Interaction of Fungicides, Herbicides, and Planting Date with Seedling Disease of Cotton Caused by Rhizoctonia solani AG-4. Samy M. Moustafa-Mahmoud, Department of Plant Pathology, University of Georgia Coastal Plain Experiment Station, Tifton 31793-0748. Donald R. Sumner, M. M. Ragab, and Mona M. Ragab. Department of Plant Pathology, University of Georgia Coastal Plain Experiment Station, Tifton 31793-0748; and Department of Plant Pathology, Cairo University, Giza, Egypt. Plant Dis. 77:79-86. Accepted for publication 18 September 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0079.

In field experiments with seedling disease of cotton (Gossypium spp.) caused by Rhizoctonia solani anastomosis group (AG)-4 in Egypt and in Georgia, recommended rates of the herbicides norflurazon, pendimethalin, fluometuron, prometryn, fomesafen, and oxyfluorfen significantly affected the efficacy of the fungicides tolclofos-methyl, pencycuron, carboxin, flutolanil, metalaxyl, and chloroneb on the basis of percentage of plant stand 7–42 days after planting. Also, the efficacy of three experimental combinations of fungicides and two fungicide combinations sold commercially (copper oxyquinolate + carboxin and pentachloronitrobenzene + metalaxyl) was reduced. All herbicides caused visible damage to cotton plants in Tifton loamy sand soil in Georgia but not in the silty loam soil in Egypt. The most rapid recovery from herbicide damage and the least reduction in efficacy of fungicides were observed with herbicide norflurazon. In Georgia, the efficacy of fungicides was evaluated with no herbicides for four planting dates between 29 March and 2 May. Planting on 12 and 19 April did not affect the efficacy of the fungicides chloroneb, flutolanil, pencycuron, tolclofos-methyl, metalaxyl, or pentachloronitrobenzene, but it significantly reduced the percentage of stand with carboxin. Efficacy of all fungicides was reduced by delaying planting until 2 May (in warm, wet soil, 21–28 C) or planting early (29 March) in cool, wet soil (14–24 C).