Studies were conducted to test if dicamba reduces haloxyfop herbicidal activity and to determine if this interaction by auxin-type herbicides or bentazon was caused by preventing the haloxyfop-induced inhibition of acetyl-CoA carboxylase (ACCase). Addition of dicamba at concentrations of 2.17 or 4.34 mM reduced haloxyfop activity on tall fescue shoots. Haloxyfop at 14 to 20 μM inhibited the activity of ACCase in cell-free extracts from tall fescue by nearly 50%. Dicamba did not prevent the inhibitory effect of haloxyfop on ACCase activity in these cell-free enzyme preparations. Dicamba alone at concentrations as high as 3.2 mM had no significant effect on the in vitro activity of the enzyme. Bentazon concentrations up to 10 mM did not prevent haloxyfop inhibition of ACCase activity. Bentazon alone or mixed with haloxyfop significantly inhibited ACCase activity at bentazon concentrations starting at 1 mM with near 40% inhibition at 10 mM. of the numerous possible explanations for the interference of dicamba or bentazon with haloxyfop action, interaction directly at the enzyme level appears to have been eliminated.

Primary root cells from five dinitroaniline-resistant (R) and three susceptible (S) goosegrass biotypes from North Carolina and South Carolina were observed by transmission electron microscopy to determine whether resistance was associated with changes in cell wall formation. Cell wall malformations were found in some cells from two of the R-biotypes and in one of the S-biotypes. Malformations consisted of partially deposited cell walls and the inclusion of cell wall material in the cytoplasm. Some of the affected cells also had abnormal, lobed nuclei and malformed mitochondria. There seems to be little or no correlation between dinitroaniline resistance and cell wall malformations.

Inhibition of net photosynthesis of jointed goatgrass and downy brome protoplasts by metribuzin and its ethylthio analog (ethyl-metribuzin) was greater at 25 than at 10 C. As temperature increased from 10 to 25 C, the concentration of ethyl-metribuzin required to inhibit net photosynthesis 50% (I50) decreased by a factor of 3.5 and 4.3, respectively, in jointed goatgrass and downy brome. I50 values for metribuzin decreased by a factor of 1.5 and 2.5 in jointed goatgrass and downy brome, respectively, for the same 15 C increase in temperature. Based on I50 values at 10 C, metribuzin was nine times more inhibitory than ethyl-metribuzin in jointed goatgrass and eight times more inhibitory in downy brome. At 25 C, metribuzin was only 4.7 and 3.9 times more inhibitory than ethyl-metribuzin in jointed goatgrass and downy brome, respectively. Thus, cold temperatures reduced the activity of ethyl-metribuzin more than metribuzin. The activity of both herbicides was reduced less in protoplasts of jointed goatgrass than in protoplasts of downy brome over the 15 C range.

Photosynthetic productivity parameters were determined for mayweed chamomile, a troublesome annual weed of the cropping systems in the Pacific Northwest. At a photosynthetic photon flux density of 1800 μE m−2 s–1, maximum net photosynthetic rate of greenhouse-grown plants was 35 mg CO2 dm−2 h–1 and maximum transpiration rate was 6.7 μg H2O cm−2 s–1. Dark respiration rate was 1.4 mg CO2 dm−2 h–1 and the light compensation point was 17.5 μE m−2 s–1. Carbon dioxide compensation point increased from 25 ppm at 15 C to 43 ppm at 30 C. At saturating photosynthetic photon flux densities, optimum leaf temperature for net photosynthesis was about 25 C. Maximum net photosynthesis of leaves of field-grown plants averaged 15.8 mg CO2 dm−2 h–1. After a 24-h exposure to 0.075 kg ha–1 metribuzin, maximum net photosynthesis and transpiration were reduced 85 and 40%, respectively. Soil water deficits reduced maximum net photosynthesis about 50%.

Laboratory studies demonstrated that naptalam safens cucumber against the phytotoxic effects of chloramben. In petri dish studies, cucumber seedlings grown from seeds exposed to chloramben plus naptalam had greater shoot growth, root growth, and dry weight than seedlings grown from seeds exposed to chloramben alone. Naptalam also partially reversed the reduction in dry weight of various plant parts caused by exposure of roots of hydroponically grown seedlings to chloramben. More radioactivity from root-applied 14C-chloramben remained in cucumber roots and less was translocated to shoots with a 14C-chloramben plus naptalam treatment than with a 14C-chloramben alone treatment. Naptalam appeared to influence chloramben metabolism. In various plant parts, concentrations of chloramben and its metabolites differed between the two treatments.

