Impact of transplanting date and insecticide control practices on the incidence of tomato spotted wilt virus and insect pests in flue-cured tobacco
Field studies were conducted in Georgia on flue-cured tobacco, Nicotiana tabacum L., during 1991 and 1992 to evaluate the effects of transplanting date and six insecticide control practices on the abundance of thrips, primarily Frankliniella fusca (Hinds), and tobacco aphids, Myzus nicotianae Blackman. The effects on the incidence of spotted wilt, caused by thrips-vectored tomato spotted wilt virus, and on the yield and quality of cured tobacco also were examined. Thrips populations were higher on tobacco transplanted in late March or mid-April than on tobacco transplanted in late April in 1991, but no transplanting date effects were observed in 1992. Weekly foliar sprays of acephate with or without a transplant-water treatment of acephate were effective in reducing the seasonal population densities of thrips. There were, however, no differences in the incidence of spotted wilt among the six insecticide control practices used to manage thrips in 1991. Only weekly foliar sprays reduced the incidence of spotted wilt in 1992. Transplanting date had no consistent effect upon spotted wilt infection, with higher incidence of spotted wilt in the earlier plantings in 1991 and in the later plantings in 1992. Transplanting date did not affect the seasonal population densities of aphids either year. All of the thrips control practices reduced aphid populations. There was a higher yield of cured leaves in the early-transplanted tobacco, but there were no differences among the six insecticide control treatments. Neither transplanting date nor thrips control treatments affected tobacco quality. It appears that transplanting date and the use of certain transplant-water and foliar insecticide treatments to manage thrips populations are not effective, economical, or environmentally sound methods of reducing spotted wilt in flue-cured tobacco.