CHARACTERIZATION OF RHIZOCTONIA SPP CAUSING DISEASE OF LEAFY SPURGE IN THE NORTHERN PLAINS

Diseases of leafy spurge (Euphorbia esula) occurred widely in Montana and were also found in Colorado and North Dakota during the spring and summer of 1991. Rhizoctonia solani AG-4 was isolated from mature leafy spurge plants showing crown rot and necrotic root buds, whereas binucleate Rhizoctonia-like fungi were isolated from stem cankers and blights. Pathogenicity of the Rhizoctonia strain to leafy spurge was tested by inoculating cut stems or by planting mature crowns or seed in a greenhouse soil mix artificially infested with the fungi. Five of six R. solani AG-4 strains, but only two of eight binucleate strains, were pathogenic on stems. All strains of R. solani AG-4 caused root and crown rot and preemergence damping-off of spurge, and four of eight binucleate strains induced damping-off. All R. solani AG-4 strains were from Montana.