WEED-CONTROL AND HERBICIDE TOLERANCE IN A COMMON VETCH-OAT INTERCROP

Field studies were conducted over 3 yr in central Spain to investigate the tolerance of common vetch and oat to some preemergence herbicides and their effects on weed control, forage yields, and botanical compo sition of the forage mixture. Pendimethalin was the only herbicide tha t injured common vetch. Pronamide and pronamide plus diuron injured oa t by affecting plant emergence. Prevalent weed species were fumitory, henbit, and wild buckwheat. All herbicides provided more than 90% cont rol of fumitory and most herbicides except pronamide provided more tha n 90% control of henbit relative to the untreated check. Wild buckwhea t stands were reduced by isoxaben (68%), linuron (40%), prometryn (69% ), pronamide (86%), and pronamide plus diuron (61%). More than 90% con trol of prostrate knotweed was achieved with isoxaben, pronamide, and terbutryn. Pronamide and pronamide plus diuron reduced forage yields a nd increased vetch in the forage. The untreated vetch and oat monocrop treatments showed the competitive advantage of oat over vetch and wee dy species.