Field studies were conducted for 4 yr to investigate the effects of tillage and herbicide programs on weed control and wheat (Triticum aestivum L. ‘Potomac’ in 1981 and ‘Wheeler’ from 1982 to 1984) grain yields in a wheat-soy bean [Glycine max (L.) Merr.] double-crop rotation. Predominant weed species were common chickweed [Stellaria media (L.) Vill. # STEME], corn chamomile (Anthemis arvensis L. # ANTAR), and annual bluegrass (Poa annua L. # POAAN) at the onset of research and cheat (Bromus secalinus L. # BROSE) and soft brome (Bromus mollis L. # BROMO) at the conclusion of the study. Control of all species was excellent with conventional tillage and no-till plus nonselective herbicides but was significantly less with no-till without nonselective herbicides and with minimum tillage. After 4 yr, maximum wheat grain yields were significantly higher in conventional- than in minimum- or no-till systems.

Greenhouse studies determined the dose-responses of cheat, downy brome, Japanese brome, jointed goatgrass, and winter wheat to preplant-incorporated MON 37500 and its residual effects on kochia. Concentrations of MON 37500 up to 60 ppbw did not affect winter wheat. MON 37500 did not prevent weed emergence, but increasingly inhibited weed growth as the dose was increased up to about 20 ppbw. GR50 values were 16, 16, 11, and 31 ppbw for cheat, downy brome, Japanese brome, and jointed goatgrass, respectively. Japanese brome was more susceptible than cheat or downy brome, and jointed goatgrass tolerated two to three times more MON 37500 than the Bromus species. Plant dry weights of kochia seeded after removal of the winter annual grasses decreased with increasing initial MON 37500 concentrations up to 20 ppbw. Kochia density was influenced by which winter annual grass was grown previously.

The methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} mixed with soil at 1, 2, and 3 ppmw reduced the growth of Bromus species in the greenhouse as follows: downy brome (Bromus tectorum L. ♯ BROTE) more than Japanese brome (Bromus japonicus Thunb. ex Murr. ♯ BROJA) more than cheat (Bromus secalinus L. ♯ BROSE). The decrease in herbicide effect (decay) over time was described better using a second-order equation than a first-order equation. Plant response-herbicide dose relationships were described best with a cubic polynomial equation.