Effects of directed fungicides sprays and potash form on charcoal rot of soybeans

Authors: CANADAY, CRAIG - UNIVERSITY 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 directed fungicides sprays and potash form on charcoal rot of soybeans. Plant Disease Management Reports. 2:15.

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 directed fungicide sprays and potash application to control the death of young plants due to the charcoal rot disease of soybean were assessed. Fungicide sprays appeared to have no effect on charcoal rot in this test. However, there was a notable decrease in stand loss with sulphate potash. This study suggests that soybean growers should not consider spraying fungicide for managing or controlling charcoal rot.

Technical Abstract: Evaluation of 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. Treatments were applied on 18 Jul at 60 psi and on 7 Aug at 80 psi using a high-pressure hydraulic sprayer and two DGTJ60-11002VS nozzles/row directed towards the base of the plants in ca. 33 gal water/A. A split-plot design was used. Main plots consisted of different forms of potash fertilizer, applied either as muriate of potash (0-0-60) or as sulfate of potash (0-0-50) on 12 Jun at 100 lb K2O/A. Subplots were fungicides applied to two 20-ft-long rows spaced 30 in. apart on a cultivar AG4403 soybean, a charcoal susceptible cultivar. Treatments were applied at 60 to 80 psi using a high-pressure hydraulic sprayer directed towards the base of the plants. Irrigation was applied with a lateral boom system. Healthy stands and dead plants were recorded. Stand losses were estimated by subtracting the healthy stand from the earlier healthy stand then adding the number of dead plants in taken in Oct. Plant senescence ratings were recorded, and data were subjected to analysis of variance. There were fourteen days in Aug when air temperatures were 100 degrees Fahrenheit or higher. Weather was often very warm and dry - ideal for charcoal rot. Fungicide sprays appeared to have no effect on charcoal rot in this test. There were no significant effects on plant stand or yield due to subplot treatment. No differences in treatment phytotoxicity were observed. Main plots receiving sulfate of potash however, had significantly higher yields than those receiving muriate of potash (32.4 versus 28.6 bu/A; P = 0.01). There was also a notable decrease in stand loss with the sulfate of potash (10.0 versus 14.2%; P = 0.08).