Quackgrass (Elytrigia repens) management in flax (Linum usitatissimum)

Field studies were conducted at the Agriculture and Agri-Food Canada, Resea rch Centre, Morden, Manitoba from 1992 to 1996 to evaluate quackgrass manag ement in flax with several graminicides applied at annual and perennial gra ss rates, and with preharvest glyphosate applied after postemergence gramin icides. Ah graminicides at both application rates reduced quackgrass biomas s. However, at annual grass rates, clethodim and sethoxydim were sometimes less effective at controlling quackgrass than quizalofop and fluanifop-P. T here was some evidence that annual-rate applications of sethoxydim can resu lt in increased quackgrass regrowth in the second year. Flax seed yields we re not affected by the use of graminicides at annual grass rates compared w ith perennial grass rates, whereas untreated (weedy checks) flax had yield losses of up to 67% compared with weed-free plots. The use of preharvest gl yphosate reduced second-year regrowth of quackgrass by half or more, compar ed with no preharvest glyphosate treatment. Where preharvest glyphosate had been applied, the weedy checks tended to have markedly less quackgrass reg rowth than where graminicide treatments had been applied in the spring. Thi s suggests that use of spring-applied graminicides may reduce the effective ness of preharvest glyphosate to control quackgrass. However, use of a post emergence graminicide is often necessary to control annual grasses as well as quackgrass because flax yield is seriously affected by uncontrolled weed growth. A second experiment was conducted to compare the efficacy of liqui d and dry formulations of glyphosate applied with water and 28-0-0 fertiliz er as carriers. The three glyphosate formulations applied at 0.9 kg a.e. ha (-1) were equally effective at reducing quackgrass biomass in flax without yield loss, but at 0.45 kg a.e. ha(-1), the liquid formulation was sometime s less effective. There was no consistent evidence that the use of liquid u rea/ammonium nitrate fertilizer as a carrier, rather than water, affects th e performance of either liquid or dry glyphosate formulations.