Effect of crop growth stage on tolerance to low doses of thifensulfuron:tribenuron

Abstract

Field studies were conducted at Morden, Manitoba, in 1994 and 1995 to investigate the effect of crop growth stages on canola and sunflower tolerance to sublethal doses of thifensulfuron:tribenuron (2:1). Thifensulfuron:tribenuron at doses of 0, 0.23, 0.45, 0.9, 1.8, and 3.6 g ai ha−1plus a nonionic surfactant at 0.5% v/v were applied to canola and sunflower at the two- to three-leaf, four- to five-leaf, and six- to seven-leaf stages. Crop leaf stage at the time of application affected tolerance of both crops to thifensulfuron:tribenuron. Crop injury was lowest, and flowering, seed yield, and seed oil content were least affected when low doses of thifensulfuron:tribenuron were applied at the two- to three-leaf stage. At the highest dose, there was little practical difference among growth stages since yield of both crops was severely reduced. Producers with drift-affected canola or sunflower can expect less effect on crop yield when thifensulfuron:tribenuron injury occurs during early crop growth.