Winter applications of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) or combinations of paraquat with diquat [6,7-dihydrodipydrido (1,2-α: 2′,1′-c) pyrazinediium ion], propham (isopropyl carbanilate), or pronamide [3,5-dichloro-N-(1,1-dimethyl-2-propynyl)benzamide], usually controlled both winter annual grass and broadleaf weeds in established white clover (Trifolium repens L. ‘New Zealand,’ ‘Louisiana S-1,’ and ‘Tillman’). Diquat controlled broadleaf weeds, but was less effective than paraquat or combinations of paraquat with diquat, propham, or pronamide for grass control. Dichlobenil (2,6-dichlorobenzonitrile) controlled weeds in some experiments. Pronamide and propham usually controlled grass weeds but not broadleaf weeds. In experiments in which clover seed production differed significantly, paraquat or combinations of paraquat with propham or pronamide usually resulted in higher yields than the check. Yields increased more often where treatments included paraquat.

Cytokinins break bud dormancy and apical dominance, induce basal bulb formation, and dwarf shoot growth in purple nutsedge (Cyperus rotundus L.). Perfluidone (MBR 8251) [1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl) phenyl] methanesulfonamide] in addition to being phytotoxic, mimics the cytokinins in these aspects. This and other herbicides which have demonstrated effectiveness in nutsedge control may derive their potency from the preconditioning effects of their cytokinin activity combined with their phytotoxicity.

One-year-old and 3-month-old black walnut (Juglans nigra L.) and yellowpoplar (Liriodendron tulipifera L.) seedlings were treated with ring-labeled 14C-simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] in nutrient culture. Simazine uptake was measured and the levels of simazine and its degradation products monitored at 3, 6, and 9 days following treatment for 1-year-old seedlings and at 3, 8, and 13 days for 3-month-old seedlings. Concentration of simazine and the phytotoxic degradation product monodealkylated simazine [2-chloro-4-amino-6-(ethylamino)-s-triazine] were significantly higher in yellowpoplar than in black walnut leaves. For 1-year-old seedlings, higher concentrations of phytotoxic compounds in yellowpoplar than in black walnut were attributed to greater simazine degradation by black walnut. For 3-month-old seedlings, higher concentrations in yellowpoplar were attributed to greater simazine uptake by yellowpoplar and greater degradation in black walnut. Simazine degradation proceeded rapidly in both species and N-dealkylation was a major pathway. Monodealkylated simazine and 2-chloro-4,6-diamino-s-triazine were isolated from various tissues of black walnut and yellowpoplar. Hydroxysimazine [2-hydroxy-4,6-bis(ethylamino)-s-triazine] was found in yellowpoplar roots but not in any black walnut extracts. Two other degradation products were isolated but not identified.

Soil columns and soil thin-layer chromatography were used to evaluate the mobility of napropamide [2-(α-naphthoxy)-N,N,-diethylpropionamide] in various soils. The surface-applied herbicide did not move deeper than approximately 6 cm in a Teller sandy loam soil after a water application of 10.2 cm. The Rf values for napropamide and two reference herbicides were in the order of fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] > napropamide > terbutryn [2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine]. The mobility of each herbicide was reduced with an increase in clay and organic matter content. Carbon-14 ring labeled napropamide was used to determine the adsorption and desorption characteristics of the herbicide in various soils. The Rf values obtained with napropamide and each soil agreed with the adsorptive characteristics. Small applications of a muck soil to a sand (2%, w/w) significantly increased herbicide adsorption and decreased herbicide desorption.

Canada thistle [Cirsium arvense (L.) Scop.] and field bindweed (Convolvulus arvensis L.) were controlled in asparagus (Asparagus officinalis L. ‘Mary Washington’) fields by repeated applications of dicamba (3,6-dichloro-o-anisic acid) at 0.6 kg/ha or 2,4-D [(2,4-dichlorophenoxy)acetic acid] + dicamba at 1.1 + 0.3 or 1.1 + 0.6 kg/ha. Applications of 2,4-D + dicamba at 1.1 + 0.6 kg/ha in early May and again in mid-June controlled 97% of the Canada thistle in asparagus fields. A third application about August 1 was required to give similar control of field bindweed. Rates of dicamba exceeding 0.6 kg/ha injured the asparagus.

Selected herbicides were evaluated for control of large crabgrass [Digitaria sanguinalis (L.) Scop.] and goosegrass [Eleusine indica (L.) Gaertn.] in planted ‘Tifway’ bermudagrass (Cynodon sp.). The most effective treatment technique was sequential treatments of DCPA (dimethyl tetrachloroterephthalate) at planting followed with two applications of MSMA (monosodium methanearsonate) + 2,4-D [(2,4-dichlorophenoxy) acetic acid] which controlled 95% of the weeds and permitted bermudagrass to form a 96% ground cover in 22 weeks. Other treatments, listed in order of decreasing effectiveness were a single application of oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one], pronamide [3,5-dichloro-N-(1,1-dimethyl-2-propynyl)-benzamide] applied in two applications and MSMA + 2,4-D in two applications.

