THE INFLUENCE OF WINTER LEGUME COVER CROPS ON SOILBORNE PLANT-PATHOGENS AND COTTON SEEDLING DISEASES

The influence of winter legume cover crops on soilborne plant pathogen s and seedling diseases of cotton was examined at two locations over 2 yr. The Clarkedale site was a long-term cover crop experiment establi shed in 1972. The Lewisville site was established in a production fiel d with a history of cotton monoculture. Soil populations of Thielaviop sis bosicola and isolation frequency of this pathogen from cotton seed lings were reduced following a hairy vetch cover crop compared with wi nter fallow at Clarkedale, the only site with moderate to high soil po pulations of this pathogen. Isolation of Rhizoctonia solani from cotto n seedlings and soil populations of Rhizoctonia spp. at planting were increased following hairy vetch compared with winter fallow at Lewisvi lle. A similar trend was found for Rhizoctonia spp. following hairy ve tch at Clarkedale. Soil populations of Pythium spp. were greater at bo th locations following a legume cover crop compared with winter fallow ; however, no differences among cover crop treatments were found for i solation 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. Th e influence of winter legume cover crops on the seedling disease compl ex depended on the prevalent pathogens at each location. Winter legume s do not appear to increase the risks of cotton seedling diseases suff iciently to deter their use in reducing soil erosion and providing nit rogen to a subsequent cash crop, and can reduce the risk of black root rot.