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Published online by Cambridge University Press: 12 June 2017
R230, an isolate of Rhizoctonia solani anastomosis group 5 from leafy spurge, caused root and crown rots on leafy spurge when inoculated via soil in greenhouse experiments. The fungus grew through soil over a wide range of matric potentials (–0.01 to −1 MPa). When applied to leafy spurge foliage, the fungus blighted young adventitious shoots, but not mature stems. Foliar infection required high relative humidity. Mycelial growth on plant surfaces stopped at below 92% relative humidity. Pathogenicity of R230 was not limited to leafy spurge. The fungus caused stem and foliar lesions on all crops tested (alfalfa, smooth bromegrass, corn, Kentucky bluegrass, soybean, tall fescue, and wheat) when plants were kept under high humidity. It reduced seedling emergence and survival in soybean, Kentucky bluegrass, and tall fescue. R230 also caused a foliar blight on spotted spurge. The potential for R230 to damage crops will limit application of the fungus to noncultivated areas and to sites where it is endemic.