WILD MUSTARD (BRASSICA KABER) RESISTANCE TO ETHAMETSULFURON BUT NOT TO OTHER HERBICIDES

In 1993, a wild mustard population growing in a canola crop near Wetas kiwin, AB was poorly controlled by ethametsulfuron after only one prev ious use of the herbicide. Controlled environment experiments were con ducted to compare the response of this suspected resistant population (R) with that of a known susceptible population (S) collected near Veg reville, AB to increasing rates of ethametsulfuron, metsulfuron, chlor sulfuron, thifensulfuron, HOE 075032, imazamethabenz, imazethapyr, met ribuzin, and 2,4-D. The R wild mustard population was highly resistant to ethametsulfuron, slightly resistant to low rates of metsulfuron bu t not resistant to any of the other herbicides tested. This suggests t hat the mechanism of resistance may differ from that reported for othe r sulfonylurea and imidazolinone herbicides. Since resistance was docu mented after only 2 yr of ethametsulfuron use, the initial frequency o f resistance to this herbicide in wild mustard populations may be very high. Dry weight of untreated plants did not differ significantly bet ween the S and R populations suggesting little or no differences in co mpetitiveness between them.