Bioactivity of Systemic Insecticides in Corn: Relationship to Leafhopper Vector Control and Corn Stunt Disease Incidence12

Abstract

Of seven granular systemic insecticides applied in-furrow at 1 1b per acre to corn, Zea mays L., at planting, carbofuran was the most effective for control of the leafhopper Dalbulus maidis (DeLong & Wolcott), followed in order of efficacy by aldicarb, methomyl, propoxur, phorate, disulfoton, and fenthion. Insect control was reflected in corn stunt disease incidence data which ranged from 16, 62, and 78% in carbofuran, aldicarb, and methomyl treatments, respectively, to 94-97% in the propoxur, disulfoton, phorate, and fenthion treatments, and the untreated control 77 days after planting. The efficacy of aldicarb and carbofuran applied in furrow at 0.5, 1, and 2 lb/acre at planting in a sandy loam soil at a medium moisture level was found to be rate-dependent in greenhouse tests. Carbofuran at 2 1b/acre was effective against D. maidis up to 5 weeks when leafhoppers were allowed a 2-hour feeding period on treated plants; aldicarb at this rate was effective for 3 weeks after planting. Carbofuran and aldicarb at 1 1b/acre were effective for 3 and 2 weeks, respectively, and at 0.5 1b/acre for 2 and 1 weeks, respectively. Carbofuran and disulfoton side-dressed at 1 1b/acre to one side of corn 28 days after planting were absorbed and trans located in sufficient quantities to be toxic to D. maidis between Days 2 and 4 after application when the insects were allowed to feed on the test plants for at least 8 hours. Insecticide activity was greater in leaves on the plant side above placement of the toxic ant than in leaves on the plant side opposite placement of the toxic ant. The side-dress application did not reduce the incidence of corn stunt disease compared to plants not treated with insecticide.