IN-FURROW AND POSTEMERGENCE APPLICATION OF QUADRIS FOR CONTROL OF
RHIZOCTONIA DAMPING-OFF AND ROOT AND CROWN ROT
Jason R. Brantner and Carol E. Windels
Research Fellow and Professor of Plant Pathology
University of Minnesota, Northwest Experiment Station, Crookston
Rhizoctonia solani (=R. solani) causes seed rot, damping-off (rotting near the soil surface and death of seedlings) during the early part of the growing season and also causes root and crown rot of adult sugarbeet plants. Two strains of R. solani (AG-2-2 and AG-4) are involved. Rhizoctonia solani AG-4 frequently causes seed rot and damping-off, but is not pathogenic to older roots. Rhizoctonia solani AG-2-2 primarily causes root and crown rot of adult roots and occasionally, causes seed rot and damping-off of seedlings.
Rhizoctonia solani AG-2-2 and AG-4 also cause damping-off and root rot on soybean and edible bean crops. Thus, soil populations of R. solani can increase in fields with close rotations of bean and sugarbeet crops and result in more frequent problems with seed rot, damping-off, and root and crown rot of sugarbeet.
The only fungicides available for control of R. solani on sugarbeet are seed treatments (i.e., Captan, Chloroneb, Pentachloronitrobenzene, Thiram). These seed treatments can help control seed rot and damping-off but do not control root and crown rot. Effective, alternative fungicides are needed to provide control of seed rot, damping-off, and root and crown rot throughout the growing season. Quadris is a broad-spectrum fungicide that controls many foliar diseases caused by a wide range of fungi including Cercospora leaf spot on sugarbeet. In a 1997 field trial, an in-furrow application of Quadris was very effective in controlling seed rot and damping-off caused by R. solani AG-4 (Sugarbeet Research and Extension Reports, Vol. 28: 298-300). Quadris has not been tested for control of seed rot, damping-off, and root and crown rot of sugarbeet caused by R. solani AG-2-2.
The objectives of this research were to determine the efficacy of two rates of Quadris applied: 1) in-furrow to control seed rot and damping-off caused by R. solani AG-2-2 and 2) postemergence to control root and crown rot caused by R. solani AG-2-2.
MATERIALS AND METHODS
Separate trials were established for in-furrow and postemergence applications of Quadris. Trials were planted at the Northwest Experiment Station, University of Minnesota, Crookston on May 28, 1998. Seed of HM Shasta, treated with the fungicides Apron+Thiram at standard rates was sown (200 seeds per 30 foot row, 22 inch rows) in four-row plots with a rod row planter. Counter was applied at 1.8 pounds active ingredient per acre. Both trials were arranged in a randomized block design with four replicates. Irrigation tape was placed along the two middle rows of each plot. Data were collected on stand for the two center rows of each plot.
In-furrow trial - Inoculum (24 g of barley grains infested with R. solani AG-2-2) was distributed with the seed by the planter into the two center rows. Quadris also was applied at planting as an in-furrow treatment at 0.075 and 0.15 ounce of active ingredient per 1000 feet of row. Folicur (a fungicide that controls R. solani) was applied at 0.184 ounce of active ingredient per 1000 feet of row. Control plots (not treated with fungicide) were planted similarly, with and without R. solani added to the furrow. Plots were irrigated at 1, 3, 4, 8, and 11 days after planting with 133, 120, 72, 72, and 72 gallons per plot (gpp), respectively to maintain high soil moisture favorable for infection of seedlings by R. solani AG-2-2.
Postemergence trial - The postemergence trial was not treated with inoculum of R. solani AG-2-2 or fungicides at planting. Five weeks after planting (July 2), inoculum (24 g of barley grains infested with R. solani AG-2-2) was distributed along each of the two middle rows. Soil was raked from between the rows to cover the inoculum. Quadris and Folicur treatments (same rates as above) were applied about 4 hours later in a 7-inch band with a bicycle sprayer; plots were irrigated (48 gpp) the same day. Further irrigation was not necessary because the plots received 5.8 inches of rainfall in June.
Table 1. Effect of Quadris (applied in-furrow at planting into rows inoculated with Rhizoctonia solani AG-2-2) on stand.
Number of plants/60 ft of rowY
Rate (oz a.i./
TreatmentW 1000 ft row) InoculatedX 2½ wap 5 wap 7½ wap
Quadris 0.075 + 235 223 177
Quadris 0.150 + 224 206 189
Folicur 0.184 + 167 157 157
No fungicide - + 45 4 2
No fungicide - - 214 184 175
LSD (P=0.05)Z 44 46 50
WSeed of HM Shasta was pretreated with the fungicides Apron+Thiram at standard rates.
X The furrow was inoculated at planting with barley grains colonized by Rhizoctonia solani AG-2-2 (48 g/60 ft of row).
Y Each value is based on an average of 400 sugarbeet seeds planted/60 ft of row, four replicates on May 28, 1998; wap = weeks after planting.
