Broccoli, cabbage and cauliflower tolerance to sulfonylurea herbicides

Limited information exists on cole crop tolerance to post-emergence (POST) applications of sulfonylurea (SU) herbicides under Ontario growing conditions. Broccoli, cabbage and cauliflower were evaluated for tolerance to ethametsulfuron-methyl, foramsulfuron, nicosulfuron, rimsulfuron, thifensulfuron-methyl, and triflusulfuron-methyl in nine separate experiments conducted from 2002 to 2004. Each of the SU herbicides was applied at the proposed and twice the proposed use dose in broccoli, cabbage and cauliflower. Ethametsulfuron-methyl did not cause visual injury, and did not reduce head weight or yield in all nine trials conducted. Foramsulfuron, nicosulfuron, rimsulfuron and thifensulfuron-methyl caused unacceptable injury (greater than 10%) at the proposed use dose of each herbicide. Injury symptoms included stunting, twisting of the petioles, and malformed, chlorotic leaves. Foramsulfuron and nicosulfuron caused complete death of broccoli, cabbage and cauliflower at the proposed use dose of each of these herbicides. Injury was severe enough to prevent head production of broccoli, cabbage and cauliflower at twice the proposed use dose of rimsulfuron and thifensulfuron-methyl. Though heads were formed in the triflusulfuron–methyl treatments, head weight and yields were reduced at the proposed use dose of this herbicide. Ethametsulfuron-methyl is the only herbicide to which broccoli, cabbage and cauliflower possessed an acceptable level of tolerance.