Plots were established in 1970 in the Nebraska Sandhills for the control of green sagewort (Artemisia campestris L.). Herbicides were applied in 1970; 1970 and 1971; 1970, 1971, and 1972; and 1970 and 1972. Nitrogen fertilizer at 45 kg/ha was applied in 1973. Herbicide treatments included 2,4-D amine [(2,4-dichlorophenoxy)acetic acid], 2,4-D ester, 2,4,5-T [(2,4-5-trichlorophenoxy)acetic acid], silvex [2-(2,4,5-trichlorophenoxy)propionic acid], and mixtures of picloram (4-amino-3,5,6-trichloropicolinic acid) or dicamba (3,6-dichloro-o-anisic acid) and 2,4-D amine. Herbicides were most effective for the control of broadleaf weeds when they were applied in 3 consecutive years or in alternate years. Herbicides applied only once did not effectively control broadleaf weeds. When nitrogen was applied after weed control treatments, weed production increased if herbicide applications were not effective. If weed control treatments were effective, nitrogen did not affect weed production.

Glasshouse experiments were conducted to determine the phytotoxic effect of triallate [S-(2,3,3-trichloroallyl)-diisopropylthiocarbamate] granules on oat (Avena sativa L. ‘Kelsey’). The sphere-of-influence of the granules was found to diminish rapidly with increase in the horizontal distance from the tips of the caryopses. At a distance of 10 mm from the caryopsis tip there was no significant effect on the growth of the oat seedling. The need for the granules to be in close proximity to the developing coleoptile could not be counteracted by increasing the number of granules per caryopsis once the granules were 10 mm or more from the caryopsis. These results give cause to seriously question the generally held belief that triallate disperses through the soil in a volatile phase. Extension of the first leaf and mesocotyl was inhibited much more readily by triallate than coleoptile extension, which was stimulated by a number of treatments. When granules were left on the soil surface of sub-irrigated pots the phytotoxic effect seemed to be mediated through triallate-exposure of the coleoptile tip.

Ten warm-season and six cool-season weed species were grown in the glasshouse on Hartsells fine sandy loam soil and Lucedale sandy loam soil at pH levels from 4.7 to 6.3. Growth of species varied widely in response to soil pH as measured by herbage yield. Showy crotalaria (Crotalaria spectabilis Roth), coffee senna (Cassia occidentalis L.), and large crabgrass (Digitaria sanguinalis (L.) Scop.] were highly tolerant to low pH soils. Sicklepod (Cassia obtusifolia L.), annual bluegrass (Poa annua L.), Carolina geranium (Geranium carolinianum L.), and buckhorn plantain (Plantago lanceolata L.), were medium to high in tolerance. Jimsonweed (Datura stramonium L.), tall morningglory [Ipomoea purpurea (L.) Roth], crowfootgrass [Dactyloctenium aegyptium (L.) Richter], and prickly sida (Sida spinosa L.) were medium to low in tolerance to low soil pH. Growth of Florida beggarweed [Desmodium tortuosum (Sw.) DC], redroot pigweed (Amaranthus retroflexus L.), chickweed [Stellaria media (L.) Cyrillo], common dandelion (Taraxacum officinale (Weber), and wild mustard [Brassica kaber (DC.) L.C. Wheeler var. pinnatifida (Stokes) L.C. Wheeler] was severely reduced in soils with low pH.

Cycloate (S-ethyl N-ethylthiocyclohexanecarbamate), applied by subsurface injection at 3.4 kg/ha, controlled 98 to 100% of barnyardgrass [Echinochloa crus-galli (L.) Beauv.] and 82 to 94% of common lambsquarters (Chenopodium album L.) and hairy nightshade (Solarium sarachoides Sendt.). Phenmedipham (methyl m-hydroxycarbanilate m-methylcarbanilate) at 1.1 kg/ha, applied after sugarbeets had emerged but before common lambsquarters had more than three pairs of true leaves or hairy nightshade had more than three or four true leaves, controlled the members of these species that had survived cycloate. Cycloate preconditioned sugarbeets and the surviving broadleaf weeds to injury be phenmedipham. Although applying phenmedipham following cycloate before sugarbeets had two pairs of true leaves sometimes resulted in severe crop injury, and applying it when weeds were too large resulted in incomplete weed control, in all experiments there was a period of at least 2 weeks during which application of phenmedipham killed the surviving lambsquarters and nightshade without injuring sugarbeets.

