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Title: Optimum Timing of Pre-Plant Applications of Glyphosate to Manage Rhizoctonia Root Rot in Barley

Author
item BABIKER, E - Washington State University
item HULBERT, S - Washington State University
item SCHROEDER, K - Washington State University
item Paulitz, Timothy

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2010
Publication Date: 3/20/2011
Citation: Babiker, E.M., Hulbert, S.H., Schroeder, K.L., Paulitz, T.C. 2011. Optimum Timing of Pre-Plant Applications of Glyphosate to Manage Rhizoctonia Root Rot in Barley. Plant Disease. 95:304-310.

Interpretive Summary: Rhizoctonia root rot can cause severe disease losses in wheat. One way to manage this disease is to reduce the greenbridge before planting. The greenbridge is living grassy weeds or crop volunteer that allow the fungus to survive between crops. Growers remove this greenbridge with herbicide applications. But this can increase disease if done too soon beforem planting. The timing of herbicide sprayout is crucial, but growers do not know the optimal time to spray. In 3 years of field trials, we tested out different times, and developed a model based on a sigmoidal function, to predict the best time to spray out. The optimum time varied between 2-4 weeks before planting, depending on the year.

Technical Abstract: Rhizoctonia root rot, caused by Rhizoctonia solani AG-8 and R. oryzae, is considered one of the main deterrents for farmers to adopt reduced tillage systems in the Pacific Northwest. Because of the wide host range of Rhizoctonia spp., herbicide application before planting to control weeds and volunteer plants is the main management strategy for this disease. To determine the effect of time interval periods between glyphosate applications and planting date (spray-out intervals) on the severity of Rhizoctonia root rot disease of barley, field experiments were conducted in 2007, 2008 and 2009 in a field naturally infested with a high level of both R. solani and R. oryzae. Crop volunteer and weeds were allowed to grow over the winter and plots were sprayed out with glyphosate at 42, 28, 14, 7 and 2 days prior to planting. Significant increases in plant height, length of the first true leaf, and number of healthy seminal roots were associated with a decrease in disease rating and number of infected seminal roots, as the spray-out interval increased. Yield and the number of seminal roots did not show a response to spray-out interval. The activity of R. solani declined over time in all treatments after planting of barley. The spray-out intervals required to reach 80% and 90% of the maximum response (asymptote) were determined to be 11 to 27 days and 13 to 37 days, respectively. These times are the minimum spray-out intervals required to reduce disease severity and increase seedling health in the following crop.