Optimum temperature for germination and emergence of redvine seed in either petri dishes or soil was 35 C. Reductions in germination and emergence occurred at constant temperatures above or below this temperature. No germination or emergence occurred at temperatures above 40 or below 25 C. Germination in petri dishes first occurred on day 8, and emergence was first observed 12 days after planting in a soil medium. Maximum redvine seedling emergence of 74% occurred in soil when seed were planted 0.5 cm deep, with decreases in emergence noted at depths below 5 cm. No emergence occurred over the 35-day period evalμated when redvine seed were planted on the soil surface or at a depth of 10 cm in soil. Redvine germination was not affected by solution pH, whereas germination did not occur when osmotic stress of as little as −200 kPa was applied to seed.

Virginia buttonweed seeds germinated at temperatures between 15 and 40 C, with optimal germination occurring at 25 or 30 C in 12 h light alternated with 15 to 25 or 20 to 30 C in darkness, respectively. Germination rate was lower in continuous darkness than in light. Germination was reduced under simulated water stress conditions with less than 10% of seeds germinating at osmotic potentials below −0.3 MPa. Overall seed germination was reduced under simulated flooding conditions; greater germination occurred in aerated water than in unaerated water. Maximum germination occurred at pH 6. Seedlings emerged from depths as great as 8 cm, with maximum emergence occurring from 2 cm.

Four years of field experiments were used to assess the competitive ability of red rice, a weedy variety of rice, and ‘Mars’, a cultivar of rice. Red rice was the dominant competitor each of the 4 yr, and an average of one red rice plant reduced Mars grain yield per plant equal to the effect of four Mars plants. Intervarietal competition was more important than intravarietal competition for Mars, whereas the reverse was true for red rice. The product of the coefficients for intravarietal competition did not significantly exceed the product of the coefficients for intervarietal competition, indicating that the two varieties were competing for the same resources. Using the reciprocal yield model coefficients from 1989, grain yield losses of Mars, due to red rice densities of 4, 16, 25, and 300 plants m−2, were predicted to approximate 13, 37, 48, and 92%, respectively, at a fixed cultivar density of 100 plants m−2.

Field studies were conducted to determine the effect of varying densities of hairy nightshade and varying durations of interference on the biomass and seed yield of dry beans. As few as two hairy nightshade plants per meter of row reduced bean seed yield by an average of 13% over the 2 yr of the study. Increasing the density of hairy nightshade to 100 plants per meter resulted in bean yield losses of 77%. Hairy nightshade interference during the first 3 weeks after crop emergence was sufficient to reduce bean yields. Up to 9 weeks of hairy nightshade-free maintenance after crop emergence was required to prevent bean yield losses. Hairy nightshade was a prolific seed producer. At low infestation densities, over 45 000 seeds per plant were produced. Hairy nightshade seed production peaked at over 300 000 seeds m–1 at about 30 plants per m of row. Depending on the length of the growing season, 6 to 9 weeks of weed-free conditions after crop emergence were required to prevent hairy nightshade from producing viable seeds before the first killing frost in the fall. Results are discussed in terms of timing and longevity of control required to reduce hairy nightshade interference in dry beans.

Experiments were conducted to evaluate the effects of preemergence herbicides on the growth characteristics and competitiveness of sicklepod and common cocklebur to soybean. Alachlor was applied at 1.1 or 2.2 kg ai ha–1 and metribuzin at 0.2 or 0.4 kg ai ha–1 in glasshouse and field experiments. Alachlor at 2.2 kg ha–1 reduced sicklepod dry weight and leaf area 4 weeks after planting. Sicklepod water use was initially lowered by both rates of alachlor while soybean and common cocklebur water use was initially lowered by metribuzin at 0.4 kg ha–1. Sicklepod and common cocklebur fresh weights were reduced at soybean harvest by the high rates of alachlor and metribuzin. Soybean competing with sicklepod injured by 1.1 or 2.2 kg ha–1 of alachlor produced yields greater than soybean competing with untreated sicklepod. Soybean yields were not improved when metribuzin was used on common cocklebur.

Greenhouse and field experiments were conducted to determine the effectiveness of dichlormid, R-29148, CGA-92194, flurazole, naphthalic anhydride, and MON-5500 as herbicide antidotes for triallate in wheat and to determine triallate antagonism by seed-applied fungicides and insecticides. Seed treatment of MON-5500 at 0.063% wt/wt was the most effective antidote for triallate in wheat in both greenhouse and field. Dichlormid and R-29148 at 0.5% wt/wt were more effective as antidotes for triallate in wheat than either CGA-92194 or naphthalic anhydride. Flurazole, as a seed treatment, did not reduce triallate injury to wheat Dichlormid or R-29148 at 2.2 kg ai ha–1 applied broadcast to soil and incorporated reduced injury to wheat from triallate at 1.1 kg ai ha–1 and also reduced injury to oats from 0.3 kg ha–1 triallate. Seed treatments of carboxin at 0.2% wt/wt or imazalil at 0.008% wt/wt antagonized triallate and decreased injury to wheat from triallate at 0.6 kg ha–1. Maneb plus lindane or mancozeb treatment of wheat seed increased injury from triallate.

