Control of volunteer flax in wheat

Abstract

Volunteer flax (Linum usitatissimum) can interfere with harvesting operations in cereals, especially at high flax densities. Field experiments were conducted in 1996 and 1997 at Morden and Brandon, Manitoba, Canada, to evaluate tribenuron and thifensulfuron plus tribenuron (2:1) alone and in mixtures with 2,4-D, quinclorac, flamprop-methyl and fluroxypyr for their ability to control volunteer flax in spring wheat. Volunteer flax cvs. NorLin and CDCTriffid, a transgenic, sulfonylurea-tolerant cultivar, were cross-seeded to plots of spring wheat cv. AC Domain. Herbicides were applied at rates recommended for their use in spring wheat, when wheat was at the three- to four-leaf stage and flax was 5–8 cm tall. When left uncontrolled, volunteer flax reduced wheat yields by up to 27%. Tribenuron and thifensulfuron plus tribenuron (2:1) provided poor control of NorLin flax and almost no control of Triffid flax. Flax density was not reduced, but biomass was reduced to some extent, more for NorLin than for Triffid. The addition of 2,4-D to the tank-mixes of the sulfonylurea herbicides had some effect on flax biomass reduction but results were not consistent. Wheat yields were reduced in three of the five field trials. The other herbicides controlled NorLin and Triffid flax equally well. Quinclorac at 100 and 200 g a.i. ha−1 provided consistently good flax control, generally without yield loss to the wheat crop. Fluroxypyr plus 2,4-D and fluroxypyr plus clopyralid plus MCPA were as effective as quinclorac, but were tested only in 1 yr. Flamprop-methyl reduced flax biomass and provided good control in 1997, but control was poor in 1996 and resulted in wheat yield losses. Recently, quinclorac has been registered for use against volunteer flax in spring wheat. Key words: Volunteer flax, sulfonylurea resistant flax, spring wheat, control, yield loss