Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Research was conducted during the growing seasons of 1981 and 1982 in Baton Rouge, Louisiana, to evaluate the response of itchgrass and soybean yield to weed control practices used in conventional soybean culture. Trifluralin ((alpha),(alpha),(alpha)-triflouro-2,6-dinitro-N,N = -dipropyl-p-toluidine) (preplant incorporated) at 1.8 kg/ha, alachlor {2-chloro-2',6'-diethyl-N-(methoxymethyl)acetanilide} (preemergence) at 2.4 kg/ha, or no soil applied herbicide, followed by zero, one or two overtop applications of diclofop as the methyl ester at 1.2 kg/ha {2-{4-(2,4-dichlorophenoxy)phenoxy}propanoic acid} were applied in cultivated and noncultivated areas to determine effects on seedling emergence, density, height, standing biomass and seed production of itchgrass {Rottboellia exaltata (L.) L.f.} at soybean {Glycine max (L.) Merr. 'Forrest'} maturity. Although cultivation stimulated the emergence of itchgrass seedlings, its repetitive use resulted in a reduction of late emerging seedlings. Cultivation had no effect on the density, height, standing biomass or seed production of single plants in the soybean row but increased soybean yield compared to no cultivation. The average weight, number of tillers and branches, and seed production of single itchgrass plants were greater in the trifluralin treatments when compared to the no soil applied or postemergence herbicide application treatment. Trifluralin only, trifluralin plus one diclofop application and all treatments with two applications of diclofop resulted in good to excellent control with or without cultivation. Soybean yield was inversely proportional to itchgrass density and standing biomass. Soybean yield and net income were increased after trifluralin or trifluralin plus one application of diclofop versus no soil or postemergence herbicide application. A second application of diclofop did not result in further increases in the trifluralin treatments. One or two applications of diclofop after treatments of alachlor or no soil applied herbicide increased yields, but net income attributable to weed control did not increase as a result of a second application of diclofop.