Four field locations were used to compare environmental factors on efficacy of four postemergence grass herbicides in Kentucky bluegrass and bermudagrass turf. Imazaquin, BAS 514, and tridiphane were compared to fenoxaprop-ethyl, a registered herbicide, for postemergence control of large crabgrass. Best large crabgrass control was provided by BAS 514 and fenoxaprop-ethyl. Use of BAS 514 gave equal turf quality, phytotoxicity to the turf, large crabgrass control, and stand compared to fenoxaprop-ethyl. Imazaquin and tridiphane reduced turf quality and were phytotoxic to both turf types, and did not control large crabgrass adequately.

Cultivation timings were used in conjunction with postemergence herbicides to determine their effect on sicklepod control in soybean. Treatments using cultivation alone resulted in less than 70% sicklepod control. A postemergence application of chlorimuron following metribuzin applied postemergence was usually more effective in controlling sicklepod with cultivation 7 days after application than with cultivation 3 days before or at application, or with no cultivation. Cultivation at any timing in conjunction with a postemergence application of imazaquin following imazaquin preemergence improved sicklepod control compared to imazaquin without cultivation. Sicklepod control with chlorimuron postemergence followed by cultivation 7 days after application was as good as or better than two sequential applications of chlorimuron with no cultivation. Imazaquin or metribuzin preemergence followed only by cultivation provided less than 80% control in two of three experiments.

Field studies were conducted in Louisiana to determine growth and yield effects resulting from the accidental application of the isopropylamine formulation of glyphosate to sugarcane. Glyphosate at 0.1, 0.2, 0.4, and 0.8 kg ae ha–1 was applied in water at 90 L ha–1 in May, June, and August. Sugar yields (kg ha–1) were reduced 44% when glyphosate was applied over the top of sugarcane at 0.2 kg ha–1 in June; similar reductions for the May and August applications required 0.4 kg ha–1. Reductions in sugar yield were primarily attributed to reductions in both cane yield and recoverable sugar in the crushed juice because stalk populations and stalk weights were lowered and immature stalks that survived contained less sugar. The recoverability of the subsequent ratoon crop was also affected, particularly when glyphosate was applied in May and June to the previous crop at rates of 0.4 kg ha–1 and higher.

Greenhouse and field studies were conducted to determine the influence of herbicide rate, hybrid variability, and soil moisture on the effectiveness of CGA-154281 in protecting corn seedlings from metolachlor injury. High rates of metolachlor caused significant injury to seedlings of sensitive corn hybrids. However, with metolachlor plus CGA-154281, very few injury symptoms were observed, even with the 7.8 kg ha–1 rate and the most sensitive hybrid. Corn seedlings were not injured by metolachlor plus CGA-154281 at the highest soil moisture level evaluated, whereas those treated with metolachlor alone showed 70% injury. Metolachlor injury increased as soil moisture content increased. In the greenhouse, CGA-154281 did not protect any of the eight weed species tested against injury by 2.2 kg ha–1 metolachlor. In laboratory studies, CGA-154281 did not alter the absorption of 14C-metolachlor during an 8-h period. Qualitative comparison of the metabolism of metolachlor in the presence or absence of the protectant indicated that metolachlor was metabolized to a more polar metabolite, believed to be a glutathione conjugate. However, CGA-154281 significantly enhanced the rate of metabolism of metolachlor in three of the four hybrids tested. Metolachlor metabolism activity may already have been functioning at a maximum level in the unaffected hybrid.

High herbicide costs and uncertainty about annual weed control at planting have limited adoption of no-till spring wheat production systems in the northern Great Plains. Chlorsulfuron, metsulfuron, and CGA-131036 at 10 to 20 g ai ha–1 plus nonionic surfactant generally controlled both emerged kochia and wild mustard equally well (>80%) whether or not combined with glyphosate at 250 g ha–1 plus nonionic surfactant. In two of three trials persistent phytotoxic residues of these sulfonylurea herbicides in soil controlled both weeds better in midseason and early summer 1 yr after treatment than did glyphosate, which has only foliar activity. While the absolute net returns of different treatments varied among herbicides, relative net returns were insensitive to changes in either herbicide or wheat price. Herbicide use tended to boost net returns for no-till spring wheat in years with good weather but depressed net returns in a drought year. Chlorsulfuron at 10 and 20 g ha–1 increased net returns in all three trials. Metsulfuron and combinations of either metsulfuron or chlorsulfuron with glyphosate had variable effects on net returns.

