three-way combination of Betanex + UpBeet + Stinger has given good to excellent control of all common broadleaf weeds in sugarbeet in research conducted in North Dakota and Minnesota.
H-273 has been used in combination with Betanex or Betamix to give improved control of wild buckwheat and smartweed spp. compared to Betanex or Betamix alone. H-273 should be used at 0.67 pt/A in combination with Betanex or Betamix when sugarbeet has less than four leaves. H-273 can be used at up to 1.3 pt/A in combination when sugarbeet has four or more leaves. Betanex or Betamix plus H-273 at 0.67 pt/A gives similar sugarbeet injury but sometimes gives less control of redroot pigweed and common lambsquarters as compared to Betanex or Betamix alone.
Nortron SC (ethofumesate) is registered as a tank-mix combination with Betanex (desmedipham). Nortron SC plus Betanex gives increased weed control and greater risk of sugarbeet injury than Betanex alone. The active ingredients should be used in a 1 part ethofumesate: 2 parts desmedipham ratio. Factors affecting risk are the same as for Betanex alone.
Betamix Progress (desmedipham + phenmedipham + ethofumesate) applied POST gives increased weed control and greater risk of sugarbeet injury than Betamix alone. The active ingredients are premixed in a 1:1:1 ratio. A tank mixture of Betamix plus Nortron SC can substitute for Betamix Progress but the ratio of the three active ingredients should be maintained as 1:1:1.
Determining the Application Rate of Betanex + Nortron SC, Betamix + Nortron SC, or Betamix Progress.
The total pounds per acre of active ingredient in Betanex + Nortron SC, Betamix + Nortron SC, or Betamix Progress should be equal to the normal total pounds per acre of active ingredient of Betanex or Betamix that would be applied alone for a given situation. The ratio of active ingredients should be maintained at one part Nortron to two parts of Betanex or Betamix. This is the premix ratio in Betamix Progress. Therefore, the normal rate of Betanex or Betamix should be reduced by one-third and the Nortron SC added to replace the Betanex or Betamix.
The following procedure can be used to determine the appropriate rate of the combinations.
1. Determine the appropriate or normal rate of Betanex or Betamix that would be used alone for a given situation.
2. Reduce the normal rate of Betanex or Betamix by one-third.
3. Multiply the normal rate of Betanex or Betamix in pt/A by 0.11 to determine the pints of Nortron SC to add to the reduced rate of Betanex or Betamix so that the total pounds per acre of the combination is equal to the normal pounds per acre of Betanex or Betamix alone.
Example:
The following procedure can be used to determine the appropriate rate of the premix, Betamix Progress.
1. Determine the appropriate or normal rate of Betamix that would be sued alone for a given situation.
2. Multiply the normal rate of Betamix in pt/A by 0.75 to determine the rate of Betamix Progress in pt/A so that the total pounds per acre of Betamix Progress is approximately equal to the normal pounds per acre of Betamix.
Example:
Sugarbeet becomes more tolerant to herbicides as sugarbeet size increases. Herbicides and herbicide combinations vary in potential for herbicide injury. The following groups of herbicide treatments listed by a sugarbeet leaf stage indicate that the treatments usually can be applied safely to sugarbeet in the given leaf stage or to larger sugarbeet. Leaf stage refers to the number of true leaves and does not consider cotyledonary leaves. Herbicide rates are broadcast active ingredient. Treatments should be repeated in 5 to 7 days if necessary for adequate weed control.
RELATIVELY SAFE POSTEMERGENCE TREATMENTS AT FOUR GROWTH STAGES OF SUGARBEET, BROADCAST RATES.
Sugarbeet in the cotyledon to early twotrueleaf stage.
Sugarbeet in the twotrueleaf stage.
Sugarbeet in the midfourleaf stage.
Sugarbeet in the six leaf stage.
Application of the listed treatments at the proper leaf stage of sugarbeet does not guarantee that sugarbeet will not be injured because environmental conditions can affect postemergence herbicide performance.
High temperatures with good soil moisture and especially a sudden change from cool, cloudy, and wet conditions to hot and sunny can increase the phytotoxicity of postemergence sugarbeet herbicides. When existing or predicted weather conditions would be expected to cause increased sugarbeet injury, then a herbicide treatment with less risk of sugarbeet injury should be used. For example, a rate of 1.5 to 2.0 pt/A of Betanex should be substituted for 3.0 pt/A of Betanex on 4-leaf sugarbeet when the environment would be expected to cause increased sugarbeet injury.
