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Root Diseases of Snapbean and Southern Pea in Intensive Cropping Systems. Donald R. Sumner, Associate Professor, Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton, GA 31794; A. W. Johnson(2), Norman C. Glaze(3), and Clyde C. Dowler(4). (2)(3)(4)Nematologist, Plant Physiologist, and Agronomist, Agricultural Research Service, U. S. Department of Agriculture, respectively, Coastal Plain Experiment Station, Tifton, GA 31794. Phytopathology 68:955-961. Accepted for publication 9 December 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-955.

Root diseases of snapbean and southern pea were studied in whole plots of cropping systems of snapbean-soybean-cabbage, turnip-corn-snapbean, turnip-peanut-snapbean, and turnip-cucumber-southern pea-turnip. Each cropping system was repeated each year for 4 yr. Subplots were treated with a nematicide. O-ethyl S, S dipropyl phosphorodithioate (ethoprop), or nontreated, and sub-subplots were treated with herbicides, ααα-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine + 2-sec-butyl-4,6-dinitrophenol (trifluralin + di-noseb) or nontreated. Pythium spp. (primarily P. irregulare) were isolated more frequently than other fungi from spring snapbean, and Rhizoctonia solani and cultures of Fusarium solani were isolated more frequently than other fungi from fall snapbean. The fungus most frequently isolated from southern pea was R. solani. Root diseases of snapbean were more severe in the fall than in the spring, but there were no differences between the two cropping systems in the amount of root disease in fall snapbean. Root diseases of southern pea were most severe, and southern pea yields were the lowest in the 4th yr of the study. Treating soil with ethoprop resulted in a significant (P = 0.05) increase in root disease severity in three spring crops of snapbean and one crop of southern pea, but treating soil with ethoprop did not influence severity of root disease in fall snapbean. Herbicide treatments occasionally reduced but never increased root disease severity. Soil populations of total F. solani increased in the snapbean-soybean-cabbage system and soil populations of Pythium spp. increased in the turnip-peanut-snapbean system. Total populations of F. solani and Pythium spp. frequently were the lowest in herbicide-treated soils, but treating soil with ethoprop rarely influenced populations of the soil fungi measured.

Additional keywords: Phaseolus vulgaris, Vigna unguiculata.