Paclobutrazol and flurprimidol were evaluated for suppression of a perennial subspecies of annual bluegrass in a creeping bentgrass green. Three applications of paclobutrazol in the spring (Mar. 17, Apr. 17, and May 17) followed by three applications in the fall (Oct. 2, Nov. 2, and Nov. 30) suppressed the perennial subspecies ≥ 72% at 3 wk after the final treatment. However, suppression was reduced to ≤ 57% by 4 mo after the final fall application. Flurprimidol applied in three spring and three fall applications did not suppress the perennial subspecies as effectively as paclobutrazol. Suppression was ≤ 47% at 3 wk after the final flurprimidol treatment and was only ≤ 20% by mid-March. Neither chemical injured creeping bentgrass greater than 20% in the spring. However, leaf discoloration injury from the initial October application ranged from 26 to 30% for paclobutrazol in 1993 and 21 to 28% for flurprimidol in 1994. When injury occurred in October it was temporary and the creeping bentgrass recovered within 3 to 4 wk. Paclobutrazol and flurprimidol applied in November did not injure creeping bentgrass.

Field studies were conducted to identify herbicides suitable for improved control of hairy nightshade, redroot pigweed, and common lambsquarters in pinto beans. Fomesafen at 0.25 kg ai ha-1 did not adequately control these weeds. Clomazone at 0.5 kg ai ha-1 controlled common lambsquarters but only suppressed the growth of redroot pigweed and hairy nightshade. Ethalfluralin at 0.84 to 1.1 kg ai ha-1 gave excellent initial control of these weeds but did not control later flushes of hairy nightshade. Imazethapyr applied PPI or POST at 50 to 75 g ai ha-1 controlled hairy nightshade, redroot pigweed, and common lambsquarters throughout the growing season. Imazethapyr combined with ethalfluralin gave superior weed control and resulted in greater yields than the most commonly used herbicides in pinto beans in western Canada.

The postemergence herbicide ethofumesate and the plant growth regulator paclobutrazol were evaluated for annual bluegrass control in creeping bentgrass turf managed as golf fairways. Both products were applied under several different timing regimes relative to the time of the year. Paclobutrazol treatments provided significantly greater annual bluegrass control than ethofumesate. There were no differences between rates of paclobutrazol (0.28 and 0.14 kg ai/ha) when applied from spring through summer. Annual bluegrass control after spring and summer applications of paclobutrazol was 85% or more. Clipping weight data indicated that paclobutrazol suppressed growth in annual bluegrass longer than in creeping bentgrass. It was concluded that prolonged suppression of annual bluegrass by paclobutrazol resulted in creeping bentgrass dominance and subsequent annual bluegrass control. Additionally, applications of ethofumesate in autumn–winter, followed by paclobutrazol applied in spring–summer, provided significant control of annual bluegrass in 1 yr of the study.

Harvest weed seed control (HWSC) systems have been developed to exploit the high proportions of seed retained at maturity by the annual weeds rigid ryegrass, wild radish, bromegrass, and wild oats. To evaluate the efficacy of HWSC systems on rigid ryegrass populations, three systems, the Harrington Seed Destructor (HSD), chaff carts, and narrow-windrow burning were compared at 24 sites across the western and southern wheat production regions of Australia. HWSC treatments were established at harvest (Nov. – Dec.) in wheat crops with low to moderate rigid ryegrass densities (1 to 26 plants m−2). Rigid ryegrass counts at the commencement of the next growing season (Apr. – May) determined that HWSC treatments were similarly effective in reducing emergence. Chaff carts, narrow-windrow burning, or HSD systems act similarly on rigid ryegrass seed collected during harvest to deliver substantial reductions in subsequent rigid ryegrass populations by restricting seedbank inputs. On average, population densities were reduced by 60%, but there was considerable variation between sites (37 to 90%) as influenced by seed production and the residual seedbank. Given the observed high rigid ryegrass seed production levels at crop maturity it is clear that HWSC has a vital role in preventing seedbank inputs in Australian conservation cropping systems.

