Albin W. Anderson, Assistant Professor
Department of Entomology
North Dakota State University
Early sugarbeet seeding was again possible during 1977. All white grub and sugarbeet root maggot plots were established and treated by May 2, 1977. The fields at Galchutt and St. Thomas were dry at planting and rains in early May were welcome but resulted in some crusting problems and spotty stands. Replanting was necessary in some of the experiments at St. Thomas.
Sugarbeet Root Maggot: Sugarbeet root maggot adults were first noted in fields near Galchutt on May 11 and at St. Thomas on May 13, 1977. This emergence was nearly three weeks earlier than the average emergence date in the valley which is the end of May. Peak emergence occurred around May 23, again nearly three or four weeks earlier than the long time average. Fly activity continued through mid June at St. Thomas.
The very dry season during 1976 was notable for the low number of sugarbeet root maggot adults and little damage to sugarbeets from this insect throughout the valley. During the 1977 season, however, maggot populations were back to near normal levels in all areas of the valley and heavy damage occurred in untreated beets. It is apparent that a single dry season is not sufficient to significantly reduce population levels of the sugarbeet root maggot.
Laboratory research has shown that there are several stages in the life cycle of the sugarbeet root maggot that are are susceptible to very dry conditions. Pupal formation and adult emergence are adversely effected by dry conditions with high mortality noted. Egg desiccation with high mortality also occurs with low moisture levels and further mortality to the 1st stage maggots is apparent under these conditions.
The high reproductive potential of the sugarbeet root maggot provides a mechanism which enables this insect to withstand adverse physical or chemical factors. Our laboratory data suggest that 96Z mortality due to natural and chemical factors can occur within a population during the growing season and not significantly decrease the potential population at the beginning of the next growing season. We have also shown that when field collected maggots are brought into the lab and subjected to a cold period prior to normal pupation and emergence temperatures, a percentage of the population does not pupate and continue development. These insects represent about 6t of a given population and apparently a second period of cold is necessary for continued development. Within any field population of sugarbeet root maggots then, a percentage will remain in the soil and additional year and pupate and emerge during the second year.
Several fields planted to sugarbeets in 1975 were monitored during the spring of 1977. Maggots, pupae, and adults were found in these fields. The data suggest that there was a greater percentage of root maggots emerging from these 2 year beet fields than during normal years. Further work will continue but there are indications that under very dry conditions, a larger percentage of the population remain deep in the soil and additional year to pupate and emerge the second spring.
White Grubs: White grubs have caused significant economic damage in sugarbeets for several years near Galchutt, North Dakota. During the 1977 season, some grub damage was recorded near Breckenridge and also near Ada, Minnesota.
Extensive efficacy trials were established near Galchutt, North Dakota. During seeding, large numbers of adult beetles were present just below the surface in three fields in which plots were established. During the following two week period, tremendous numbers of adults emerged. White grubs have a three year life cycle with adults emerging every third year. The adults emerge, generally move to trees to feed and mate. Eggs are normally laid in grassy sod. In all fields, however, eggs were laid in the beet field within the beet rows. These young grubs will feed during the summer and move deep in the soil until the following spring when they again move toward the surface and feed through the second summer. Grubs will overwinter and appear again in the spring to feed briefly through late May or June. White grubs then pupate and adults emerge within two or three weeks to repeat the cycle.
Damage in sugarbeets during the first year of the cycle is minimal because by the time the eggs hatch, the sugarbeets are larger and able to withstand some feeding. This was evident during 1977 with little stand loss noted in fields. Because of this, the field trials could not be evaluated and no test results were possible. The greatest damage generally occurs during the second year of the cycle which will be in 1978. We hope to established extensive plot trials in these fields next season to determine effective chemical controls.
Cutworms: It is nearly impossible to accurately predict cutworm activity in a given field and this hinders our efforts to establish effective trials at planting time. One major cutworm control experiment was established near Auburn, North Dakota, testing both registered and experimental insecticides. No cutworm activity was noted in this field and the experiment was lost. Moderate to heavy cutworm damage did occur around May 23 near Barnesville, Minnesota, and at Dwight, North Dakota. Field trials were established near Dwight where the heaviest infestations occurred. A second trial was established at St. Thomas using laboratory reared cutworms in small (microplots) plot trials.
Field investigations during 1977 involved efficacy trials with registered materials, screening candidate insecticides, evaluation of pre vs. post beet emergence applications, and evaluation of-in-furrow applications of granular materials.
