IN-FURROW APPLICATION OF QUADRIS FOR CONTROL OF RHIZOCTONIA DAMPING-OFF OF SUGARBEET
Carol E. Windels and Jason R. Brantner
Associate Professor of Plant Pathology and Research Fellow
Northwest Experiment Station, University of Minnesota, Crookston
Rhizoctonia solani (=R. solani) causes seedling stand establishment problems on sugarbeet. Two strains of R. solani (AG-2-2 and AG-4) are involved in damping-off (a sudden collapse and death of young seedlings), but AG-4 is the most frequent pathogen. Rhizoctonia solani AG-2-2 also causes root and crown rot of adult sugarbeet plants, but AG-4 is not pathogenic to older roots.
Rhizoctonia solani AG-2-2 and AG-4 also cause damping-off and root rot on soybean and edible bean crops. Thus, Rhizoctonia damping-off of sugarbeet occurs most frequently in fields where there is a close rotation of bean and sugarbeet crops.
The only fungicides available for control of R. solani on sugarbeet are seed treatments (i.e., Captan, Chloroneb, PCNB, Thiram). Effective, alternative fungicides are needed because production of soybean and other bean crops is expanding on land rotated with sugarbeet. Quadris is a broad-spectrum fungicide that controls many foliar diseases caused by a wide range of fungi. The product also shows activity against certain soilborne pathogens, including R. solani.
The purpose of this research was to evaluate three rates of Quadris, applied in-furrow at planting, for control of damping-off caused by Rhizoctonia solani AG-4 and for effects on sugarbeet yield and quality.
MATERIALS AND METHODS
The trial was established at the Northwest Experiment Station, University of Minnesota on June 18, 1997. A late planting date was selected to ensure that soil was warm, which favors infection of sugarbeet by R. solani AG-4. Seed of HM Shasta, treated with the fungicides Apron + Thiram at standard rates, was sown (300 seeds per 30 foot row, 22 inches between rows) with a rod row planter. The planter simultaneously distributed 32 g (=1.1 ounces) of inoculum of R. solani AG-4 (grown on sterile barley grains for 3 weeks) into the two center rows of each 4-row plot. Quadris also was applied at planting as an in-furrow treatment at the equivalent of 0.01, 0.02, and 0.04 ounces of active ingredient per 1000 feet of row in the two middle rows. The control was planted in the same fashion, except that no Quadris was added to the furrow. Each treatment was replicated four times in a randomized block design.
After planting, irrigation tape was placed on both sides of the two middle rows of each plot and watered with about 193 gallons of water per plot. Further irrigation was unnecessary because about 3.3 inches of rain fell in the next 6 days. The two center rows were thinned to an equivalent of 150 plants per 100 feet of row on July 14, 1997 because it was determined the plots should be harvested. Herbicides, insecticides and fungicides (for control of Cercospora leaf spot) were applied, as needed.
Data were collected for emergence on the two center rows of each plot. The two center rows were harvested on October 22, 1997. Data were obtained for the number of marketable-sized roots and for sugarbeet yield and quality.
RESULTS AND DISCUSSION
Poor sugarbeet stands in the control indicate that inoculum of R. solani AG-4 was active and provided a good test for the effectiveness of Quadris. At 23 days after planting, the three rates of Quadris resulted in stands that were statistically the same (P=0.05), but greater than the untreated control (Table 1). There was a trend for the 0.02 oz rate of Quadris to result in the best stand.
Examination of harvested roots revealed no root rot (data not shown), nor was it observed during the season. This is not surprising since R. solani AG-4 causes seed rot and damping-off, but not root rot of adult roots. The number of plants in the control (stand was not thinned because of scarcity of plants) decreased between 3 weeks after planting and harvest (Table 1). Many seedlings that emerged in the control were somewhat unthrifty because they were infected by R. solani AG-4 and thus, were too weak to survive to harvest.
Yields were low for all treatments because of the late planting date and excess nitrogen, but they did indicate differences among treatments. Number of harvested roots, tons per acre, and recoverable sucrose were the same for the three rates of Quadris and were statistically greater (P=0.05) than the control (Table 1). There were no significant differences in percent sucrose among the three rates of Quadris or the control. The 0.01 and 0.02 oz rates of Quadris resulted in the lowest percentage of loss to molasses compared to the 0.04 oz rate and the control, which were the same (Table 1). Overall, the 0.02 oz rate of the product tended to offer the best stand and highest sugarbeet yield and quality compared to the 0.01 and 0.04 oz rates.
Quadris is a highly effective fungicide in controlling damping-off caused by R. solani AG-4.
We thank Zeneca for providing the product and a grant-in-aid; Jeff Nielsen for technical support and statistical analyses; American Crystal Quality Lab in East Grand Forks for sugar analyses; and the Sugarbeet Research and Education Board of Minnesota and North Dakota for funding in support of this research.
1997 Sugarbeet Research and Extension Reports. Volume 28, pages 298-300