A field study was conducted in 2007 and 2008 near Murphysboro, IL to determine the effect of plant height and addition of glyphosate on control of glyphosate-resistant horseweed with saflufenacil. Saflufenacil was applied at rates ranging from 25 to 125 g ai ha−1 alone and in combination with glyphosate at 840 g ae ha−1, and the efficacy compared to paraquat at 840 g ai ha−1. Control of horseweed with glyphosate applied alone was less than 30%, confirming the presence of glyphosate-resistant plants. At 14 d after application, all treatments with saflufenacil or paraquat provided at least 90% control. Saflufenacil applied alone at the lowest rate of 25 g ha−1 provided less control (92%) than all other treatments that included saflufenacil, and efficacy was reduced as horseweed height at application increased. Horseweed control from saflufenacil at 50 g ha−1 was reduced as plant height increased in 2007 but not in 2008. However, saflufenacil applied at 50 g ha−1 or greater resulted in at least 98% control, regardless of horseweed height at application or tank mixture with glyphosate. Combining glyphosate with saflufenacil at 25 g ha−1 increased horseweed control compared with saflufenacil applied alone and resulted in control similar to saflufenacil applied at 50 g ha−1. Control of horseweed from paraquat declined over time as the growth continued from the apical meristem. The extent of horseweed regrowth from applications of saflufenacil alone was less than that observed from paraquat. The addition of glyphosate to saflufenacil further reduced the frequency of horseweed regrowth compared with saflufenacil applied alone.

Increasing the pH of the spray water to solubilize the weak acid herbicide nicosulfuron and then decreasing pH below its pKa so that it converts into a neutral form enhances biological activity under some conditions. The water-dispersible granule formulation of nicosulfuron starts as dispersed particles. Adding 1% wt/wt K3PO4 solubilizes nicosulfuron and increases its activity compared to its dispersion without base. The type of buffer and the surfactant HLB or hydrophilic lipophilic balance, a measure of the molecular balance of the hydrophilic and lipophilic groups, altered the activity of nicosulfuron. Adding 1% wt/wt K3PO4 increases the pH, and the optimum HLB ranged from 13 to 17 on large crabgrass. Adding 1% wt/wt H3PO4 reduces the pH and lowers the optimum HLB range from 10 to 14 on large crabgrass. Adding the acidic buffer converts the solubilized nicosulfuron into its neutral form and increases activity under some surfactant conditions. Thus, neutral nicosulfuron is more active with lipophilic surfactants, while ionic nicosulfuron is more active with hydrophilic surfactants. When tested on other species, low HLB surfactants are the most active at low pH. These results support the concept that the physicochemical properties of the herbicide, adjuvants, and weed species should be matched for optimum activity.

The recent interest in cover crops as component of Midwest corn and soybean production systems has led to the need for additional research, including the effects of residual corn and soybean herbicide treatments on fall cover crop establishment. Field studies were conducted in 2013, 2014, and 2015 in Columbia, Missouri to investigate the effects of common residual herbicides applied in corn and soybean on establishment of winter wheat, tillage radish, cereal rye, crimson clover, winter oat, Austrian winter pea, Italian ryegrass, and hairy vetch. Cover crops were evaluated for stand and biomass reduction 28 d after emergence (DAE). Rainfall from herbicide application to cover crop seeding date was much greater in 2014 and 2015, which resulted in less carryover in these years compared to 2013. When averaged across all herbicides evaluated in these experiments, the general order of sensitivity of cover crops to herbicide carryover, from greatest to least was Austrian winter pea=crimson clover>oilseed radish>Italian ryegrass>hairy vetch>wheat >winter oat>cereal rye. Cereal rye had the fewest instances of biomass or stand reduction with only four out of the 27 herbicides adversely effecting establishment. Pyroxasulfone consistently reduced Italian ryegrass and winter oat biomass at least 67% in both the corn and soybean experiments. In the soybean experiment, imazethapyr- and fomesafen-containing products resulted in severe stand and biomass reduction in both years while flumetsulam-containing products resulted in the greatest carryover symptoms in the corn experiment. Results from these experiments suggest that several commonly used corn and soybean herbicides have the potential to hinder cover crop establishment, but the severity of damage will depend on weather, cover crop species, and the specific herbicide combination.