Insecticide performance was evaluated on the basis of damage ratings and yield estimates at harvest. Damage ratings were taken on 8 beets per plot on July 11, 1977, and recorded on the basis of the following scale
Yield estimates are based on two 36 foot sections from each plot for a total sample from 72 feet of row.
The plot site at St. Thomas was dry during planting with a 2-3 inch layer of powder dry soil at the surface. A hard driving rain on May 5, 1977 resulted in crust formation and the stand in some experiments was thin and spotty. The stand in the in-furrow test and pre vs. post emergence test was judged sufficient to obtain damage ratings but not yields at harvest. No reseeding was done and these experiments were evaluated on the basis of damage ratings only.
Reseeding was necessary in the registered test and the experimental test plots. We did not have a weed problem and the plots were first cultivated and then reseeded directly into the row over the cultivator band. This was done on May 25, 1977. The second seeding produced a good uniform stand.
The maggot fly population was heavy at the time these plots were reseeded but declined rapidly over the next ten days. Sugarbeet root maggot feeding pressure and damage was not as heavy as would normally be expected in these reseeded plots. Efficacy trials rely on heavy maggot pressure and the results presented may not accurately reflect maggot control due to chemical activity.
Evaluation of Registered Insecticides: This test was conducted on the Green Tucker farm near ST. Thomas, North Dakota. Beets were seeded with a 6-row planter equipped with Noble applicators and included ten treatments replicated four times in two row plots 60 feet long. Granular insecticides were applied in a 5-7 inch band at planting and lightly incorporated in the soil with drag chains. Damage ratings were taken on July 11 and the plots harvested September 20, 1977. The results are shown in Table 1.
The low damage ratings indicate the light maggot pressure in the reseeded test. The 4 ton difference in yield between the check and the highest yield further substantiates this. Light maggot pressure makes it difficult to evaluate differences in efficacy among insecticides.
Experimental Insecticides: In this experiment, 14 treatments were replicated four times in plots consisting of 60 foot rows. Each two row plot was separated by two untreated rows. Beets were planted with a 6-row planter equipped with Noble applicators. Granular materials were applied in a 5-7 inch band and lightly incorporated with drag chains. The results are shown in Table 2.
The low damage ratings again indicate light maggot pressure. Dacamox and Lorsban have performed well in previous tests and show promise for future commerical use. Further testing with these materials will be conducted.
Pre vs. Post Beet Emergence Test: In this experiment, 9 treatments were replicated four times in plots consisting of 100 foot rows. Each two row plot was separated by two untreated rows. Granular materials were applied in a 5-7 inch band and lightly incorporated with drag chain. The post emergence treatment was applied in a 5 inch band and lightly incorporated with drag chains. The stand in this test was judged adequate for damage ratings and nn rmnl~ntinp =~ necessary. The results are shown in Table 3.
Temik performed well when applied both at planting and post emergence. Counter, Dyfonate, and Diazinon all performed better when applied at planting. The damage ratings indicate moderate maggot pressure in the test.
In-Furrow Test: In this experiment, 14 treatments were replicated four times in plots consisting of 100 foot rows. Each two row plot was separated by two untreated rows. Band applications were in a 5-7 inch band and lightly incorporated with drag chains. In-furrow applications were applied 'down the tube' behind the discs placing the granules slightly above the seed but not indirect contact with the seed. The beets were seeded May 1 and damage ratings taken on July 11, 1977. The results are shown in Table 4.
The results, while inconclusive, suggest that certain materials can be applied in-furrow at lower rates and provide good control. Previous tests substantiate this. Further work of this type is indicated.
Sugarbeet Root Maggot Control - 1978: The insecticides registered for sugarbeet root maggot control are shown in Table 5. Early beet seeding in 1976 and 1977 resulted in better growth and larger beets at the time of sugarbeet root maggot emergence. Stand loss due to maggot feeding was not a significant problem simply because larger beets can withstand greater maggot pressure. Insecticide applications are essential in all areas of the valley where this insect occurs, however, since feeding does reduce yields at harvest significantly.
The moisture situation in the valley greatly improved during the summer and fall of 1977. Heavy snow this winter would indicate that early beet seeding may not be possible in 1978. Late spring seeding normally results in young beet plants in the fields at the time root maggot adults are laying eggs and maggots are beginning to feed. Significant losses do occur when maggots attack the younger, more susceptible beet plants are careful consideration must be given to chemical control measures.
