Field experiments were conducted to evaluate pyridine herbicides for Virginia buttonweed control and turfgrass tolerance. Treatments included clopyralid and fluroxypyr applied at 35, 70, 140, 280, and 560 g ae/ha, compared to a three-way combination of 2,4-D plus dichlorprop plus dicamba (840 + 840 + 210 g ae/ha, respectively). Fluroxypyr applied at 140 g/ha or greater controlled Virginia buttonweed 80% or greater through 10 wk after treatment. A second experiment evaluated 280 g/ha clopyralid or 140 g/ha fluroxypyr alone or in combination with 0.25 or 0.50% (v/v) nonionic surfactant, compared to 280 g/ha dicamba or 1,120 g/ha 2,4-D alone or in combination with nonionic surfactant. The addition of nonionic surfactant to clopyralid or fluroxypyr did not increase Virginia buttonweed control. Fluroxypyr at 280 g/ha and higher produced 22 to 53% injury to bermudagrasses 2 wk after treatment. Common centipedegrass was injured through 3 wk after treatment with 4,470 g/ha fluroxypyr or greater. Zoysiagrass exhibited injury with 4,470 g/ha fluroxypyr at 2 wk after treatment; however, injury was less than 8% at 3 wk. Common St. Augustinegrass was severely injured with 2,235 g/ha or greater fluroxypyr through 7 wk after treatment. Clopyralid did not cause injury to any turfgrass species.

Component yields and forage quality were evaluated in established stands of alfalfa seeded alone and in binary mixtures with smooth bromegrass, orchardgrass, or timothy. Forage yields and quality were determined at three annual harvests in the third and fourth years after seeding. Weed yields in alfalfa seeded alone were significantly greater than those in the alfalfa–orchardgrass mixture. Average weed content was 24, 17, 2, and 15% for the alfalfa seeded alone, alfalfa–bromegrass, alfalfa–orchardgrass, and alfalfa–timothy, respectively. Seeding alfalfa with orchardgrass increased first harvest and annual forage yields while reducing alfalfa yield. Yields of orchardgrass often exceeded those of bromegrass or timothy. In the first harvest each year, crude protein was reduced and acid detergent fiber and neutral detergent fiber increased by including orchardgrass. Neutral detergent fiber was greater in alfalfa–orchardgrass than in the alfalfa seeded alone at most harvests. There were no consistent differences among the alfalfa seeded alone and the other mixtures in yield or quality.

A field study was conducted in 2009, 2010, and 2011 on a grower's field with a known population of glyphosate-resistant giant ragweed to determine potential control options utilizing a WideStrike® cotton variety. Glyphosate-resistant giant ragweed control and cotton response to herbicide applications were both assessed. Few herbicide treatments provided greater than 80% control. Glufosinate followed by glufosinate was the only treatment that provided greater than 90% control at each assessment timing. Other effective treatments were glufosinate alone, glufosinate plus glyphosate, glyphosate plus pyrithiobac, and glufosinate plus fluometuron. Results from this study indicate that few of the studied herbicide treatments provide effective control of glyphosate-resistant giant ragweed without reducing yield in WideStrike cotton. Treatments that had the highest level of giant ragweed control at all ratings and also had the highest yield included glufosinate followed by glufosinate, glufosinate plus pyrithiobac, and glufosinate plus fluometuron at either rate. However, glufosinate followed by glufosinate was the only treatment that resulted in greater than 90% control of giant ragweed without reducing crop yield.

Dinitroaniline and amide herbicides have been continually applied in garlic in China, leading to the change of weed community and dominant weed species. Catchweed bedstraw, shepherd's-purse, and flixweed have become major troublesome weeds. Crop safety of fluorochloridone to 18 crops (at rates of 500 and 1,000 g ai ha−1) and weed efficacy against 35 weeds (at rates of 125 and 250 g ha−1) were determined in greenhouse studies. Visual estimate indicated that fluorochloridone was not safe to many crops, especially cruciferous crops. Among all of the trial crops, garlic was the only crop which was not injured in both PRE and POST application at rate of 500 g ha−1, even when treated with 1,000 g ha−1. Fluorochloridone showed high efficacy against most weeds tested in this experiment when applied PRE, but could not offer a satisfactory control when applied POST. Further rate-response study of fluorochloridone to garlic and six weeds was also investigated. PRE application of fluorochloridone to garlic was safer than POST, and the rates for 10% growth reductions (GR10s) were 1,959 g ha−1 for PRE and 537 g ha−1 for POST. When applied PRE, GR90s of shepherd's-purse and flixweed were 19.2 and 70.3 g ha−1, respectively. Though GR90 of catchweed bedstraw was 541 g ha−1, it could be totally controlled without injuring garlic. On the basis of these results, fluorochloridone has an excellent prospect for weed control in garlic fields.