Weed seedlings were grown in a composite soil contained within a semipermeable membrane that allowed the development of consistent, reproducible levels of plant water stress. The water content of membrane units with a 1-cm cross section equilibrated most rapidly, within 3 to 5 days, with the external osmotic solution. The water potential (Ψ) of green foxtail grown in plant growth membrane units was curvilinearly related to the external polyethylene glycol (PEG) osmotic solution Ψ. This relationship permitted nondestructive estimation of plant Ψ. Green foxtail shoot growth in membrane units was reduced by decreasing Ψ of the external PEG osmotic solution and was completely arrested by high water stress induced by an −800 kPa external osmotic solution. The technique makes possible precise control and relatively rapid adjustment in the level and duration of plant Ψ of seedlings and small plants.

Pendimethalin dissipation was studied following annual 1.7 kg ai ha–1 applications to 3-yr-old Kentucky bluegrass turf growing on a Sharpsburg silty clay loam soil and an 85/15 by volume sand/Sharpsburg soil mixture in 150-cm-deep rhizotron containers. Plant tissue, thatch, and soil were sampled periodically between application and 168 days after treatment (DAT). Soil and leachate were collected to monitor pendimethalin movement. Most of the herbicide appeared to remain within the turfgrass system. Pendimethalin concentration was highest in plant tissue and thatch. The 4-hydroxymethyl pendimethalin metabolite was detected in turfgrass tissue up to 42 DAT. No pendimethalin was detected at the 30-, 60-, or 120-cm depths in the rhizotron containers. Traces (≤0.003 mg kg–1) of pendimethalin detected in rhizotron leachate collected between 6 and 14 days after heavy rainfall (88 and 95 DAT, respectively) were attributed to gravitational displacement of soil colloids containing adsorbed herbicide. Pendimethalin application to established turfgrass would not appear to pose a high risk of groundwater contamination.

Studies were conducted to determine the effect of ensiling and/or rumen digestion by cattle on the germination and viability of several common weed species. Seed survival of grass species subjected to ensiling and/or rumen digestion tended to be less than that of broadleaf species. Downy brome, foxtail barley, and barnyardgrass were nonviable after either ensiling for 8 weeks or rumen digestion for 24 h. Some green foxtail (17%) and wild oats (0 to 88%) seeds survived digestion in the rumen but were killed by the ensiling process. Varying percentages of seeds of kochia, redroot pigweed, common lambsquarters, wild buckwheat, round-leaved mallow, and field pennycress remained viable after ensiling (3 to 30%), rumen digestion (15 to 98%), and ensiling plus rumen digestion (2 to 19%). A time course study of rumen digestion indicated that loss of seed viability often was not a gradual process. With some species, there was an initial lag phase while degradation of the protective seed coat likely occurred, followed by a rapid decline in embryo viability. The diet fed to livestock appeared to affect viability losses caused by rumen digestion. Estimates of seed survival with varying rates of passage through the rumen due to differing ratios of grain to forage in the diet are presented.

Sixty isolates of the plant pathogenic fungus Sclerotinia sclerotiorum (Lib.) de Bary and six isolates of Sclerotinia minor Jagger were evaluated in a controlled environment for virulence on leaves excised from 8-week-old dandelion plants. Significant negative correlations were obtained between the relative virulence of the isolates and the dry weights of dandelion plants inoculated in a controlled environment; and positive correlations were detected between the relative virulence of isolates and reduction in number of dandelion plants in turfgrass swards infested with inoculum of the isolates. In August 1988, an 80.7% reduction in the number of dandelion plants was detected in a turfgrass sward treated in 1987 with four applications of heat-killed seed of perennial ryegrass (100 g m−2 application–1) infested with isolate R30 of S. sclerotiorum, followed by six applications at the same rate in 1988. Populations of dandelions in untreated swards increased by 22.2% during the same period. Heat-killed seed of perennial ryegrass (100 g m−2) infested with isolate R30 applied simultaneously with dandelion seed (25 g m−2) onto a sward of Kentucky bluegrass reduced the establishment of dandelion seedlings by 85.5%. Necrosis or discoloration did not develop on Kentucky bluegrass, creeping bentgrass, annual bluegrass, or quackgrass treated with inoculum of Sclerotinia. Sclerotia of Sclerotinia spp. were found, on occasion, in crowns but not on the foliage of diseased dandelions.