Effect of Root Diseases and Nematodes on Yield of Corn in an Irrigated Multiple-Cropping System with Pest Management

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Abstract
Corn was planted each of 6 yr in an annual multiple-cropping system of turnip-corn-cowpea with four types of soil pest management [Georgia, USA]. Treatments were 1) broadcast soil fumigation with 98% methyl bromide + 2% chloropicrin (MBR-CP) each fall or winter; 2) broadcast soil fumigation with 20% methyl isothiocyanate + 80% chlorinated C3 hydrocarbons (DD-MENCS) each fall + maximum pest control with nonvolatile nematicides, herbicides and insecticides; 3) nonvolatile nematicides, herbicides and insecticides used for an intermediate level of pest control; and 4) one herbicide and cultivation used as needed on each crop for a minimum level of weed control. Root diseases of corn were caused primarily by Pythium aphanidermatum, P. arrhenomanes, Rhizoctonia solani AG-4, a sterile white basidiomycete, and Qhoma terrestris. Soil fumigation reduced root disease severity significantly in 5 of 6 yr and increased grain yield an average of 7.5% (0.94 t/ha). Populations of Meloidogyne spp., Paratrichodorus minor, and Pythium spp. and root disease severity ratings were correlated negatively with yield.