Effect of Plant Growth Regulators Under Short-Season Conditions on Pink Bollworm Populations, Cotton Yields and Defoliation

Abstract

Plant growth regulators (PGR's) [thidiazuron (Dropp®) N-phenyl-N' -1,2,3-thiadiazol -5 ylurea, 50% wettable powder, Nor-Am Agricultural Products, Inc., Naperville, IL, and ethephon (Prep®) a- chloroethyl phosphonic acid Rhone - Poulenc Ag Co., Research Triangle Park NC] were applied to reduce late- season fruiting forms as a source of host material for developing overwintering PBW populations. Combinations of ethephon and thidiazuron or thidiazuron alone were more effective than ethephon alone for reducing late -season immature green bolls. None of the PGR's alone or in combination affected yields. Highest rates of defoliation occurred after applications of thidiazuron. The data suggest that temperature thresholds for highest plant growth regulator activity occur.