ZLeast Significant Difference (LSD) value is provided, P=0.05.
RESULTS AND DISCUSSION
In-furrow trial - At 2½ weeks after planting, low stand establishment in the R. solani-inoculated plots not treated with the fungicide (Table 1) indicated that inoculum of the fungus was very active. From 2½ to 5 weeks after planting there was some decline in stand regardless of treatment. Both rates of Quadris resulted in equal and statistically (P=0.05) greater stands than the fungicide Folicur at 2½ and 5 weeks after planting, but all fungicide treatments were statistically greater than the R. solani-inoculated, no fungicide control. Both rates of Quadris also resulted in excellent stands that were equal to those attained in the noninoculated, no fungicide control.
The steady decrease in stand in the noninoculated, nonfungicide-treated plots from 2½ to 7½ weeks after planting indicates that natural inoculum of R. solani, combined with wet soil conditions, resulted in continued disease pressure (Table 1). By 7½ weeks after planting, stand for all fungicide treatments (both rates of Quadris and Folicur) and the noninoculated, nonfungicide-treated control were statistically (P=0.05) equal and greater than the R. solani-inoculated, no fungicide control. During the experiment, the fungicides Quadris and Folicur were decomposing and thus, losing effectiveness in controlling R. solani AG-2-2. The higher rate of Quadris tended to retain a higher stand than the lower rate of Quadris because decomposition of the fungicide would take longer.
Postemergence trial - At the time of application of inoculum of R. solani AG-2-2 and fungicides, sugarbeet stands were uniform across all plots (Table 2). Inoculum of R. solani AG-2-2 was effective in causing disease by 2½ weeks after inoculation and stands were very low in the inoculated, no fungicide plots. In fact, wilting of foliage was observed within 1 week of inoculation with R. solani AG-2-2. At 2½ weeks after inoculation, stands were higher and statistically (P=0.05) greater for the noninoculated, no fungicide control than for all other treatments. Both rates of Quadris resulted in statistically equal stands that were greater than Folicur and the R. solani-inoculated, no fungicide control. Folicur resulted in stands statistically lower than the Quadris treatments, but greater than the R. solani-inoculated, no fungicide control.
Table 2. Stand of sugarbeet at 2½ and 10 weeks after inoculating 5-week-old plants with Rhizoctonia solani AG-2-2 followed about 4 hours later by application (in a 7-inch band) of the fungicides Quadris and Folicur.
of plants/60 ft of rowX
TreatmentV 1000 ft row) InoculatedW At inoculation 2 ½ wai 10 wai
Quadris 0.075 + 240 173 18
Quadris 0.150 + 236 163 22
Folicur 0.184 + 242 122 15
No fungicide - + 232 39 18
No fungicide - - 249 214 84Y
LSD (P=0.05)Z ` NS 31 12
VSeed of HM Shasta was pretreated with the fungicides Apron+Thiram at standard rates.
W Inoculum (48 g barley grains colonized by Rhizoctonia solani AG-2-2/60 ft of row) was added along the row and covered with soil raked from between rows on July 2, 1998.
X Each value is based on an average of 400 sugarbeet seeds planted/60 ft of row, four replicates on May 28, 1998 and inoculated with R. solani AG-2-2 and treated with fungicides on July 2, 1998; wai = weeks after inoculation.
Y Non-inoculated, no fungicide plots were thinned to 90 plants/60 ft of row on 8/4/98; no thinning was done in R. solani-inoculated plots.
ZLeast Significant Difference (LSD) value is provided, P = 0.05; NS = treatments not significantly different.
Stands decreased in all plots from the time of inoculation until 10 weeks later because of Rhizoctonia root and crown rot caused by naturally occurring and applied inoculum of R. solani AG-2-2. By this time, both rates of Quadris, Folicur, and the R. solani-inoculated, no fungicide control had the same low stand. The noninoculated, no fungicide plots (which had been thinned to 90 plants per 60 foot of row on August 4) had the highest stand.
Plots were not harvested because of low stands at the end of the season. Although control of Rhizoctonia root and crown rot was excellent at 2½ weeks after inoculation with R. solani AG-2-2 and application of Quadris, one application of the fungicide proved inadequate to provide full-season control under conditions of severe and sustained disease pressure. Further investigation is needed to determine the number and timing of applications of Quadris for maximum control of Rhizoctonia root and crown rot of sugarbeet.
Quadris is a highly effective fungicide for controlling seed rot, damping-off and root and crown rot caused by R. solani AG-2-2, but more research is needed to determine the number and timing of applications for increased duration of control.
We thank Zeneca for providing fungicides and a grant-in-aid; Jeff Nielsen and Todd Cymbaluk, University of Minnesota, Northwest Experiment Station, Crookston, for technical support and statistical analyses; and the Sugarbeet Research and Education Board of Minnesota and North Dakota for funding in support of this research.