We compared eight weed control systems in soybeans [Glycine max (L.) Merr.] using several combinations of the herbicides trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), alachlor [2-chloro-2′,6′-diethyl-N-methoxymethyl)acetanilide], dinoseb (2-sec-butyl-,4, 6-dinitrophenol), chloroxuron [3-[p-(p-chlorophenoxy)phenyl]-1,1- dimethylurea], and linuron [3-(3,4-dichlorophenyl)-1- methoxy-1-methylurea] with or without cultivation to cultivation only and cultivation plus handhoeing. Cultivation plus handhoeing controlled the most weeds. Eight weed control systems using herbicides or herbicides plus cultivation controlled more weeds in soybeans than the system using only three cultivations. There was no significant difference in soybean yield between the system using three cultivations and six other systems using herbicides or herbicides plus cultivation. Trifluralin or alachlor applied as a preemergence treatment followed by postemergence treatments of chloroxuron, dinoseb, and linuron controlled weeds nearly as well as cultivation plus handhoeing. When dinoseb was applied repeatedly to leaves early after emergence, it severely injured soybeans, reduced soybean yield, and did not control sicklepod (Cassia obtusifolia L.). Sicklepod was the dominant weed species remaining at harvest.

The effect of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] combinations on various physiological processes was studied in order to establish a basis for the synergistic effect of this mixture on Japanese millet [Echinochloa crus-galli (L.) Beauv. var. frumentacea L.]. In contrast to atrazine, alachlor had no effect on the Hill reaction activity of isolated Japanese millet chloroplasts. When used in combination with atrazine, alachlor had no influence on the inhibitory effect of atrazine on the Hill reaction. Atrazine and alachlor combinations reduced chloroplast protein and severely inhibited chloroplast protein synthesis relative to protein synthesis by other particulate fractions. This inhibition appears to be the basis for the synergistic effect of this herbicide mixture on Japanese millet. Although the mechanism of action of the herbicide mixture is not understood, it does not seem to involve inhibition of atrazine detoxification.

Four field experiments were conducted to study the effects of row width, cultivation, soybean population, soybean cultivar, and herbicides on soybean [Glycine max (L.) Merr.] yields and control of common cocklebur (Xanthium pensylvanicum Wallr.). When the same herbicide practices were applied to all treatments, common cocklebur was controlled better in soybeans planted in 100-cm rows and grown with cultivation than in those planted in 18 or 33-cm rows and grown without cultivation. Increased soybean yields and better common cocklebur control were obtained when soybean populations were increased from 80,000 to 350,000 plants/ha. Common cocklebur reduced the yield of ‘Bragg’, one of the most competitive cultivars, 7% when grown in 100-cm rows with cultivation and 39% when grown in 33-cm rows without cultivation. The yields of six other cultivars were reduced about 20% in 100-cm rows and 32% to 52% in 33-cm rows. Cross cultivation controlled common cocklebur more effectively than did conventional cultivation in 100-cm rows, but cross cultivation was not advantageous when metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one] and bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] were applied.

Irrigation laterals PL.15.LR and S2.15W, in the Yakima Valley of Washington and the Columbia River near Paterson, Washington, were sampled for weed seeds during 1970, 1971, and 1973–74, respectively. Weekly or biweekly screenings of the water in the three systems during the irrigation season yielded seeds of 137, 84, and 77 plant species, respectively. In the same order, the total number of seeds per 254 kl of water averaged 2,220, 682, and 292 for the season. Moreover, if the seeds were evenly distributed in the average amount of water used to irrigate the land during the season, the number of seeds disseminated would average 94,500, 10,400, and 14,100 per hectare. Weed control practiced by water users along certain sections of S2.15W markedly reduced both the kind and number of weed seeds found in the water when compared with PL.15.LR on which no weed control measures were used.

