There are currently no broadleaf herbicides registered in Canada for use in
common buckwheat (Fagopyrum esculentum Moench.). Greenhouse and field stud
ies were conducted from 1994 to 1997 at Morden and Brandon, Manitoba, to in
vestigate potential herbicide treatments for buckwheat when cultural method
s fail to control broadleaf weeds. Dose-response studies conducted in the g
reenhouse showed that buckwheat tolerance to desmedipham was three to five
times greater than that of volunteer canola (Brassica napus L. and B. rapa
L.), lamb's-quarters (Chenopodium album L.), redroot pigweed (Amaranthus re
troflexus L.) and wild mustard (Sinapis arvensis L.). A separate experiment
showed that buckwheat cultivars did not differ in tolerance to desmedipham
. Another greenhouse study demonstrated that low dosages of bentazon caused
severe injury in buckwheat. In field studies, 500 to 700 g a.i. ha(-1) of
desmedipham effectively suppressed the annual broadleaf weed biomass in buc
kwheat without reducing seed yields. At a low dosage of 300 g ai. ha(-1) of
desmedipham there were no yield losses even though no weed biomass reducti
on was evident. Imazamethabenz at 150 to 250 g a.i. ha(-1) and metribuzin a
t 140 and 210g a.i. ha(-1) severely injured buckwheat and usually reduced y
ields. 2,4-D at 140 g a.i. ha(-1) suppressed weed biomass, but caused sever
e injury and often reduced buckwheat yield. At 70 g a.i. ha(-1), 2,4-D supp
ressed weed growth as effectively as the higher dosage with less visual inj
ury, but sometimes reduced buckwheat yields. Thus, desmedipham is the most
promising postemergence broadleaf herbicide for use in common buckwheat.