Planting time applications are recommended in all areas with a previous history of maggot problems. Temik has performed extremely well over the years and provides excellent control. Counter has consistently provided good control in field trials with yields comparable to Temik treated beets but generally slightly lower. Dyfonate and Diazinon also provide good control of the sugarbeet root maggot. Furadan provides good control but label restrictions must be followed regarding crops which can and cannot follow in rotation.
An extremely heavy cutworm infestation occurred near Dwight, North Dakota both in sugarbeets and sunflowers. Cutworms completely destroyed several acres of both crops requiring a second and third planting in some areas. Cutworms were so numerous that 600-1000 could be hand collected in an hour or two. The insects left several acres completely bare except for large thistle plants. At this time, large numbers could be found congregating beneath the thistle and in most cases, actively feeding on this weed. Several species were involved but most common were the dark-sided and red backed cutworm.
Large numbers of both species were collected and returned to the laboratory. Artificial diets have been developed for these insects and it was our intention to establish a laboratory colony of both cutworm species. This will enable us to study the insects under controlled conditions but more importantly, laboratory reared cutworms can be used to artificially infest beets both in the lab and field to evaluate presently used and experimental materials. This is of particular value in that it will permit testing on a yearly basis with known populations under somewhat controlled conditions.
An experimental weed control trial was established in the Dwight field and when damage was noted this plot was treated with Sevin 5Z bait at 30 pounds per acre. This single treatment was extremely effective and later evaluation indicated 967 control. Where moisture was available, Sevin bait produced good results in other areas of the valley.
A replicated experiment was established on replanted beets in this field using presently registered granular insecticides for maggot control and experimental compounds. The beets were replanted by the grower. Nine treatments were replicated four times in plots consisting of 100 foot rows. Each two row plot was separated by two untreated rows. Granular materials were applied in a 3-5 inch band and lightly incorporated with drag chains. Liquid materials were applied in a band over the row after beet emergence (2-4 leaf stage) when cutworms were first noted feeding in these replanted beets. Of the granular materials applied that are presently registered for root maggot control, Temik was inadvertently omitted. This material should have been included for testing and will be in future trials. The results of this test are shown in Table 6.
Stand counts were taken when cutworm activity began. Heavy populations of cutworms were noted at this time throughout the field. Five days after the stand counts were started extremely high winds were recorded in this area. This produced girdling in the young plants and in some areas, the blowing sand combined with the winds to cut off the plants at ground level. Stand counts were continued for a period after the wind damage but it became very difficult to differentiate between cutworm damage and wind damage. For that reason, the data presented reflect stand reductions recorded during the initial five days of the test.
Of the materials tested, SD43775, Counter, Lorsban, and Diazinon showed promise for future testing. SD43775 is a synthetic pyrethrum (Shell Chemical Company) which appeared to provide excellent control in the test. Only one application was made since the test was shortened. In addition to the low mean stand reduction, large numbers of dead cutworms were found at the surface within the plots treated with this material. This was also noted in preliminary test conducted earlier in another field. Laboratory tests will be conducted with this material as well as future field trials. The other granular materials show some promise but there was only a period of 12-14 days between planting and treating and the stand count evaluation. Under normal commerical conditions, a greater period of time would be expected between application and cutworm activity and this might reduce the effectiveness of these treatments. Counter and Diazinon are presently used for root maggot control and Lorsban is still in the preregistration stage of development. Further work of this type is planned.
Cutworm Microplots: A microplot trial was established using field collected cutworms to artificially infest plots. An existing stand of beets was blocked out into individual plots 6 feet by 4 feet with four replications. Each plot was surrounded by corrugated sheeting pushed at least 4 inches into the soil and extending at least 4 inches above the ground to insure that the cutworms could not escape. The stand in each plot was counted prior to introducing the cutworms. Fifteen cutworms were introduced into each plot during the evening hours and lightly covered with soil. Application of the liquid materials was made with a hand sprayer on the following afternoon. Stand counts were taken at intervals thereafter. The results of the test are shown in Table 7.
The total stand reduction figures are lower than expected because the beets were larger than might be ideal for this type of test and able to withstand some feeding, Sevin WP is registered for cutworm control and is an effective material. SD43775, Sumithion, and Lorsban liquid are all experimental materials but show promise for future testing.
1977 Sugarbeet Research and Extension Reports. Volume 8, pages 128 - 136.