Competition studies were conducted in Brazil during 1972 and 1973 between high populations (160 plants/0.1 m2 at 5 to 7 weeks after planting) of purple nutsedge (Cyperus rotundus L.) and the following vegetable crops: garlic (Allium sativum L. ‘Mineiro’), okra (Hibiscus esculentus L. ‘UFV 1152’), carrot (Daucus carota L. ‘Nantes’ and ‘Kuroda’), bush-type green bean (Phaseolus vulgaris L. ‘Topcrop’), cucumber (Cucumis sativus L. ‘Aldai’), transplanted cabbage (Brassica oleracea L. var. capitata ‘Louco’) and transplanted tomato (Lycopersicon esculentum Mill. ‘Santa Rita’). Purple nutsedge grew all year with irrigation, although growth was greater during the warm, wet season (October to March). Crop losses due to purple nutsedge competition during the entire cropping season were as follows: garlic 89%; okra 62%; two carrot cultivars, ‘Kuroda’ and ‘Nantes’ 39% and 50%, respectively; green bean 41%; cucumber 43%; cabbage 35%; and tomato 53%. Critical periods of purple nutsedge competition occurred between 3 and 13 weeks for garlic; 3 and 7 weeks for okra, cucumber and the carrot cultivar ‘Nantes’; 3 and 5 weeks for tomato and the carrot cultivar ‘Kuroda’; and at approximately 4 weeks for cabbage and green bean. Purple nutsedge competed for light in the slow-growing, non-competitive crops and for nutrients in all crops. Competition for water was reduced because the vegetables were irrigated regularly. The rate of leaf area development for a competitive crop, green bean, was similar to the rate for purple nutsedge, whereas the rate was much lower for the non-competitive okra.

The volatilities of iso and normal butyl esters of 2,4-D [(2,4-dichlorophenoxy)acetic acid] in a commercial formulation applied as thin films on pyrex and as aqueous droplets on pyrex and leaf surfaces increased directly with the available surface area/applied dose ratio (Q), and inversely with the adsorptive and absorptive characteristics of the surface, under the same conditions of temperature (39 ± 1.5 C), relative humidity (RH) (0%), geometry, airflow rate (750 ± 7 ml/min) and light. Partial pressures and rates of volatilization were computed. Herbicide in droplets below 200μ in diameter tended to volatilize faster than it penetrated, but the reverse occurred above this diameter.

Adsorption of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], terbutryn [2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine], and GS-14254 [2-(sec-butylamino)-4-(ethylamino)-6-methoxy-s-triazine] decreased on natural and limed soils as the soil pH increased to pH 8. More reduction in adsorption occurred with GS-14254 than with the other two herbicides. Increased toxicity to barley from GS-14254 was proportional to decreased adsorption by soils. Adsorption-desorption studies with Chehalis sandy loam (Cumulic Ultic Haploxeroll) indicated that extent and strength of adsorption were equivalent for GS-14254 (pKa 4.36) and terbutryn (pKa 4.32) at a soil pH of 5.20. Two soils, Boyce silt loam (pH 9.6, Cumulic Haplaquoll) and Crooked silt loam (pH 8.5, Xerolic Durorthid), adsorbed the s-triazines readily in contrast to the soils below pH 8. The high adsorption values were substantiated by the GR5 0 values on barley for atrazine and terbutryn, 10.2 and 13.2 kg ai/ha, respectively.

The uptake of 14C labeled bromacil [5-bromo-3-sec-butyl-6-methyluracil] by wheat plants (Triticum aestivum L. ‘Gaines’) grown in a Woodburn silt loam was studied at soil water potentials of −0.35 and −2.50 bars, and in solutions containing 2.0 and 4.5 μg/ml bromacil. Transpiration rate, shoot and root dry weight, and bromacil content were measured as a function of time. Bromacil uptake into the root and foliar portions of the wheat plants increased with time. At the low bromacil concentration, 70%, and at the high concentration, 42%, more bromacil was taken up by the plant at the higher soil water potential. Uptake of bromacil increased concurrently with increased transpiration of water. The bromacil concentration in the transpiration stream was greater at the −0.35 bar than at the −2.50 bar soil water potential at both bromacil application rates. Transpiration rates of the plants treated with bromacil were nearly the same after a 40-hr exposure at both soil water potentials. The rate of bromacil uptake and accumulation may be influenced by the effect of soil water potential on the apoplastic movement of water and solutes in the roots.

Cotton maintained free of annual grass and broadleaf weeds for 6 or more weeks after emergence in 1969 produced maximum yields, whereas in 1970 and 1971, 8 or more weeks of weed-free maintenance were required. Nitrogen applications at planting of 67 and 100 kg/ha did not influence the weed-free requirement of cotton in any year. Cotton yields were not reduced in 1969 when weeds were allowed to compete for 4 or 2 weeks. In 1970 and 1971 weed competition for 7 or fewer weeks did not result in yield reductions. Nitrogen did not affect the competitive relationship between cotton and weeds in 1969 and 1971. In 1970, however, cotton tolerated only 6 weeks of competition at the zero nitrogen rate, whereas it tolerated 7 weeks of competition at the 67 and 100 kg/ha nitrogen rates. Height and stem diameter of cotton were less reliable indicators of the crop-weed relationship than was yield. Neither height nor stem diameter of cotton revealed a consistent difference in the competitive relationship at the three nitrogen rates.

