Florpyrauxifen-benzyl is a new active ingredient that represents an additional tool in rice (Oryza sativa L.) weed control by providing an alternative mechanism of action. Studies were conducted to evaluate soil moisture influences on florpyrauxifen-benzyl absorption, translocation, and metabolism in three problematic weeds. In the absorption/translocation study, barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.], hemp sesbania [Sesbania herbacea (Mill.) McVaugh], and yellow nutsedge (Cyperus esculentus L.) were treated with [14C]florpyrauxifen-benzyl under two soil moisture regimes (7.5% and 60% field capacity). Greater absorption occurred under moist conditions (60% soil moisture content). More translocation of the herbicide to the area above the treated leaf occurred under moist versus dry soil across all weed species. Sesbania herbacea translocated 25% of the absorbed herbicide above the treated leaf, a result greater than that of the other two weed species at 60% soil moisture. However, no differences in translocation occurred among the weed species at the 7.5% soil moisture regime. In the metabolism study, 95% of the herbicide recovered was in its acid form under the high soil moisture regime for S. herbacea, a species that shows extreme sensitivity to even low doses of this herbicide, and soil moisture influenced the amount of acid form found in all species. While these data provide a limited view into the physiological processes being affected, they do suggest that for E. crus-galli, S. herbacea, and C. esculentus, soil moisture content in the field will likely play a significant role in absorption, translocation, and metabolism of florpyrauxifen-benzyl.

Purple moonflower's (Ipomoea turbinata Lagasca y Segura) vegetative growth and seed maturation were characterized in noncompetitive field studies. Seedling emergence of 50% or greater of mature scarified seed occurred to a soil depth of 12 cm. At vegetative maturity a typical plant produced 11 primary, 50 secondary, 94 tertiary, and 7 quaternary runners having a total length of 185 m. The average number of leaves per plant was 1,120. Maximum seed size, seed wet weight, occurrence of first mottled seed, and first capacity to germinate occurred 20 days after anthesis in immature seed that were removed from the seed pod. Maximum germination occurred at 26 days after anthesis. Seed moisture content (dry weight basis) reached 8.5%, seed had formed an impermeable seed coat, and physiological maturity (defined as maximum dry weight) occurred 34 days after anthesis. The total number of purple moonflower seed produced per plant averaged 9350. The major mechanism of seed dormancy was impermeability of seed coats.

The need for reducing costs and making grape production more sustainable has prompted the search for alternative weed control practices that optimize production while maintaining profits. For this reason, it is imperative to understand how different weed management practices modify vine–weed interactions. In the present study, we evaluated the effect on weed growth and Zinfandel grapevine growth and production of five weed control practices: (1) flumioxazin, (2) simazine, (3) cultivation, (4) cover crop, and (5) untreated control. The herbicide treatments had the lowest weed biomass, followed by the cultivation, being approximately 10 and 2 times lower than the weed biomass of either the cover crop or untreated control treatments, respectively. However, the differences in grape yield were not as evident. In 2006, a rainy year, the herbicides and cultivation treatments did not differ in grape yield, but the cover crop and untreated control had a reduction of approximately 20% compared with the other treatments. In 2007, a dry year, in comparison to the herbicide treatments, the grape yield reductions of cultivation were around 22%, and those of the cover crop and untreated control were around 48%. Although the cover crop reduced grape yield, it suppressed weed species considered important, such as horseweed, panicle willowherb, scarlet pimpernel, and sowthistle. Also, it was concluded that vines can tolerate a certain amount of weed competition, and that properly timed postemergence control actions (e.g., cultivation or POST herbicides) could provide the necessary level of control to obtain the desired yields. However, under limited soil moisture conditions, the use of PRE herbicides could prove important to maintain vine yield and vigor.

