Effects of Repeated Applications of Herbicides on Soybeans

Abstract

Repeated postemergence treatments of 3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron), 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron), or 2-sec-butyl-4,6-dinitrophenol (dinoseb) can be applied to soybeans (Glycine max (L.) Merr.) without severe injury to the foliage throughout the growing season. However, multiple treatments of 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) resulted in more foliar injury early in the season than from similar treatments of chloroxuron, linuron, or dinoseb. Chlorotic veination appeared in the upper leaves of soybeans treated with prometryne late in the season, and injury was greater from multiple applications than from a single application. Chloroxuron and dinoseb resulted in stem injury which increased with repeated applications. Seed yields were lower from plots treated with repeated applications of prometryne compared with untreated plots or plots treated with a single application. Multiple applications of chloroxuron, linuron, or dinoseb did not affect seed yields. Soybean stands were significantly lower in 1 year from three or four applications of linuron and four applications of prometryne compared with fewer applications of each herbicide. Seed quality was best in dinoseb-treated plots and poorest in prometryne-treated plots regardless of the number of applications.