Imidacloprid formulation and soil placement effects on colonization by sweetpotato whitefly (Homoptera: Aleyrodidae): Head size and incidence of chlorosis in lettuce

The effects of imidacloprid formulation and soil placement on colonization by sweetpotato whitefly, Bemisia tabaci (Gennadius), at 3 plant growth stages of lettuce, Lactuca sativa L., were evaluated in experimental and commercial lettuce plots in 1993-1994. We also evaluated the effects of imidacloprid treatments on yield response and incidence of chlorosis associated with sweetpotato whitefly control. Imidacloprid placement had a significant effect on sweetpotato whitefly colonization in lettuce throughout the experimental period. Sweetpotato whitefly densities on lettuce varied at each plant stage relative to depth of placement within the lettuce seed bed. Applications made to the soil surface and at 4.0-cm subseed furrow, followed by irrigation, provided the most consistent control of sweetpotato whitefly nymphs in small plots and in on-farm lettuce plots. These imidacloprid soil treatments also prevented reductions in head size and incidence of leaf chlorosis associated with sweetpotato whitefly colonization in lettuce. Our data suggest that incorporation of imidacloprid into the upper 3-4 cm of soil below the seed furrow is optimal for absorption and translocation by lettuce roots. Imidacloprid soil treatments may provide a more environmentally suitable and effective alternative to control of sweetpotato whiteflies in lettuce than is currently possible with foliar insecticide treatments.