When crop plants were competing with well-established quackgrass (Agropyron repens) for the same nutrient supply, chlorosis and stunting of crop plants occurred. Apparently this was due to the greater ability of quackgrass to withdraw available nutrients, especially nitrogen, and to a lesser extent phosphorus and potassium, from the nutrient solution. No evidence was obtained for a phytotoxic substance from living quackgrass roots or rhizomes that could inhibit germination or growth of alfalfa and oats. Quackgrass residues in large amounts caused chlorosis and stunting in alfalfa and oats when added to soil. The evidence obtained linked this behavior to the high C:N ratio with consequent temporary deficiency of available nitrogen. Water extracts of quackgrass leaves or rhizomes were not phytotoxic unless subjected to high temperatures during or subsequent to extraction. If soils contained decomposing quackgrass or crop plant residues, extremely phytotoxic extracts of such soils were obtained, but only when soils were saturated and decomposition was anaerobic.

Field and greenhouse experiments were conducted in 1995 and 1996 to determine soybean injury and weed control differences from imazamox and imazethapyr applied postemergence with a nonionic surfactant or methylated seed oil and with selected tank mixtures. Soybean injury from imazamox at 35 g ai ha−1 plus either a methylated seed oil or nonionic surfactant was equal to injury from imazethapyr at 70 g ai ha−1 in the greenhouse and field. Imazamox provided greater common lambsquarters control than imazethapyr in the field in 1995 and in the greenhouse. Thifensulfuron tank mixed with imazethapyr increased common lambsquarters control, while soybean response increased when thifensulfuron was tank mixed with imazamox. Common ragweed dry weight was reduced 61 to 64% from 35 g ha−1 imazamox and 70 g ha−1 imazethapyr in the field; however, imazamox provided greater common ragweed control than imazethapyr in the greenhouse. Tank mixtures of lactofen with imazamox or imazethapyr increased common ragweed control and resulted in greater soybean seed yield in 1996 than when imazamox and imazethapyr were applied alone; however, lactofen antagonized giant foxtail control with imazamox and imazethapyr, and antagonized common lambsquarters control with imazamox. Giant foxtail control in the greenhouse was antagonized more when acifluorfen, fomesafen, and lactofen were tank mixed with 35 g ha−1 imazethapyr than with 35 g ha−1 imazamox. Giant foxtail control with imazamox or imazethapyr applied alone or with diphenyl ether herbicides increased when 28% urea ammonium nitrate was added with nonionic surfactant compared with nonionic surfactant only. Imazethapyr antagonized giant foxtail control by clethodim in the field and was more antagonistic than imazamox in the greenhouse. A methylated seed oil improved common ragweed control by imazethapyr at 70 g ha−1 and imazamox at 18 and 35 g ha−1, while common lambsquarters and velvetleaf control increased when a methylated seed oil was included with 18 g ha−1 imazethapyr compared to nonionic surfactant in the greenhouse.

Rhizome johnsongrass [Sorghum halepense (L.) Pers.] in late-planted soybeans [Glycine max (L.) Merr. ‘Forrest’] was effectively controlled with glyphosate [N-(phosphonomethyl)glycine] applied twice by a rope-wick applicator at 0.1 kg/ha each time. At crop maturity, wick-applied glyphosate controlled an average of 92% of the johnsongrass over a 2-yr period as compared to 51% where 2.2 kg/ha of glyphosate was applied conventionally to rhizome johnsongrass prior to planting. There was no difference in soybean yields and no visible injury to soybeans. Rhizome johnsongrass and volunteer corn (Zea mays L.) were effectively controlled in soybeans planted at the proper time with glyphosate applied by either the rope-wick applicator or recirculating sprayer. Soybean yields were reduced more when volunteer corn was treated with glyphosate that was applied with a recirculating sprayer than with a rope-wick applicator. This reduction in yield was attributed to splattering of the herbicide.