Reflectance data were subjected to a variety of analysis methods to determine the utility of hyperspectral reflectance for differentiating soybean, soil, and six weed species commonly found in Mississippi agricultural fields. Weed species evaluated were hemp sesbania, palmleaf morningglory, pitted morningglory, prickly sida, sicklepod, and smallflower morningglory. Hyperspectral reflectance data were collected from mature plant leaves three times in 2002 and two times in 2003. Vegetation indices were calculated and subjected to principal component analysis (PCA) and linear discriminant analysis (LDA). The PCA, using vegetation indices, produced the poorest classification accuracies for the plant species studied, generally less than 50%, whereas LDA resulted in classification accuracies greater than those from PCA. Best spectral band combination (BSBC) provided the greatest classification accuracies, with all better than 80% for all data sets. The BSBC indicated three wavelength bands of interest for species discrimination in the short wavelength infrared portion of the electromagnetic spectrum, which are not commonly used in current vegetation indices for species differentiation. These areas of interest were located from 1,445 to 1,475 nm, 2,030 to 2,090 nm, and 2,115 to 2,135 nm. The top 10 wavelengths determined by BSBC were then added to the vegetation indices and reanalyzed using PCA and LDA. Classification accuracies increased for all species when these wavelengths were added rather than using vegetation indices alone, suggesting greater crop and weed species differentiation can be obtained when using sensors that include these wavelength regions of the short wavelength infrared portion of the electromagnetic spectrum.

Saflufenacil and indaziflam, POST and PRE herbicides, respectively, have been registered recently for weed control in Florida citrus. Glufosinate is under evaluation and may be registered in the future for POST weed control in citrus. Citrus growers often want to have a tank mixture of herbicides that provide broad-spectrum weed control. Saflufenacil is a broadleaf herbicide and needs to be tank mixed with other herbicide(s) to increase weed control spectrum. Information is not available on interaction of saflufenacil, glufosinate, and indaziflam applied in tank mixtures on weed control efficacy. Greenhouse and field experiments were conducted at two locations (Polk and Orange County, FL) to evaluate the efficacy and potential antagonism or synergy of saflufenacil and glufosinate applied in tank mixes, and various three-way mixes with indaziflam. The results suggested that tank mixing saflufenacil with glufosinate had no effect on grass weed control, but had additive effect on broadleaf weed control. Indaziflam tank mixed at the recommended label rate (0.073 kg ha−1) provided better residual weed control compared with the lower rate (0.05 kg ha−1). Tank mixing indaziflam with saflufenacil and glufosinate improved broadleaf and grass weed control, reduced weed density, and biomass compared with tank mixing saflufenacil and glufosinate. Tank mixing indaziflam at 0.073 kg ha−1 with saflufenacil and glufosinate provided ≥ 88% control of broadleaf and grass weeds at 30 d after treatment (DAT), and it was comparable with tank mixing saflufenacil, glyphosate and pendimethalin. This treatment combination recorded the lowest weed density (≤ 7 plants m−2) and biomass (< 80 g m−2) at 60 DAT. Glyphosate applied alone was less effective than tank mixing with saflufenacil and glufosinate for broadleaf and grass weed control. This indicates additive effect of tank mixture on glyphosate efficacy. It is concluded that saflufenacil can be tank mixed with glufosinate for control of broadleaf and grass weeds; however, addition of indaziflam in tank mixture provided long-term, broad-spectrum weed control in Florida citrus compared with other treatments.

