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Interactions of Herbicides and Nematicides with Root Diseases of Turnip Grown for Leafy Greens. Donald R. Sumner, Assistant Professor, Department of Plant Pathology, University of Georgia; Norman C. Glaze, Plant Physiologist, Agricultural Research Service, U. S. Department of Agriculture, Coastal Plain Station, Tifton, GA 31794. Phytopathology 68:123-129. Accepted for publication 7 July 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-123.

The effect of three herbicides and two nematicides on root diseases of turnip grown for leafy greens was studied in a greenhouse and in environmental chambers. Soils were artificially infested with Rhizoctonia solani, Pythium spp., Fusarium solani, Fusarium oxysporum, and Colletotrichum sp. or were naturally infested field soils. Root diseases were caused primarily by Pythium spp. (mostly P. irregulare), Rhizoctonia solani, Fusarium solani, and F. oxysporum in naturally infested soils. Plant stands and foliage weights were decreased and root disease indices (RDI) were increased most by treatments with O-ethyl S, S-dipropyl phosphorodithi-oate (ethoprop), ethoprop + dimethyl tetrachlorotere-phthalate (DCPA), and 2,4,-dichlorophenyl-p-nitrophenyl ether (nitrofen). In some tests DCPA and a, a, a-trifluoro-2,-6-dinitro-N,, N-dipropy1-p-toluidine (trifluralin) also increased the RDI and decreased foliage weight. Ethoprop + trifluralin and 1,2,-dibromo-3-chloropropane (DBCP) did not increase the RDI. Pythium spp. were isolated most frequently from seedlings grown in soil treated with ethoprop + DCPA. Populations of Pythium spp. and F. solani were negatively correlated with plant stands in naturally infested soils. Temperature did not influence pesticide-root disease interactions.

Additional keywords: Fusarium roseum ‘Equiseti’.