In an attempt to refine calibration procedures for greenhouse spray chambers, the effects of an herbicide adjuvant, operating pressure, and travel speed on the static and dynamic spray patterns of single flat-fan hydraulic nozzle tips were studied. The volume output in the central 15 cm of the spray pattern (where target plants would ordinarily be positioned) was used as an indicator of the relative dosages received from both a tapered flat-fan tip (8001 VS) and an even-spray tip (8001 EVS). All tested variables significantly altered the spray pattern. Specifically, dynamic spray patterns differed from static patterns, and speed of travel affected the dynamic pattern for both tapered and even flat-fan sprays. Increasing the travel speed from 0.375 to 0.75 m/s reduced spray deposit in the central 15 cm of the spray pattern by up to 19% for water, and by up to 34% for water containing 0.1% v/v nonionic surfactant. Increasing surfactant concentration to 1% decreased the magnitude of the speed effect. Higher pressure sprays tended to reduce the effect of increased travel speeds. These results show that changes in physicochemical properties of the spray solution as well as air turbulence introduced by nozzle movement can affect the pesticide dosage to which a target plant is exposed in a spray chamber. For proper treatment comparison, delivery systems for greenhouse spray experiments should be calibrated with end-use spray liquids, operating pressures, and nozzle travel speeds.

Enlist E3TM soybean cultivars permit over-the-top application of labeled glyphosate, glufosinate, and 2,4-D choline products. Increased Enlist E3TM trait adoption and use of 2,4-D choline postemergence across U.S. soybean production systems raise concerns regarding potential for 2,4-D off-target movement (OTM). A large-scale drift experiment was established near Sun Prairie, WI, and Arlington, WI, in 2019 and 2020, respectively. A 2,4-D-resistant soybean cultivar was planted in the center of the field (∼3 ha), while the surrounding area was planted with a 2,4-D-susceptible cultivar. An application of 785 ae ha−1 2,4-D choline plus 834 g ae ha−1 glyphosate was completed within the center block at R2 and V6 growth stages on August 1, 2019, and July 3, 2020, respectively. Filter papers were placed in-swath and outside of the treated area in one upwind transect and three downwind transects to estimate particle deposition. Low-volume air samplers ran for the 0.5-h to 48-h period following application to estimate 2,4-D air concentration. Injury to 2,4-D-susceptible soybean was assessed 21 d after treatment (0% to 100% injury). The 2,4-D deposition in-swath was 9,966 and 5,727 ng cm−2 in 2019 and 2020, respectively. Three-parameter log-logistic models estimated the distance to 90% reduction in 2,4-D deposition (D90) to be 0.63 m and 0.90 m in 2019 and 2020, respectively. In 2020, the 2,4-D air concentration detected was lower for the upwind (0.395 ng m−3) than the downwind direction (1.34 ng m−3), although both were lower than the amount detected in-swath (4.01 ng m−3). No soybean injury was observed in the downwind or upwind directions. Our results suggest that 2,4-D choline applications following label recommendations pose little risk to 2,4-D-susceptible soybean cultivars; however, further work is needed to understand 2,4-D choline OTM under different environmental conditions and the presence of other susceptible crops.

Common lambsquarters or fat hen (Chenopodium album L. # CHEAL) was classified by Linneaus in 1753. The generic name is from the Greek chen, a goose, and pous or podos, a foot; the leaf shape of plants in this genus are reminiscent of goose feet. The goosefoot family, Chenopodiaceae, includes many vegetables: table beets, sugar beets, spinach, and mangold. The name ‘fat hen’, used for several plants of the Goosefoot family, was first published in English in 1795.

