CORESTA Congress, Paris, 2006, PPOST 11

Impact of early-season thrips exclusion and suppression on the incidence of spotted wilt in flue-cured tobacco

University of Georgia, Dept. of Plant Pathology, Tifton, GA, USA.
Incidence in flue-cured tobacco protected in early-season with thrips exclusion (cages) or thrips suppression (weekly acephate insecticide applications with or without an imidacloprid tray trench treatment). TSW is a serious economic threat to tobacco production in Georgia, USA, and is spread by tiny insects in the order Thysanoptera (thrips). There were fewer TSW symptomatic plants observed when plants were covered with thrips exclusion cages for 6 weeks following transplanting. Plant height, leaves per plant and total leaf weight per plant were similar for TSW symptomatic plants compared to non-symptomatic plants when the plants were caged for 6 weeks. This lack of plant growth response was primarily due to the late-season initiation of TSW symptoms (10-12 weeks after transplanting) once the cages were removed. Height, leaves and weight per plant were lower in the plants expressing TSW symptoms when the plants were either uncaged or caged 2 or 4 weeks after transplanting, due to the early onset of TSW symptoms (4-8 weeks after transplanting). Weekly acephate insecticide sprays for 2 or 4 weeks after transplanting reduced thrips populations for up to 5 weeks after transplanting while the 6 weekly sprays had lower thrips populations for up to 8 weeks. TSW was lower in both the 4 and 6 weekly acephate treatments than in the untreated. A tray drench application of imidacloprid also reduced thrips populations in early season plus lowered the percentage of TSW compared to no imidacloprid. The tobacco thrips, Frankliniella fusca (Hinds), was the predominate thrips species on tobacco foliage, although low numbers of other thrips were observed. The imidacloprid tray drench treatment and 6 weekly acephate foliar sprays also had lower densities of the tobacco-adapted form of Myzus persicae (Sulzer) aphids throughout the season.