Field studies were conducted for four consecutive years to determine if repeated applications of trifluralin (preplant incorporated), metolachlor (preemergence), and fluazifop (postemergence) herbicides alone or combined could be utilized in soybean to effectively control grass weed populations and maintain optimum yield in an irrigated environment where metribuzin plus dinoseb (preemergence) and 2,4-DB plus linuron (postemergence) were used as a standard weed control system. After repeated applications each year, all treatments maintained similar yields that were no different from yields obtained from the standard system. Grass weed infestation did not increase significantly in the treatment that received only the standard weed control herbicides over the duration of the study.

Field experiments were conducted during 1981 to 1984 to evaluate paraquat for weed control in alfalfa established for less than one year. Treatments were applied in March to alfalfa up to 4 cm tall and/or after cuttings to alfalfa up to 10 cm tall. Weeds were up to 20 cm tall. Paraquat applied in March controlled common chickweed and shepherd's-purse in some experiments. It did not control birdsrape mustard when applied after cuttings. Paraquat suppressed growth of perennial broadleaf weeds and grasses and reduced pressure from annual grasses in some experiments. March treatments generally did not increase, but sometimes decreased alfalfa yields. Paraquat applied after cuttings did not affect alfalfa yields in the majority of the experiments.

Experiments were conducted in each of two seasons to determine possible effects of diclofop, difenzoquat, dinoseb, and mecoprop on the incidence of take-all disease and grain yield of winter wheat. All of the herbicides, especially mecoprop, reduced incidence of take-all. Treatments increased grain yields the first year but not the second, compared to the inoculated weed-free control. None of the herbicides tested increased incidence or severity of take-all disease in either of the two seasons. The technique of inoculating disease-free soil was successful in obtaining uniform and reproducible incidence of disease.

The effects of oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] were studied on electron transport and phosphorylation in isolated spinach (Spinacia oleracea L.) chloroplasts and on the response of green bean (Phaseolus vulgaris L. ‘Spartan Arrow’) to applications of oxyfluorfen alone or in combination with other herbicides. Coupled non-cyclic electron transfer and phosphorylation through photosystems I and II (H2 O å methyl viologen) were inhibited about 30% and 55%, respectively, by 10−4 M oxyfluorfen. Photosystem II-linked phosphorylation with dimethylbenzoquinone (2,5-dimethyl-p-benzoquinone) as the electron acceptor (H2 O å DMQ) was completely inhibited by 10−4 M oxyfluorfen. Photosystem II electron transport with dimethylbenzoquinone as the electron acceptor was inhibited 60% by 10−4 M oxyfluorfen, whereas photosystem I electron transport with 2,6-dichlorophenol indophenol as electron donor (DCIPH2 å MV) was not susceptible to oxyfluorfen inhibition. Photosystem I-linked phosphorylation and the accompanying electron transport supported by durohydroquinone electron donation (DQH2 å MV) were inhibited about 50% by 10−4 M oxyfluorfen, whereas cyclic phosphorylation was not inhibited at that concentration. Increased conductivity of a solution that contained leaf discs taken from green beans treated with various combinations of foliar-applied herbicides was a measure of membrane damage caused by the herbicides, and revealed that oxyfluorfen has a different site of action than do photosynthesis inhibitor and bipyridilium herbicides. Oxyfluorfen plus dinoseb (2-sec-butyl-4,6-dinitrophenol) injury to green beans was additive, but the two herbicides did not have the same site of action. Oxyfluorfen did not appear to inhibit electron transport in chloroplasts at herbicidal rates, nor was it dependent on electron transport for activation.

The influence of manure and herbicide applications on weed-free fieldbeans (Phaseolus vulgaris L.) and root rot of fieldbeans was studied during 1978 and 1979 at Scottsbluff, Nebraska. Rates of cattle feedlot manure used were 0, 30000, 56000, 112000, or 168000 kg/ha. Preplant herbicide treatments used were alachlor [2-chloro-2′6′-diethyl-N-(methoxymethyl)acetanilide] at 3.4 kg/ha, EPTC (S-ethyl dipropylthiocarbamate) at 3.4 kg/ha, EPTC + trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 2.2 + 0.6 kg/ha, or dinoseb (2-sec-butyl-4,6-dinitrophenol) at 6.7 kg/ha. Manure rates of 56000 kg/ha or higher reduced fieldbean yields both years, but did not increase electrical conductivity or soil exchangeable sodium enough to explain these yield reductions. In 1978, but not in 1979, height and yield of weed-free fieldbeans were reduced by EPTC, EPTC + trifluralin, and alachlor treatments. A significant interaction between manure and herbicide treatments was not detected and none of the treatments increased the severity of root rot in either year.

‘Forrest’ soybean [Glycine max (L.) Merr.] infested with entireleaf morningglory [Ipomoea hederacea (L.) Jacq. var. integriusula Gray] were treated in the field with three postemergence herbicides, dinoseb (2-sec-butyl-4,6-dinitrophenol), sodium salt of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, and 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid]. Foliar nitrogen (N) loss, transpiration, and CO2 equilibrium concentrations were measured from 4 to 148 h after treatment. In morningglory foliar N loss was increased by dinoseb, decreased by acifluorfen, and first increased and then decreased by 2,4-DB treatments. Transpiration in this weed species was decreased by all three herbicides. In soybean, N loss was increased and transpiration decreased with dinoseb; acifluorfen did not affect either activity; and 2,4-DB decreased both processes during one sampling period. In both plant species dinoseb increased the CO2 equilibrium concentration within 4 h after treatment. Treatments with acifluorfen and 2,4-DB initially increased the CO2 concentration in morningglory with major increases noted at the onset of chlorosis 52 h after treatment. In soybean, some significant decreases in CO2 equilibrium concentrations occurred with the lowest rate of all three herbicides.