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The Influence of Winter Legume Cover Crops on Soilborne Plant Pathogens and Cotton Seedling Diseases. C. S. ROTHROCK, Department of Plant Pathology, University of Arkansas, Fayetteville 72701. T. L. KIRKPATRICK, Department of Plant Pathology; and R. E. FRANS and H. D. SCOTT, Department of Agronomy, University of Arkansas, Fayetteville 72701. Plant Dis.79:167-171. Accepted for publication 21 October 1994. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0167.

The influence of winter legume cover crops on soilborne plant pathogens and seedling diseases of cotton was examined at two locations over 2 yr. The Clarkedale site was a long-term cover crop experiment established in 1972. The Lewisville site was established in a production field with a history of cotton monoculture. Soil populations of Thielaviopsis basicola and isolation frequency of this pathogen from cotton seedlings were reduced following a hairy vetch cover crop compared with winter fallow at Clarkedale, the only site with moderate to high soil populations of this pathogen. Isolation of Rhizoctonia solani from cotton seedlings and soil populations of Rhizoctonia spp. at planting were increased following hairy vetch compared with winter fallow at Lewisville. A similar trend was found for Rhizoctonia spp. following hairy vetch at Clarkedale. Soil populations of Pythium spp. were greater at both locations following a legume cover crop compared with winter fallow, however, no difference among cover crop treatments were found for isolation frequency of this genus from seedlings. The other cover crop treatments (common vetch, hairy vetch plus rye, or crimson clover plus rye) were intermediate between winter fallow and hairy vetch in their influence on pathogen populations and isolation frequency. Bacterial and fungal populations were greater in the cropping system containing a hairy vetch cover crop compared with winter fallow at Clarkedale. The influence of winter legume cover crops on the seedling disease complex depended on the prevalent pathogens at each location. Winter legumes do not appear to increase the risks of cotton seedling diseases sufficiently to deter their use in reducing soil erosion and providing nitrogen to a subsequent cash crop, and can reduce the risk of black root rot.

Keyword(s): Gossypium hirsutum. Vicia villosa, Chalara elegans, Thanatephorus cucumeris