Preemergence Herbicides plus Postemergence Chloroxuron on Soybeans

Abstract

Greenhouse and field studies were conducted with 3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron). Tolerant soybean(Glycine max(L.) Merr.) and susceptible tall morningglory(Ipomoea purpurea(L.) Roth.) and ivyleaf morningglory(I. hederacea(L.) Jacq.) were studied with both root and foliar chloroxuron applications. Soybean tolerance to chloroxuron was reduced when treatments occurred in the unifoliate stage; greatest soybean tolerance was noted when soybeans were treated in either the cotyledonary or third trifoliage stage. Tall and ivyleaf morningglory were susceptible to chloroxuron until about 21 days of age (five true leaves), after which resistance increased. Root applications of chloroxuron were more phytotoxic than foliar applications for soybeans and both species of morningglory. In a 3-year study in the field, the following sequential herbicide treatments of either α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), 4-(methylsulfonyl-2,6-dinitro-N,N-dipropylaniline (nitralin),S-propyl dipropylthiocarbamte (vernolate), or 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) applied preemergence plus chloroxuron postemergence resulted in higher soybean yields than any single herbicide treatment. Weed control was better with the sequential combinations. All sequential combinations with chloroxuron caused soybean injury. Greatest soybean injury occurred when chloroxuron was applied in the first and second trifoliate stage than in the third trifoliate stage. Vernolate alone caused some injury in certain years.