The foliage and roots of Canada thistle (Cirsium arvense (L.) Scop.) readily absorbed 2-methoxy-3,6-dichlorobenzoic acid (dicamba) after which it was translocated by both phloem and xylem. The results are in harmony with a source-to-sink system of dicamba translocation in the phloem. Following foliar application, small amounts of dicamba were exuded by the roots into surrounding soil. Dicamba tended to accumulate in young, growing leaves following both foliar or root uptake. Leaves, but not roots, retained a substantial portion of the dicamba taken up. After 54 days, 63.1% of the recovered radioactivity in the treated leaf was still in the form of unaltered dicamba. The remaining 36.9% was in the form of an unidentified product. In other plant parts, much less change occurred. During a 54-day period, one-fifth of the dicamba applied was recovered as radioactive CO2.

Cucumber (Cucumus sativus L. ‘Chicago pickling’) and wheat (Triticum aestivum L. ‘Manitou’) seeds were germinated in various concentrations of (2,4-dichlorophenoxy) acetic acid (2,4-D), (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), 3,6-dichloro-o-anisic acid (dicamba), and 4-amino-3,5,6-trichloropicolinic acid (picloram). The nucleic acid and protein levels in the roots of the two species were determined 4 days after germination and compared on a per root basis. All four herbicides increased the DNA and protein of both cucumber and wheat roots with the increase in cucumber being higher than in wheat. The greatest difference between the tolerant wheat and susceptible cucumber was the effect on the RNA levels. As the concentration of all four herbicides increased, a progressive decrease of RNA levels occurred in wheat. In contrast, in cucumber the herbicides at high concentrations (10 and 100 ppmw) increased the RNA levels by more than 200% over the water controls. When the protein levels in both species were compared on a per unit RNA basis, there was an inverse relationship. In wheat the protein/RNA ratio was higher than the control whereas in cucumber the ratio was lower. A differential alteration of RNA species and interference with protein synthesis is suggested as the basis for selectivity.

Applications of glyphosate [N-(phosphonomethyl)glycine] to the leaves of pea (Pisum sativum L. ‘Burpee's Blue Bantam’), sunflower (Helianthus annuus L. ‘Mammoth’), and bean (Phaseolus vulgaris L. ‘Red Kidney’) reduced transpiration in all three species. The reduction varied with species and concentration applied. Eight-day-old bean leaves responded earlier than leaves on older plants. However, after 29 h, there was no difference in transpiration rates with seedling age, since treated leaves on both ages investigated were transpiring at about one-half the rate of control leaves. Addition of surfactant to the solution shortened the time interval between treatment and transpirational response but did not affect the final transpiration rate as compared to glyphosate without surfactant. The effect of glyphosate on transpiration was not due to changes in water availability or to the surface of the leaf that was treated. It is suggested that these results can give some insight into uptake, translocation, and mode of action of glyphosate.

Much of the success of modern agriculture is due to pesticide technology. Because weeds pose the greatest threat to crop yields, the largest class of pesticides used today is herbicides. Herbicides include products whose active ingredients represent a wide range of chemical families; yet most constitute a minimal potential hazard to man and the environment. Criteria typically used to determine potential hazard are mammalian and piscine toxicity, persistence, and bioaccumulation. By evaluating these criteria and assigning numerical values it is possible to devise a ranking of pesticides such as that developed by Weber (51). This list identifies those pesticides most likely to have some undesirable activity, either before or after they are applied. All herbicides ranked well below organochlorine insecticides in hazard rating and most were less hazardous than the organophosphate and carbamate insecticides. However, any substance, when used improperly, has the potential to cause problems, and for this reason all chemicals should be handled with caution.

A shattercane biotype resistant to primisulfuron was identified during greenhouse evaluations of seed obtained from southeastern and south-central Nebraska fields previously treated with primisulfuron or nicosulfuron a minimum of 3 consecutive yr. Absorption, translocation, metabolism, and acetolactate synthase (ALS) assay experiments were conducted to determine resistance mechanism(s) by comparing ALS-susceptible forage sorghum (ROX) to resistant shattercane (RS). The ROX had 10 and 12% greater 14C absorption than RS 24 and 96 hours after treatment (HAT), respectively. Absorption of 14C increased over time for both ROX and RS, while 14C translocation from the treated leaf to the shoots and roots was similar for ROX and RS. Unmetabolized primisulfuron accounted for > 80% of the radioactivity recovered 24 h after application for both ROX and RS. The ROX and RS had similar ALS-specific activities and total protein concentrations. K m values for RS and ROX were 10.4 and 5.8 mM pyruvate, respectively. The ALS isolated from RS was less sensitive than ROX to inhibition by primisulfuron. The I50 values for RS and ROX were 231 and 0.025 μM primisulfuron, respectively. The mechanism of primisulfuron resistance in this RS biotype is an altered ALS with decreased sensitivity to primisulfuron.

