Tolerance of common buckwheat (Fagopyrum esculentum) to low rates of 2,4-Dand MCPA

Field studies were conducted from 1995 to 1997 at Morden and Brandon, Manit oba, Canada, to evaluate the effect of crop growth stage at application on common buckwheat (Fagopyrum esculentum Moench.) tolerance to low rates of 2 ,4-D amine, MCPA amine and the sodium salt of MCPA. Each formulation was ap plied at 140 g a.i. ha(-1) to common buckwheat at the two- to three-leaf, f our- to five-leaf, and six- to eight-leaf stages. Levels of buckwheat injur y and seed yield loss were very similar for the three phenoxy herbicide for mulations. Although early-season crop injury was severe, injury was often l ess, and crop recovery from injury greater, when herbicide was applied at t he two-leaf stage than at the four-leaf or six-leaf stage. When herbicide w as applied at the two-leaf stage, a significant yield reduction occurred in only one of the five trials. However, buckwheat seed yield decreased when phenoxy-herbicide application was delayed past the two-leaf stage. If low a pplication rates of phenoxy herbicides to early stage buckwheat are effecti ve in suppressing weed growth, then this treatment may enable the crop to o ut-compete weeds without sustaining yield losses in most years.