Cryogens are defined as substances that produce low temperatures. In this study, cryogens refer to salts added to snow or ice to cool underlying soil, resulting in reduced weed establishment. In laboratory experiments, bags of ice mixed with cryogens were able to reach temperatures as low as −17 C. In soil-filled pots stored at 4 C, bags of cryogenic salts filled with ice chips reduced the soil temperatures to below 0 C and reduced the establishment of weeds significantly without salinity effects. The cryogen magnesium chloride-6-hydrate (MC) that was effective in pot experiments was tested in an oat field in 2008 and 2009. Plastic bags containing concentrated solutions of MC, perforated at the top, were placed on bare soil just before snowfall. Contact of snow with MC was expected to decrease the surface soil temperature enough to cause freezing injury to seeds in the soil. Although overall effects on weed establishment were small, the cryogenic effect did significantly reduce corn spurry establishment in 2008, and significantly reduced overall weed establishment in both years. These results show that weed management with cryogenic salts is possible in principle, but requires further technical improvements to be practical in the field.

Weed control in tree nut orchards is a year-round challenge for growers that is particularly intense during winter through summer as a result of competition and interference with management and harvest operations. A common weed control program consists of an application of a winter PRE and POST herbicide mixture, followed by a desiccation treatment in early spring and before harvest. Because most spring and summer treatments depend on a limited number of foliar-applied herbicides, summer-germinating species and/or herbicide-resistant biotypes become troublesome. Previous research has established effective PRE herbicide programs targeting winter glyphosate-resistant weeds. However, more recently, growers have reported difficulties in controlling several summer-germinating grass weeds with documented or suspected resistance to the spring and summer POST herbicide programs. In this context, research was conducted to evaluate a sequential PRE approach to control winter- and summer-germinating orchard weeds. Eight field experiments were conducted in tree nut orchards to evaluate the efficacy of common winter herbicide programs and a sequential herbicide program for control of a key summer grass weed species. In the sequential-application strategy, three foundational herbicide programs applied in the winter were either mixed with pendimethalin, followed with pendimethalin in March, or applied as a split application of pendimethalin in both winter and spring. Results indicate that the addition of pendimethalin enhanced summer grass weed control throughout the crop growing season by up to 31%. Applying all or part of the pendimethalin in the spring improved control of the summer grass weed junglerice by up to 49%. The lower rate of pendimethalin applied in the spring performed as well as the high rate in the winter, suggesting opportunities for reducing herbicide inputs. Tailoring sequential herbicide programs to address specific weed challenges can be a viable strategy for improving orchard weed control without increasing herbicide use in some situations.

Differences in clomazone tolerance among sweetpotato cultivars were first observed in April 2007 after use of the herbicide for weed control in fields containing the sweetpotato breeding project at the U.S. Vegetable Laboratory. Susceptible cultivars and experimental clones exhibited severe foliar chlorosis and reduced growth, whereas the most tolerant were not injured. Twelve cultivars and experimental clones were included in a greenhouse experiment to quantify the differences in clomazone tolerance. In the greenhouse, the clomazone concentration that caused moderate injury or reduction in shoot growth to the most tolerant clones was approximately 10 times the concentration that caused a similar response in the most susceptible clones. Two older cultivars, Excel and Sumor, that were developed before the registration of clomazone for use in sweetpotato were susceptible. Clomazone is an important component in sweetpotato weed management, and susceptibility is an undesirable trait that should be avoided in new sweetpotato cultivars.

Field studies at three sites in Georgia evaluated broadleaf weed and nutsedge management in peanut with PPI applications of imazethapyr and metolachlor and POST applications of paraquat in mixture with imazethapyr or bentazon. Imazethapyr at 36 g ai/ha applied PPI alone or in mixture with metolachlor at 2750 g ai/ha controlled coffee senna; entireleaf, ivyleaf, pitted, smallflower, and tall morningglories; bristly starbur; and prickly sida better than metolachlor applied PPI. Yellow nutsedge control was generally higher where metolachlor was applied PPI. Postemergence control of the aforementioned species and sicklepod was similar with paraquat plus imazethapyr and paraquat plus bentazon. Peanut yields with paraquat plus imazethapyr and paraquat plus bentazon were similar. With one exception, peanut yields from imazethapyr PPI systems were higher than metolachlor PPI systems when POST herbicides were not used. Inclusion of metolachlor with PPI application of imazethapyr increased yields only at one location.

