Effect of Insecticide Treatments and Environmental Factors on Thrips Populations, Plant Growth and Yield of Cotton

Field experiments were conducted in 1997–1999 in Washington Co., NC, to examine how cotton, Gossypium hirsutum, is affected by thrips species composition and abundance, environmental factors, and insecticide applications. Populations of adult and juvenile thrips were monitored in seedling cotton treated with insecticide applications of either imidacloprid as a seed treatment, acephate as a foliar spray, or aldicarb applied in-furrow. The number of plants per 3.05 row-m, location of the first fruiting branch, number of open bolls per 1.52 row-m, yields, accumulated degree-d 60′s (DD60′s), and accumulated rainfall were recorded each year the studies were conducted. Aldicarb and acephate provided better thrips control than did imidacloprid in all 3 yrs. Thrips species ratios differed among years. In 1997, the aldicarb treatment resulted in a better “earliness profile” (lower fruit set and more early opening bolls) than either acephate or imidacloprid, while in 1998 and 1999 there were few differences in these plant parameters. In 1997, all insecticide treatments resulted in statistically higher yields compared with the untreated check. Accumulated DD60′s were consistently higher in 1998 and 1999 than in 1997 after the first thrips sampling date. Cumulative rainfall appeared to be inversely associated with juvenile thrips populations.