Types of Rhizoctonia Foliar Blight on Soybean in Louisiana

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Abstract
Twenty locations in southern and central Louisiana were surveyed in 1987 and 1988 to determine the etiology of Rhizoctonia foliar blights of soybean (Glycine max). Web blight caused by Rhizoctonia solani anastomosis group 1, intraspecific group IB (AG-1 IB), was the major type in Louisiana in both years. Aerial blight caused by isolates of R. solani AG-1 IA, previously considered the only type in the state, was also found. No isolate of AG-1 IC was found. Isolates of AG-1 IA and AG-1 IB could be differentiated on the basis of cultural characteristics on water agar and potato-dextrose agar. Maximum production of microsclerotia in the field occurred from late July through August. Low numbers of microsclerotia produced by R. solani AG-1 IB were observed on plants at earlier and later soybean growth stages. Thanatephorus cucumeris, the teleomorph of the pathogen, was also observed during late July and August.