Italian ryegrass interference in broccoli was measured in field experiments and the data fit a rectangular hyperbolic competition model. The model predicted 58% of broccoli yield loss related to Italian ryegrass density when pooled over three y. An economic threshold value of 4.9 Italian ryegrass plants m−1 of crop row was determined to be the density required to cause a 3.6% yield loss, equal to postemergence weed control costs. Italian ryegrass densities of 600 to 1000 plants m1 of broccoli row caused 100% yield loss.

The effects of ethylene upon germination of common cocklebur (Xanthium pensylvanicum Wallr.) and redroot pigweed (Amaranthus retroflexus L.) seeds were studied. In laboratory tests with seeds in sealed flasks in the dark, 10 μl/L ethylene increased germination of redroot pigweed seeds from 7% to 52% at 30 C, and increased germination of large and small common cocklebur seeds from 30% and 0% to 100% and 90% respectively, at 25 C. At least 12 h of exposure to ethylene was necessary for appreciable stimulation of germination. In growth chamber studies with known numbers of seeds in pots of soil, ethylene at 11 kg/ha was injected into the soil, and the pots were enclosed in plastic bags for 24 h. One such injection at 2 weeks after planting, and successive injections at 2, 3, and 4 weeks, significantly increased redroot pigweed seedling emergence, and significantly decreased the numbers of dormant, viable seeds remaining in the soil. When pots were not enclosed, injections did not significantly effect redroot pigweed seeds, but significantly increased common cocklebur seedling emergence and decreased the number of viable common cocklebur seeds remaining in the soil.

Univariate analyses fail to account for covariance among phenomorphological traits implicated in crop competitive ability. A more complete analysis of cultivar–weed interactions would reduce a number of important traits to a few underlying principal factors responsible for sweet corn competitiveness. Twenty-three commercial sweet corn hybrids from nine seed companies were grown in the presence and absence of wild-proso millet to (1) quantify the extent to which phenomorphological traits vary in sweet corn, (2) identify underlying principal factors that describe variation in crop canopy development, and (3) determine functional relationships between crop canopy factors and competitive ability. A principal component factor analysis revealed that 7 of the 18 weed-free crop traits measured at silking loaded highly (0.65 to 0.90) into the first factor, including plant height, shoot biomass, per plant leaf area, leaf area index, and intercepted light, as well as thermal time from emergence to silking and emergence to maturity. All seven traits were highly correlated (0.38 to 0.93) and were interpreted as a “late canopy and maturity” factor. Another five traits formed two additional principal factors that were interpreted as an early “seedling quality” factor (e.g., kernel mass, seedling vigor, and height at two-leaf stage) and a mid-season “canopy closure” factor (e.g., leaf area index and intercepted photosynthetically active radiation at six-leaf stage). Relationships between principal factors and competitive abilities were quantified using least-squares linear regression. Cultivars with greater loadings in the late canopy and maturity and canopy closure factors were more competitive with wild-proso millet. In contrast, crop competitive ability declined with cultivars that loaded highly into the seedling quality factor. The analyses showed that sweet corn's ability to endure weed interference and suppress weed fitness relates uniquely to three underlying principal factors that capture crop canopy development around emergence and near canopy closure and during the reproductive phase.