Soil carryover of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] following annual applications to a sorghum [Sorghum bicolor (L.) Moench] monoculture was studied by assessing sorghum yield factors as well as yields of a subsequent bioassay crop of oats (Avena sativa L.). Atrazine applications of 3.4 kg/ha or more increased sorghum injury and rates of 4.5 kg/ha and more increased seed weight and decreased sorghum stand. Sorghum recovered from early atrazine injury and stand loss and generally maintained yields. Rates of 2.2 kg/ha did not reduce sorghum yields even with repeated annual usage. There appears to be little hazard of reducing sorghum yields due to atrazine carryover in the soil from annual atrazine applications at normal rates to a clay loam or silty clay loam soil in eastern Nebraska. However, atrazine carryover will have to be a consideration if the grower plans to rotate to a susceptible crop such as oats.

Selective control of downy brome (Bromus tectorum L.) in alfalfa (Medicago sativa L.) was studied in 1971 and 1972. Herbicidal efficacy and alfalfa tolerance, yield, and percent and total protein were observed. The weed population was composed of almost 100% downy brome in 1971 and 1972. Herbicide treatments were applied early and late winter when both alfalfa and downy brome were dormant. Five herbicides afforded virtually complete downy brome control in 1971: pronamide [3,5-dichloro-N-(1,1-dimethyl-2-propynyl) benzamide] at 0.84 and 1.40 kg/ha, simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] at 1.12 kg/ha, terbacil (3-tert-butyl-5-chloro-6-methyluracil) at 0.84 kg/ha, paraquat (1–1′-dimethyl-4,4′-bipyridinium ion) at 0.56 kg/ha and cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile} at 3.4 kg/ha. All herbicide treatments reduced downy brome yields in 1972. Significantly higher alfalfa yields were closely related with lower downy brome yields. In 1972, alfalfa treated with propham (isopropyl carbanilate), cyanazine, pronamide and terbacil also was higher in second cutting yields than the control. Twelve of the 23 treatments, including all triazine herbicides, increased first harvest alfalfa protein percentage in 1972 although differences were not observed in 1971. Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)-acetanilide] spring-applied in 1971 at 5.62 kg/ha was the only treatment causing visual alfalfa injury.

The addition of 1.5 ml water or 1.5 ml 0.1 N oxalic acid solution to 2 g soil samples containing 14C-labeled herbicides increased the 14C extraction efficiencies. The employment of a modified dioxane extracting-counting solution allowed the addition of 2 ml water without causing a liquid phase separation. Extraction of benzoic acid herbicides from soil was enhanced when 5 mg oxalic acid was added to 2 g soil or when soil was acidified to pH 4.1.

Concentrations of TCA (trichloroacetic acid) were determined in irrigation water after the sodium salt formulation had been applied to the banks of dry canals at 82 kg/ha for weed control. When the canals were refilled about 5 months after treatment, maximum concentrations of TCA detected in the water ranged from 53 to 297 ppb. The concentration was highest during the first hour of waterflow. The maximum concentration increased at a rate of 26 to 30 ppb/km of canal treated, unless surface runoff or reduced flow volumes caused abnormal flows in the canals. With one exception, no TCA was detected in the water after 4 hr of flow.

Various growth regulators, carrier systems, and ammonium thiocyanate (NH4SCN) additions in combination with herbicide mixtures were evaluated for their foliar phytotoxicity to winged elm (Ulmus alata Michx.). Silvex [2-(2,4,5-trichlorophenoxy)propionic acid] and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] were more effective than the dichlorophenoxy herbicides. Additions of NH4SCN to the ester of 2,4,5-T consistently increased control. Picloram (4-amino-3,5,6-trichloropicolinic acid) was the most effective herbicide for killing the trees, and in mixtures with the phenoxy herbicides consistently produced good tree kill. No increase in 2,4,5-T activity could be attributed to additions of growth regulators, concentrated nutrient solutions, or to type of carrier system used.

Weed population shifts occurred when simazine [2-chloro-4,6-bis(ethylamino)-s-triazine], diuron [3-(3,4-dichlorophenyl)-1,1-dimethyl-urea], terbacil (3-tert-butyl-5-chloro-6-methyluracil), and dichlobenil (2,6-dichlorobenzonitrile) were applied annually for 5 years to an apple orchard. The number of brambles (Rubus sp.) and Virginia clematis (Clematis virginiana L.) plants increased with terbacil. usage. Bramble populations increased with the high rate of dichlobenil and goldenrod (Solidago sp.) increased at the low rate. The major vegetation on plots receiving amitrole (3-amino-s-triazole) was not altered from that of a mowed check. However, amitrole reduced growth of shallow planted trees. Postemergence applications of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) four times during each growing season resulted in more bare soil than was in the mowed checks at the end of the fifth growing season. Yields of apples were higher in the simazine, terbacil, and dichlobenil-treated plots than in the mowed checks. Simazine and terbacil residues did not accumulate in the upper 60 cm of soil during the study; a slight accumulation of dichlobenil appeared to occur in the surface 0 to 15-cm.

Prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] and dinoseb (2-sec-butyl-4,6-dinitrophenol) were applied in a non-phytotoxic undiluted oil carrier to sorghum (Sorghum bicolor L. ‘RS 610’), bean (Phaseolus vulgaris L. ‘Cascade’), and cucumber (Cucumis sativas ‘Wis. SMR-18’) simultaneously or separately, where prometryn treatment was followed by dinoseb at varying intervals of time. The simultaneous application of the two herbicides resulted in an additive response on all three plants, except that a slight antagonism was observed at one rate on both bean and cucumber. A synergistic response was observed when dinoseb treatment was delayed for at least 1 day on bean and cucumber and 2 days on sorghum. 14C-prometryn (14C) movement in bean leaves was not altered by simultaneous dinoseb application.

Glyphosate [(N-phosphonomethyl) glycine] was evaluated for three years as a foliar herbicide for the control of johnsongrass [Sorghum halepense (L.) Pers.]. In the greenhouse, maximum rhizome kill resulted from foliar applications of glyphosate at 1.12 to 2.24 kg/ha. In several field studies, plowing from 4 to 21 days following glyphosate application had little effect on johnsongrass control; plowing within 0.5 hr following glyphosate application resulted in less control than when plowing was delayed for 12 days. In stage of growth studies, control was better when glyphosate was applied to johnsongrass in the boot to full head stage than earlier when johnsongrass was 45 to 60 cm in height. In ‘York’ soybeans [Glycine max (L.) Merr.], glyphosate at 1.12 to 2.24 kg/ha applied 12 to 14 days prior to plowing and trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) incorporated prior to planting provided good johnsongrass control. In ‘3369A’ corn (Zea mays L.) directed postemergence applications of glyphosate provided good johnsongrass control but caused extensive crop injury.

Inhibition of growth and photosynthesis in sugarbeet (Beta vulgaris L. var. ‘USH10’) treated with desmedipham [ethyl m-hydroxycarbanilate carbanilate (ester)] was most severe between 25 and 30 C and decreased with higher or lower temperatures. Transfer of sugarbeet plants grown at temperatures from 10 to 35 C to higher temperatures after treatment increased injury and photosynthetic inhibition. Higher temperatures prior to treatment reduced injury at all posttreatment temperatures. When the temperature was changed from 25 to 40 C, inhibition was most severe immediately after treatment. Two days after treatment this 15 C temperature change did not cause additional injury. High posttreatment light intensities caused greater inhibition of photosynthesis than low light intensities.

Experiments were conducted in the growth chamber and greenhouse to determine the influence of humidity, temperature, simulated rainfall, and oil additives with bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4) 3H-one 2,2-dioxide] upon redroot pigweed (Amaranthus retroflexus L.) control. Generally, bentazon gave increased redroot pigweed control with high rather than low humidity. However, the increased weed control with high humidity was greater at 10 C than at 20 or 30 C. A simulated rainfall within 24 hr after bentazon application reduced redroot pigweed control. A simulated rainfall of 650 L/ha within 1.5 hr after bentazon application increased control of redroot pigweed, while more than 1300 L/ha simulated rainfall decreased redroot pigweed control. Emulsifiable linseed oil and petroleum oil additives to the spray reduced the detrimental effect of low humidity and simulated rainfall upon redroot pigweed control with bentazon. Emulsifiable linseed oil was more effective than petroleum oil in reducing the detrimental effect of low humidity and of simulated rainfall. However, emulsifiable linseed oil reduced the redroot pigweed control with bentazon with high humidity at 30 C compared to bentazon applied alone or with petroleum oil.

Two, 4-dichloro-6-fluorophenyl-p-nitrophenyl ether (CFNP) is similar in herbicidal property and chemical structure to nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether). CFNP inhibits the growth of the hypocotyl and young buds of germinating weeds. Henry Crabgrass (Digitaria adscendens H.B.K. Henr.) was controlled by CFNP at 0.5 kg/ha, however sunflower (Helianthus annuus L.) was tolerant to 16 kg/ha of CFNP. CFNP also effectively controlled largeseed dodder (Cuscuta indecora Choisy) which is a serious problem in sunflower. Although trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) did not control common dodder at 8 kg/ha, CFNP gave control at 0.5 kg/ha.