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.

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.

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.

Herbicide mobility in soils was compared by three laboratory methods. The Rf values calculated from soil thin-layer chromatography correlated closely with those obtained from soil thick-layer chromatography (r = 0.96). Herbicides leached slightly further in slotted column chromatography as compared with the other methods. The working hours required to conduct a study with each method were in the increasing order of thin-layer, thick-layer, and column chromatography. However, the thin-layer method required the longest waiting times, followed by the column and thick-layer chromatography. If radioactive herbicides are not available or obtainable, the thick-layer chromatography is simplest and quickest. The relative mobility of herbicides studied was fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] > napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] > terbutryn [2-(tert-butyl-amino)-4-(ethylamino)-6-(methylthio)-s-triazine] > trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). Less herbicide mobility was observed in heavier soil than in sandy soil.

The effect of surface corn (Zea mays L.) plant residue on weed control with atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] or alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] was studied in the field and greenhouse. Plant residue did not significantly affect weed control when herbicides were applied at recommended rates but had an increased influence on control as herbicide rates were reduced. In the greenhouse, simulated rain improved the control of velvetleaf (Abutilon theophrasti Medic.) and foxtail millet [Setaria italica (L.) Beauv.].

Studies of the differential responses of soybean [Glycine max (L.) Merr.] cultivars to bentazon [3-isopropyl-1H-2,1,3,-benzothiadiazin-(4)3H-one 2,2-dioxide] revealed slightly greater translocation and about a twofold greater foliar absorption in the sensitive cultivar ‘PI 229.342 (Nookishirohana),’ than in the tolerant cultivar, ‘Clark 63.’ Clark 63 metabolized bentazon faster than did PI 229.342. Bentazon was metabolized to unidentified polar metabolites I and II in Clark 63, and only to metabolite II in PI 229.342. The differential absorption and metabolism resulted in a tenfold greater concentration of bentazon in the treated leaflet of PI 229.342 than in that of Clark 63 at 8 days after foliar treatment. Leaflets contained similar amounts of 14C in petiole uptake studies, but no bentazon was detected in Clark 63 leaflets 24 hr after pulse treatment, whereas about 20% of the methanol-extractable 14C from PI 229.342 leaflets cochromatographed with bentazon. Metabolite I was labile to selected enzymes with β-glycosidic activity, whereas metabolite II was unaffected. Bentazon concentrations of 30 to 50 μM inhibited O2 evolution about 50% in isolated chloroplasts from the two cultivars. Differential bentazon metabolism appears to be the main cause of the differential responses of these soybean cultivars to bentazon.

Tolerance of corn (Zea mays L.) to cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile} and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] was compared when grown in Conover sandy loam soil. Reductions in seedling dry weight were obtained under both low and high soil moisture following preemergence and postemergence applications of cyanazine allowed to contact both plants and soil. During periods of active plant growth high soil moisture is favorable for rapid root uptake of cyanazine which causes injury to corn.

MSMA (Monosodium methanearsonate) applied postemergence at 4.5, 6.7, or 9.0 kg/ha controlled wild oat (Avena fatua L.) in new plantings of Kentucky bluegrass (Poa pratensis L. ‘Pennstar’) and in perennial ryegrass (Lolium perenne L. ‘Reveille,’ ‘Pennfine’). MSMA at 4.5 kg/ha was almost as effective as the higher rates in controlling wild oat. MSMA at 2.2 kg/ha was less effective in some experiments. Visual injury to the perennial grasses was negligible. Satisfactory grass stands developed at all MSMA rates. Perennial ryegrass seed yields were higher than the untreated check in most experiments when MSMA was applied at 4.5, 6.7, or 9.0 kg/ha before the grass reached the boot stage. When MSMA was applied after the ryegrass reached the boot stage, some of the treatments reduced ‘Reveille’ perennial ryegrass seed production.

The effect of time, flow rate, and temperature on the volatilization of technical grade n-butyl ester of 2,4-D [(2,4-dichlorophenoxy)acetic acid] in a closed air-flow system was evaluated. The amount of ester volatilized was linear with time, at constant temperature and air flow. Volatility increased approximately 8-fold when the temperature was increased from 30 C to 50 C. At 30 C, volatility increased with each doubling of air flow rate from 0.86 nmole/cm2 per hr at 14 L/hr to 1.62 nmole/cm2 per hr at 57.6 L/hr. The effects of temperature, flow rate, and the relationship between vapor pressure and rate of volatilization were also analyzed. The system provided a simple and quantitative method for determining the relative volatilities of both technical and formulated herbicides.