Three experiments evaluated sicklepod interference with soybean with and without preplant incorporated applications of chlorimuron plus metribuzin or imazaquin. Sicklepod density, weed-free period, and weedy period were examined. In the absence of herbicides, soybean seed yield was reduced with 2 sicklepod plants row m-1, whereas 8 plants row m-1 were necessary to reduce yield when herbicides were used. Herbicide use also increased soybean yield at higher sicklepod densities. Chlorimuron plus metribuzin reduced sicklepod dry matter at 8 plants row m-1. To maintain soybean yield, a weed-free period of 4 wk after emergence was required, regardless of treatment. Both herbicide treatments resulted in increased soybean yield at the zero and two wk weed-free periods; however, they did not affect soybean yield when the weed-free period was 4 wk or more. Imazaquin reduced sicklepod density when plots were left weedy full-season, and further reductions were noted with chlorimuron plus metribuzin. A sicklepod weedy interval of 8 wk reduced soybean yield when untreated, but either herbicide treatment extended that interval to 16 wk.

Several precision postemergence-directed sprayers with different nozzle designs and arrangements were evaluated for potential use in sweet corn for wild-proso millet (PANMI) control in field trials from 1987 to 1989. Ametryn at 2270 g ha-1 plus oil-emulsifier mixture (OEM) at 1.3% v/v and sethoxydim alone or plus OEM applied postemergence-directed selectively controlled PANMI in sweet corn. Sethoxydim at 220 g ha-1 plus OEM controlled PANMI best when averaged over the 3-yr period. Ametryn plus OEM did not injure corn and sethoxydim at 110 g ha-1 plus OEM caused little or no corn injury and no yield reductions when applied with any of the sprayers. Generally, only sethoxydim at 220 g ha-1 plus OEM injured corn. The amount of injury was different among sprayers, with the nozzle designs and arrangements responsible for corn injury. Injury was minimized when sethoxydim was applied with a sprayer equipped with 150 degree dual orifice nozzles spaced 38 cm apart and mounted on skids that contacted the soil to assure constant nozzle height. This sprayer, or sprayers of similar nozzle design, show the most potential for use by sweet corn growers.

Research trials conducted at two locations in the spring of 2004 evaluated the effect of soil temperature as an indicator for application timings of certain sulfonylurea herbicides for perennial ryegrass control while maintaining acceptable turfgrass quality during bermudagrass spring transition. Herbicide application timings began when soil temperatures reached 17 C (April 14, 2004). Greater perennial ryegrass control 4 wk after initial treatment (WAIT) was achieved when sulfonylurea herbicides were applied at 26 C soil temperature compared to 17 or 21 C. Bermudagrass density 6 WAIT increased with treatments applied at 26 C soil temperature compared to cooler soil temperatures. There was a decrease in overall turfgrass quality 2 WAIT when treatments were applied at 17 C. However, by 4 WAIT all application timings provided overall turfgrass quality comparable to the untreated control. Acceptable turfgrass quality and maximum perennial ryegrass control was achieved by delaying transition-aid herbicide applications until soil temperatures reached 26 C and growing conditions were more conducive to bermudagrass growth.

A decision criterion is presented for postemergence johnsongrass control in soybeans. Models derived from actual data describing the relationship between johnsongrass density (X) and soybean yield loss are used to develop the decision criterion for soybeans planted in 0.25- and 1-m row spacings. The yield loss equations are L1 = 424–424 exp (-0.023X2) for 0.25-m row spacing and L2 = 643-643 exp (−0.004X2) for 1-m row spacing. When combined with the cost of control (Px) and the expected price of soybeans (Py), these equations can be used to find the density thresholds where johnsongrass control becomes profitable. For the 0.25-m row spacing, this relationship was Px = Py [424–424 exp (−0.023X2) or more simply Px = Py L1, which equates the cost of control to the value of the soybean yield increase from control. The johnsongrass density (X) that satisfies this equality is the threshold (X*) above which control is profitable.