Established stands of alfalfa (Medicago sativa L. ‘Lahontan’) at six field locations were treated with soil-active herbicides during the dormant period for the control of winter annual weeds. Weeds and alfalfa were hand separated at the first harvest. This forage, which varied widely in weed content, was analyzed for protein. The percentage of protein correlated negatively with weed content in all cases. Analyses of covariance revealed that the direct effect of the herbicides on protein content was either small or absent and that the primary cause of the negative correlations was weed content.

Considerable attention has been given during recent years to the fate of herbicides sprayed onto soil surfaces. The effect of light upon herbicides also has been studied extensively. Payne and Fults by means of a biological test found that the potency of 2,4–D was increased by exposure to ultraviolet light. Hansen and Buchholtz found that when a solution containing 2,4–D and riboflavin was exposed to light the activity of 2,4–D was reduced. They tentatively identified the breakdown product as 2,4–dichlorophenol. Later Bell positively identified it.

The practical use of ethyl N,N–di–n–propylthiolcarbamate [EPTC] has been studied intensively by weed research workers since introduction of the herbicide in 1957. Early studies were devoted to its evaluation as a soil-surface application for control of germinating weed seed. Studies conducted in 1958 showed that the activity of EPTC could be greatly increased by soil-incorporation immediately after application and emphasis shifted to soil-incorporation research. In general, the accumulated applied research data on the use of EPTC in pre-planting, or lay-by, soil-incorporated treatments have emphasized the pressing need for basic investigations on the effects of soil composition and reaction, temperature, light, moisture, method and depth of incorporation, and method of formulation on the activity of this herbicide. A limited number of basic studies have been conducted on the effects of soil composition and moisture on the performance and persistence of EPTC. However, basic research must be intensified if the excellent herbicidal potentialities of EPTC and other soil-active carbamates are to be utilized to their fullest extent.

Field experiments were conducted in 1982 and 1983 at Stoneville, MS, to determine the susceptibility of 17 biotypes of bermudagrass [Cynodon dactylon (L.) Pers. ♯ CYNDA] to seven postemergence herbicides. Control, averaged over all biotypes 13 weeks after treatment, varied from 96% using haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} at 0.56 kg/ha to 16% using fenoxaprop {(±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy]propanoic acid} at 0.28 kg/ha. Control among biotypes ranged from 89 to 96% using haloxyfop at 0.56 kg/ha and from 4 to 89% using dalapon (2,2-dichloropropanoic acid) at 11.2 kg/ha.

American sloughgrass is a troublesome grass weed in winter wheat fields after rice in China. Mesosulfuron-methyl failed to control American sloughgrass in Danyang County in 2012. The purpose of this research was to determine the resistance level to mesosulfuron and other herbicides in American sloughgrass and to identify the molecular basis of resistance. Dose–response experiments indicated that this population was moderately resistant to mesosulfuron-methyl (7.6-fold) and pyroxsulam (6.0-fold), highly resistant to flucarbazone-sodium (20.3-fold), fenoxaprop-p-ethyl (565.0-fold), clodinafop-proargyl (19.5-fold), and pinoxaden (45.9-fold), and susceptible to isoproturon. Part of the acetolactate sythase (ALS) gene was cloned and sequenced to confirm the molecular mechanism of resistance to ALS-inhibiting herbicides. A Pro197Ser substitution was identified. This substitution is likely the molecular mechanism of resistance to mesosulfuron-methyl in the Danyang population in which it is cross-resistant to flucarbazone-sodium and pyroxsulam. This study established the first report of mesosulfuron-methyl resistance likely caused by a Pro197 substitution in American sloughgrass and a potential herbicide to control this resistant weed.

Movement of 2-methoxy-3,6-dichlorobenzoic acid (dicamba) and N,N-dimethyl-2,2-diphenylacetamide (diphenamid) in Hagerstown silty clay was greater with either 5 or 10 surface inches of water when the water was applied in 0.25-inch increments rather than 1-inch. Upward movement of these herbicides occurred under sub-irrigation and when surface-applied water was allowed to evaporate freely from the soil surface. Dicamba always moved more readily than diphenamid. The results indicate that weather patterns may be important in addition to total rainfall in determining the movement of herbicides in soil.