Effects of Seed Treatment, In-Furrow Sprays, and Herbicides Treatments on Charcoal Rot of June-Planted Soybean, 2007

Authors: CANADAY, CRAIG - UNIV. OF TENNESSEE; Mengistu, Alemu

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2008
Publication Date: 3/25/2008
Citation: Canaday, C.H., Mengistu, A. 2008. Effects of Seed Treatment, In-Furrow Sprays, and Herbicides Treatments on Charcoal Rot of June-Planted Soybean, 2007. Plant Disease Management Reports. 2:14

Interpretive Summary: Charcoal rot is a disease of soybean that causes significant yield losses in the United States and around the world. Currently, no resistance variety is available and efforts to manage charcoal rot through adjusting planting dates, crop rotation, planting densities and irrigation have not been successful. The effects of seed treated with chemical and biological fungicides to control the death of young plants due to the charcoal rot disease of soybean were assessed. The highest number of healthy plants were obtained from a combination seed treatment that included the chemical fungicides mefenoxam and fludioxonil plus the biological fungicide Bacillus subtilis MBI 600. This treatment also had the least amount of above ground plant death and had the tallest plants. Dying plants collected for identification were infected with the charcoal rot organism and occasionally with another fungus (mold) called Rhizoctonia. The highest yields were obtained from fungicide seed treatments that included chloroneb and mefenoxam, with or without thiabendazole, and the mefenoxam, fludioxonil and B. subtilis combination. Death of young soybean plants due to charcoal rot disease may be reduced using these fungicide seed treatments.

Technical Abstract: Evaluation of chemical and biological fungicides to control charcoal rot of soybean was conducted in a field planted annually to soybean or snap bean since 2002 with moderate to high seedling disease losses to charcoal rot. Seed treatment slurries were created by adding distilled water to the test materials. A split-plot design was used. Main plots consisted of differences in the application of Dual II Magnum applied either pre-plant incorporated or as a pre-emergence herbicide. Subplots consisted of seed treatments applied to AG4403 soybeans, a charcoal susceptible cultivar . Irrigation was applied with a lateral boom system. Pre-emergence damping-off losses were estimated by subtracting from planted seed the number of healthy plants and post-emergence losses. The test was harvested and data were subjected to analysis of variance. There were no significant interactions between the main plot and subplot treatments. Main plots receiving the pre-plant incorporation treatment application of Dual II Magnum had more pre-emergence damping-off (P = 0.05), more post-emergence damping-off (P = 0.0001), lower healthy stands (P = 0.03), shorter plants (P = 0.0001), and lower yields (P < 0.0001) than main plots receiving the pre-emergence application. There were significant differences in subplot treatments to pre-emergence damping-off (P = 0.02) and healthy stand (P = 0.02). Highest healthy stands were obtained with a combination seed treatment that included mefenoxam + fludioxonil (Apron Maxx RTA) + Bacillus subtilis MBI 600 (Integral). This treatment also had the least amount of post-emergence damping-off and the tallest plants, though not significantly different from other treatments. Representative damped-off plants collected for pathogen identification were infected with M. phaseolina and occasionally also with R. solani. The highest yields were with seed treatments that included chloroneb + mefenoxam (Catapult XL), with or without thiabendazole (LSP), and the mefenoxam + fludioxonil + B. subtilis combination. Our study indicates that stand reduction resulting from seedling damping off due to charcoal rot may be reduced using fungicide seed treatments.