LAYBY HERBICIDES
TRIFLURALIN (several trade names) at 0.75 lb/A is cleared for use on sugarbeet when the sugarbeet is 2 to 6 inches tall and well rooted. Exposed beet roots should be covered with soil before application. Emerged weeds are not controlled. Trifluralin may be applied over the tops of the sugarbeet and incorporated with a harrow, rotary hoe, or cultivator adjusted to mix the herbicide in the soil without excessive sugarbeet stand reduction. Use of trifluralin can reduce the emergence of late season weeds which often cause problems in sugarbeet. Occasional girdling of sugarbeet plants from trifluralin has been observed. This girdling usually does not cause significant yield loss. Soil residue harmful to wheat or barley is not likely the year after application. However, barley is more tolerant of trifluralin than wheat and should be grown following layby trifluralin and a dry year.
EPTAM at 3 lb/A is cleared as a layby herbicide for sugarbeet and should be applied similarly to trifluralin. However, the greater volatility of Eptam and the greater need for thorough incorporation make Eptam less likely to be effective as a layby herbicide than trifluralin. Eptam also can be applied by metering the herbicide into irrigation water. Eptam should be applied in the first irrigation after the last cultivation of the sea.
HAND WEEDING
Proper use of herbicides can provide very good control of most common weeds in sugarbeet. However, herbicides rarely give 100% weed control even under optimum conditions and herbicides occasionally will provide only fair to poor weed control for a variety of reasons. Unfavorable environment, improper timing of application, rates too low for the situation, very high weed populations, and late season weed emergence are some of the most common reasons for disappointing weed control.
Hand weeding is an effective and widely used supplement to herbicides and cultivation for weed control in sugarbeet. Some advantages of hand weeding are:
1. Hand weeding will reduce losses due to weed competition. Losses due to weed competition are proportional to weed density. At some low weed density, the value of the increase in yield from weed control will be equal to the cost of the weed control. This economic threshold is very difficult to predict because many factors impact yield loss due to weed competition. Weed density, weed species biology, date of crop and weed emergence, rainfall, soil temperature, row width, date of weed removal, previous herbicide use and the planned method of weed control, all can affect the economic threshold of weeds in sugarbeet. However, competition experiments in sugarbeet suggest that one or fewer weeds per 100 feet of sugarbeet row will be lower than the economic threshold regardless of other factors. The economic threshold weed density often will be greater than one weed per 100 feet of row but a lower economic threshold is unlikely.
2. Hand weeding will prevent weed seed production and reduce weed densities in the future. Hand weeding densities of weeds that are below the economic threshold may be beneficial if the field has a relatively low level of weed seed in the soil. However, a few more weed seed produced in a field already loaded with seed would be of little consequence.
3. Hand weeding can prevent seed production by weeds that are resistant to the herbicides that were applied and slow the buildup of herbicide resistant weeds.
4. A weed-free field is more attractive than a weedy field.
Evaluation of Weeding and Thinning by Hand Labor in Sugarbeet
Each year a few disputes arise between sugarbeet growers and hand labor who weed and thin sugarbeet. Generally the disputes involve the relative quality of the work performed and the fair price for the work performed. The evaluation of quality and relative value of hand labor performed can be quite complicated.
A definition of an ideal result from hand weeding and hand thinning may be useful as a target. The ideal result will be defined here as 35,600 uniformly spaced sugarbeet plants per acre (150 plants per 100 feet of 22-inch rows) with zero weeds left alive. The ideal result will rarely be achieved for a variety of reasons, some of which follow.
Reasons why weed free fields with 35,600 plants per acre may not be achievable:
The ideal result from hand weeding and hand thinning will only be achieved rarely. However, a very good level of hand weeding and hand thinning can be achieved. Some considerations in evaluating the quality of the hand weeding and hand thinning follow.
in a weedy field. Sugarbeet plants growing within 0.5 inch around each sugarbeet plant would be unhoeable without removing the sugarbeet plant.
| 1200 inches in 100 ft beet plants/100 ft |
= | inches between beets. |
| 1.0 inch unhoeable per beet plant inches per beet plant |
= | portion of row that cannot be hoed without removing the sugarbeet plant. |
Portion unhoeable X weeds per 100 ft = beets per 100 ft removed by hoeing.
The following table was developed using the formulas above.
