SOYBEAN CULTIVAR REACTION AND ROW WIDTH EFFECT ON SCLEROTINIA STEM ROT

The response of soybean (Glycine max (L.) Merr.) cultivars to Scleroti nia stem rot, caused by Sclerotinia sclerotiorum, was assessed in repl icated field trials in 1985-1987 and 1990 to obtain information relati ng to control of the disease. In 1986 and 1987, there were differences (P = 0.01) in disease incidence among 19 indeterminate cultivars. Cul tivar differences in disease incidence were partially related to matur ity (R2 = 0.67 in 1986; R 2 = 0.37 in 1987) with earlier-maturing cult ivars having less disease. Cultivars differed (P = 0.01) in the number of sclerotia produced per diseased plant and per square meter in 1986 and 1987. In a test conducted in 1990 there were differences (P = 0.0 5) in disease incidence among 14 determinate lines. In three tests in 1985-1986, row spacings of 23, 45 and 69 cm had no significant effect on the incidence of white mold in the cultivars Maple Arrow, Evans, S1 346 and Corsoy 79. Yield loss from stem rot may be reduced by planting cultivars that are more resistant, earlier maturing and more tolerant to lodging. This practice would also result in fewer sclerotia to ser ve as primary inoculum in future years.