Aggregate Sheath Spot of Rice in California. P. S. Gunnell, Research Assistant, Department of Plant Pathology, University of California, Davis 95616 . R. K. Webster, Professor, Department of Plant Pathology, University of California, Davis 95616. Plant Dis. 68:529-531. Accepted for publication 15 February 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-529.

Rhizoctonia oryzae-sativae, a binucleate Rhizoctonia sp., is the causal organism of aggregate sheath spot of rice in California. Recent increase in incidence and severity of the disease has paralleled an increase in the use of semidwarf cultivars by growers. Symptoms of the disease are very similar to those of sheath blight of rice caused by R. solani in the southern United States. The fungus is the first reported binucleate Rhizoctonia sp. pathogenic on a gramineous host in the United States that is not an R. cerealis isolate.