Effects of Sequential Herbicide Treatments on Weeds and Soybeans

Sequential herbicide treatments of 3-[p-(p-chlorophenoxy)-phenyl]-1,1-dimethylurea (chloroxuron) withS-propyl dipropylthiocarbamate (vernolate) controlled weeds early in the season in soybeans (Glycine max(L.) Merr. ‘Dare’ or ‘Bragg’) better than when chloroxuron was applied in sequence with either α,α,α-trifluoro-2,6-dinitro-N,Ndipropyl-p-toluidine (trifluralin) or 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin). The control of weeds late in the season was enhanced with split applications of 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) or 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) when applied to plots previously treated with chloroxuron as early postemergence and trifluralin, nitralin, or vernolate applied preplant. In 1969 nitralin injured soybeans, and reduced stands and seed yields significantly more than trifluralin or vernolate. In 1970 sequential treatments of prometryne with chloroxuron and vernolate were more phytotoxic to soybeans than were the same postemergence treatments when applied with nitralin and trifluralin.