Rates and application timings of postemergence herbicides for wild oat control in spring wheat and barley were evaluated at Crookston, MN, from 1994 to 1996. Diclofop, imazamethabenz, and fenoxaprop plus MCPA plus thifensulfuron plus tribenuron were applied to one- to three-leaf wild oat; and difenzoquat, imazamethabenz, fenoxaprop plus MCPA plus thifensulfuron plus tribenuron, and fenoxaprop plus 2,4-D plus MCPA were applied to four- to five-leaf wild oat at 1/2 ×, 3/4 ×, and 1 × rates. Wild oat response to herbicide rate and timing was similar in wheat and barley. Wild oat control with 1/2 × rates generally was less than that with 3/4 × rates, which was lower than or similar to that with 1 × rates. Wild oat biomass was often reduced less with 1/2 × rates than 1 × rates. However, reducing herbicide rates generally did not influence grain yields or net economic return. Grain yields and net economic return were generally greater in herbicide-treated plots than in the nontreated control.

Diphenylether herbicides may be viable options for postemergence (POST) control of common waterhemp in soybean. A 2-yr field research project was conducted to determine whether common waterhemp control is influenced by application timing and rate of acifluorfen, fomesafen, and lactofen. Common waterhemp control was 9, 9, and 8% greater 7, 14, and 21 d after treatment, respectively, after the early postemergence (EPOST) application timing compared with the POST application timing. Lactofen provided greater common waterhemp control than did acifluorfen or fomesafen, and only the highest application of lactofen provided greater than 85% common waterhemp control 21 d after POST application. No significant differences in common waterhemp dry weight were determined among the three rates of acifluorfen, fomesafen, and lactofen applied EPOST. The highest application rates of fomesafen and lactofen reduced common waterhemp dry weight more than did the lowest application rates applied POST. The highest application rate of fomesafen also reduced common waterhemp dry weight more than did the intermediate application rate. Single degree of freedom contrasts indicated that all diphenylether herbicides reduced common waterhemp dry weight more than did imazethapyr.