IMIDACLOPRID FORMULATION AND SOIL PLACEMENT EFFECTS ON COLONIZATION BY SWEET-POTATO WHITEFLY (HOMOPTERA, ALEYRODIDAE) - HEAD SIZE AND INCIDENCE OF CHLOROSIS IN LETTUCE

The effects of imidacloprid formulation and soil placement on coloniza tion by sweetpotato whitefly, Bemisia tabaci (Gennadius), at 3 plant g rowth stages of lettuce, Lactuca sativa L., were evaluated in experime ntal 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 p lacement had a significant effect on sweetpotato whitefly colonization in lettuce throughout the experimental period. Sweetpotato whitefly d ensities on lettuce varied at each plant stage relative to depth of pl acement within the lettuce seed bed. Applications made to the soil sur face and at 4.0-cm subseed furrow, followed by irrigation, provided th e most consistent control of sweetpotato whitefly nymphs in small plot s and in on-farm lettuce plots. These imidacloprid soil treatments als o prevented reductions in head size and incidence of leaf chlorosis as sociated with sweetpotato whitefly colonization in lettuce. Our data s uggest that incorporation of imidacloprid into the upper 3-4 cm of soi l below the seed furrow is optimal for absorption and translocation by lettuce roots. Imidacloprid soil treatments may provide a more enviro nmentally suitable and effective alternative to control of sweetpotato whiteflies in lettuce than is currently possible with foliar insectic ide treatments.