SOYBEAN (GLYCINE-MAX) RESPONSE TO WEED INTERFERENCE AND RHIZOCTONIA FOLIAR BLIGHT (RHIZOCTONIA-SOLANI)

Field studies evaluated response of soybean to Rhizoctonia foliar blig ht (RFB) disease in combination with varying densities of common cockl ebur, hemp sesbania, or johnsongrass. Soybean plants at both V10 and R 1 growth stages were not inoculated or inoculated with suspensions con taining equal concentrations of Rhizoctonia solani AG-1 IA and IB myce lia. Intensity of RFB was rated weekly beginning at V1 soybean growth stage, and data were used to determine area under disease progress cur ves. Intensity of RFB was greater in 1993 than in 1994. When averaged across weed species and weed densities, soybean yield in 1993 was redu ced 18% in plots inoculated with R. solani compared with those not ino culated. Intensity of RFB, however, did not differ between inoculated and noninoculated plots in 1994. Interactions between R. solani and we ed density for RFB intensity and yield were not significant either yea r. Soybean yields in 1994, however, were reduced by hemp sesbania and johnsongrass in inoculated plots. Soybean maturity was delayed both ye ars when hemp sesbania was present.