MUSTARD TOLERANCE TO CLOPYRALID APPLIED ALONE OR WITH ETHAMETSULFURON

Mustard is a drought-tolerant crop well adapted to the Brown and Dark Brown soils of the Prairies; however, lack of broad-leaved weed contro l limits production. Two field studies were conducted at Indian Head, Saskatchewan and Lethbridge, Alberta to determine the response of brow n and oriental mustard (Brassica juncea (L.) Coss), and yellow mustard (B. hirta Moench) to clopyralid. Clopyralid was applied at 0.10, 0.15 , 0.20, 0.30, 0.60 kg a.i. ha(-1) at the 4- or 10-leaf stage in one ex periment. The other was a factorial experiment of clopyralid at 0.10, 0.20, and 0.30 kg a.i. ha(-1) with ethametsulfuron at 0.01, 0.02, and 0.03 kg a.i. ha(-1). Clopyralid applied at 0.15 kg a.i. ha(-1), the lo west rate at which it is registered for weed control in canola, result ed in brown mustard yield reductions of 21%, oriental mustard yield re ductions of 23% and yellow mustard yield reductions of 9% over 5 site years. This rate of clopyralid applied with ethametsulfuron reduced br own, oriental and yellow mustard yield by 30, 33 and 8%, respectively. Oil content was also reduced by clopyralid. Clopyralid cannot be used for weed control in mustards.