Field and greenhouse experiments were conducted to determine the effect of selected insecticides on cotton when applied in combination with pyrithiobac. In the field, acephate, azinphos-methyl, bifenthrin, chlorpyrifos, dicrotophos, esfenvalerate, malathion, methomyl, or oxamyl was applied foliarly with the sodium salt of pyrithiobac at 70 g ae/ha. Pyrithiobac plus malathion resulted in greatest injury when compared with other treatments. There were no differences observed in fruiting characteristics of cotton. Cotton yield was lower with oxamyl, methomyl, and chlorpyrifos when applied in combination with pyrithiobac in one of three experiments. In greenhouse experiments, injury due to pyrithiobac was greater in a cool (21 C day, 13 C night) temperature than in a warm temperature (30 C day, 21 C night), but differences were less than 15%. Pyrithiobac plus malathion in the cool environment injured cotton more severely 7 DAT than either pesticide alone. Adding insecticides to pyrithiobac did not influence injury in the warm environment.

An experiment was conducted to evaluate the translocation pattern of 14C-glyphosate and 14C-quizalofop in five quackgrass biotypes at two stages of growth. Whole plant translocation differed between stages for each herbicide. The percentage of 14C-glyphosate and 14C-quizalofop in the leafwash and in the treated leaf did not differ among biotypes, but differences occurred for the translocation to the underground parts. The partitioning of the 14C-glyphosate and 14C-quizalofop in the treated crown, other crowns, propagating rhizomes, and other rhizomes differed among biotypes. On a disintegration per minute (DPM) mg-1 basis, differences among biotypes were found with 14C-glyphosate but much less with 14C-quizalofop. Metabolism of 14C-quizalofop in the treated leaf was similar in the two biotypes tested except for the percentage of polar metabolites 1 d after treatment. The percentage of 14C-quizalofop available for translocation was the same in both biotypes.

Research was conducted in 2006 and 2007 to evaluate nicosulfuron tank-mixes for field sandbur control and crop injury to ‘Tifton 85’ and ‘Jiggs’ bermudagrass. In 2006, sequential applications of nicosulfuron + metsulfuron controlled field sandbur 86 to 90% 30 d after treatment (DAT) and 77 to 85% 90 DAT. Single applications of nicosulfuron provided less than 63% control 90 DAT. In 2007, sequential applications of nicosulfuron + metsulfuron controlled field sandbur 84 to 95% 42 DAT. Injury data showed Jiggs bermudagrass was generally more sensitive to herbicide treatment than Tifton 85. Injury to Tifton 85 bermudagrass ranged from 0 to 15%, whereas injury to Jiggs was 7 to 29% 22 DAT. Forage yield data for Jiggs showed significant reductions at the first and second harvests but no differences by the third harvest. No yield reduction was noted for Tifton 85 bermudagrass from any herbicide treatment. Results of these studies indicate that nicosulfuron + metsulfuron combinations are a viable option for field sandbur control in bermudagrass pastures.

The effect of season-long interference by bands of weeds growing only between rows (BR) on field corn yields has not been reported before or compared with weedy and weed-free (i.e., weeded) plots or bands of weeds growing only in row (IR). The null hypothesis of this research was that field corn yields would be ranked as weed-free > BR weedy only > IR weedy only > weedy (IR + BR weedy) in response to season-long weed interference by these four treatments. Weeds growing as bands closest to field corn were expected to reduce field corn yields more than those growing as bands further away between field corn rows. Field corn yield response to these four weed interference treatments was studied in Missouri for 4 yr. In late summer, most weed ground cover consisted of giant foxtail, the chief weed present, and common waterhemp, a lesser weed. Observed field corn yields averaged for 4 yr were ranked as weed-free > IR weedy only > BR weedy only > weedy. Field corn yields of the IR weedy only, BR weedy only, and weedy treatments averaged 76, 63, and 41%, respectively, of the weed-free treatment (=7,820 kg/ha). In two of the 4 yr, field corn yield of the IR weedy treatment exceeded that of the BR weedy treatment, whereas these treatments could not be statistically distinguished from one another in the other 2 yr. These research results refute the null hypothesis and demonstrate that it may be more critical to control BR than IR weeds, although controlling both BR and IR weeds maximized field corn yields.

Cold stress and field studies were conducted to determine the effects of alachlor, metolachlor, butylate plus dichlormid, and EPTC plus dichlormid on germination and seedling vigor of 30 sweet corn cultivars with three commercially important endosperm mutants (su, se, and sh2). Seedling emergence from cool soils was best when treated with EPTC plus dichlormid and alachlor and was decreased 11% by metolachlor and butylate plus dichlormid. The se and sh2 endosperm mutants were injured the most by the herbicides. Plant size was reduced by the thiocarbamate herbicides but not by the chloracetamides.