Field efficacy of fungicides for management of sheath blight and narrow brown leaf spot of rice

Sheath blight (caused by Rhizoctonia solani AG1-IA) and narrow brown leaf spot (NBLS, caused by Cercospora janseana) are among the most important diseases affecting rice production in Texas and in other regions in the southern United States. Strobilurin fungicides have been used extensively to manage these two diseases, especially sheath blight. Unfortunately, heavy reliance on use of fungicides with a single mode of action has induced the development of the strobilurin-resistant isolates of R. solani AG-1 IA in the U.S. NBLS, once considered a minor disease in the U.S, is growing in its occurrence and severity, while little scientific information is available on NBLS management. This created an urgent need for identifying other effective fungicides with different modes of action. A 6-year field study was conducted on rice to evaluate the efficacy of newly registered and unregistered fungicides in comparison to common fungicides for management of sheath blight and NBLS diseases. Single applications of the fungicides containing azoxystrobin, propiconazole, azoxystrobin plus propiconazole, trifloxystrobin plus propiconazole, fluxapyroxad, pyraclostrobin, flutolanil and antibiotics (validamycin and kasugamcyin) were made at the late booting stage. Sheath blight and NBLS severities were rated prior to harvest. All the fungicide treatments were effective in reducing sheath blight severity compared to the untreated control in each year. Propiconazole and fluxapyroxad were more effective in reducing NBLS than other fungicides. Along with reduced sheath blight and NBLS severities, fungicide-treated plots had higher yields than untreated plots.