Table 6. Mathematical estimate of surviving sugarbeet plants after hoeing with various levels of weeds assuming all weeds were hoed out and a starting sugarbeet population of 150 plants per 100 ft of row.
| Starting weeds per 100 ft row |
Starting beets per 100 ft row |
Ending beets per 10 ft row |
| 25 50 100 200 400 800 |
150 150 150 150 150 150 |
147 144 138 125 100 50 |
The numbers in Table 6 indicate that a population of 200 weeds per 100 feet of row or less can be hand weeded in a starting beet population of 150 plants per 100 feet of row with a very adequate remaining sugarbeet population of 125 plants per 100 feet of row or more left after weeding. Hoeing of weed populations of more than 200 weeds per 100 feet of row would result in less than desirable sugarbeet populations.
Table 6 indicates that hand labor cannot be expected to remove dense weed populations with a detrimental effect on sugarbeet populations. Herbicides should be used to lower the weed populations so that ahnd weeding can be done and an adequate population can be maintained. Increasing density of seeding in a weedy field would increase the probability of retaining an adequate population of sugarbeet.
An estimate of the hours required to hand weed a field can be determined by counting weed population and using the following formula developed by Dr. Steve Miller at the University of Wyoming using student labor. Skilled labor may work faster than indicated in the formula.
| Time for hand | 2 hrs per acre | 0.5 hr per |
| weeding in | for walking and | + 1000 weeds |
| hours per acre | looking | for weeding |
As expected, higher weed populations will take longer for weeding and the cost per acre would be higher. In 22-inch rows, one weed per 25 feet of row could be removed in 2.5 hours per acre while one weed per foot of row would take 14 hours per acre according to the formula.
Disputes between sugarbeet growers and hand labor who do thinning and weeding can be reduced by the following actions.
CONTROL OF LIVING COVER CROP
Production of sugarbeet in association with a living cover crop will reduce soil erosion and will protect small sugarbeet plants from damage caused by wind. Living cover crop can be fall seeded or spring seeded. Winter rye is more winter hardy than winter wheat so winter rye is the better choice for a fall seeded cover crop that will still be alive in the spring in eastern North Dakota and Minnesota. A spring seeded cover crop in eastern North Dakota and Minnesota normally would be seeded a few days to a few hours before the sugarbeet. Barley and oats are good choices for a spring seeded cover crop since seed is relatively inexpensive and early spring growth is vigorous. The research conducted was with barley.
Living cover crops are potentially beneficial. However, a cover crop will compete with sugarbeet just like a weed. Timely control and proper seeding rate are important to minimize sugarbeet yield loss from competition. Fall seeded winter rye is much more competitive than spring seeded barley but the rye also provides more protection from wind damage and soil erosion.
Research in eastern North Dakota and Minnesota has shown that winter rye as a cover crop fall seeded at 22 lb/A caused more sugarbeet yield loss than winter rye seeded at 15 or 7.5 lb/A. Barley as a cover crop spring seeded at 48 lb/A caused more sugarbeet yield loss than barley seeded at 24 or 12 lb/A. Sugarbeet yield loss from the highest tested seeding rates probably was from increased competitive ability of higher populations of rye and barley and from the lower level of control by herbicides in the plots with higher populations of cover crop. Therefore, seeding rates of about 15 lb/A of winter rye or 24 lb/A of barley are suggested as a compromise between reducing competition and optimizing protection from the cover crop.
Living cover crop must be controlled on time to avoid sugarbeet yield loss from competition. Winter rye growing near the sugarbeet row must be controled at or before sugarbeet seeding. A band application of Roundup would be an effective method of control. A one-weed delay in controlling winter rye after seeding sugarbeet caused a loss in sugarbeet yield in research. Living rye between the sugarbeet rows should be controlled by the time that the sugarbeet reaches the two leaf stage. Sugarbeet still needs protection from wind at this small growth stage so the rye could be treated with one of the postemergence grass herbicides and then left uncultivated until the sugarbeet plants are large enough to be safe from wind damage. The field could be cultivated after the sugarbeet plants were safe from wind to remove rye plants not fully controled by the herbicide and emerged weeds.
Spring seeded barley growing near the sugarbeet row should be controlled by the time the barley has three leaves. Barley between the rows can be left longer for additional protection from wind. Barley between the rows should be controlled by the time the sugarbeet has four leaves and the barley has 4 to 5 leaves. Barley between the rows could be controlled by cultivation or by a postemergence grass herbicide. The postemergence grass herbicide option would allow an extended period of protection since the dead and dying cover crop will provide some protection from wind.
Sugarbeet Table
Glossary of Chemical Names
1996 Sugarbeet Research and Extension Reports. Volume 27, pages 3-30.