Glyphosate effectively controls most weeds in glyphosate-resistant soybean. However, it is sometimes only marginally effective on Ipomoea spp. A field experiment was conducted at five locations in North Carolina to determine the effects of mixing 2,4-DB with glyphosate on Ipomoea spp. control and on soybean injury and yield. The isopropylamine salt of glyphosate at 560, 840, and 1,120 g ai/ha controlled mixtures of tall morningglory, entireleaf morningglory, and red morningglory at least 96% at two locations. Mixing the dimethylamine salt of 2,4-DB at 35 g ae/ha with glyphosate did not increase control but reduced soybean yield 6%. At two other locations, 2,4-DB increased control of tall morningglory and a mixture of entireleaf morningglory and ivyleaf morningglory 13 to 22% when mixed with glyphosate at 560 g/ha, but not when mixed with glyphosate at 840 or 1,120 g/ha. Soybean yield was reduced 31% at one location and was unaffected at the other. At the fifth location, 2,4-DB increased control of tall morningglory 25, 11, and 7% when mixed with glyphosate at 560, 840, and 1,120 g/ha, respectively. Soybean yield was increased 15%. In separate field experiments, glyphosate at 560, 840, and 1,120 g/ha controlled large crabgrass at least 99%. Mixing 2,4-DB at 35 g/ha with glyphosate did not affect control. In the greenhouse, mixing 2,4-DB at 35, 70, 140, or 280 g/ha with glyphosate at 70 to 560 g/ha did not affect large crabgrass control by glyphosate.

Field experiments were conducted in 1983 and 1984 at two locations to determine the influence of various densities and durations of kochia interference in sunflower. Sunflower achene yield and dry weight were reduced by all densities of kochia, averaged over locations and years. Season-long competition by kochia densities of 0.3, 1, 3, and 6 plants/m of row decreased sunflower achene yield 7, 10, 20, and 27%, respectively. Sunflower achene yield and sunflower dry weight decreased as weeks of kochia competition increased. Only 2 weeks of kochia competition after sunflower emergence decreased sunflower achene yield 6%. Sunflower achene yield loss increased as the duration of kochia competition increased. Sunflower 200 achene weight, oil content, and plant height were not influenced by various densities or durations of kochia competition.

Greenhouse studies were conducted in 2003 at the Stine–Haskell Research Center to determine whether herbicide inhibitors of six specific sites in the carotenoid biosynthesis pathway would elicit synergistic responses when applied postemergence (POST) in combination with the photosystem II (PSII) inhibitor atrazine. Based on data analysis with the Isobole method, synergistic responses were observed on red morningglory, common cocklebur, and giant foxtail when atrazine was applied in mixtures with the deoxy-D-xylulose-5-phosphate reductoisomerase (DOXP reductoisomerase) inhibitor fosmidomycin, the p-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor mesotrione, and the DuPont proprietary zeta-carotene desaturase (ZDS) inhibitor DFPC. Clomazone (its metabolite ketoclomazone is the actual enzyme inhibitor), an inhibitor of 1-deoxy-D-xylulose-5-phosphate synthatase (DOXP synthase), provided synergistic responses on red morningglory, but antagonistic responses on both common cocklebur and giant foxtail when applied in mixtures with atrazine. Combinations of the lycopene cyclase (LC) inhibitor, CPTA, with atrazine produced synergistic responses on both common cocklebur and giant foxtail but were antagonistic on red morningglory. Norflurazon, a phytoene desaturase (PDS) inhibitor, applied in mixtures with atrazine provided synergistic responses on red morningglory, antagonistic responses on giant foxtail, and independent responses on common cocklebur. Because carotenoids have been determined to play a key role in quenching singlet oxygen species in the chloroplast and also assist in the maintenance of the D1 protein in PSII, this might help explain the synergistic responses with atrazine observed in our studies.

A field study was conducted in 2015 and 2016 to compare particle drift of glyphosate using a fluorescent tracer dye applied with hooded and open sprayers at four spray qualities (Fine [F], Medium [M], Very-Coarse [VC], and Ultra-Coarse [UC]). F and M spray qualities exhibited up to 86% and 56% less drift, respectively, out to 31 m downwind with the hooded sprayer than with the open sprayer. Conversely, VC and UC spray qualities were not affected by sprayer type out to 31 m downwind. From 43 to 104 m downwind, hooded sprayer applications exhibited approximately 50% less drift than open sprayer applications, regardless of spray quality. From 43 to 89 m downwind, F spray qualities, regardless of sprayer type, exhibited higher drift than all other spray qualities. These data indicate that hooded sprayers considerably reduce drift of all spray qualities at short distances downwind. Additionally, at longer distances downwind, both larger spray qualities and sprayer hoods reduced drift independently.

Field experiments were conducted to evaluate the effect of five spray-nozzle types and three drift-control adjuvants (DCA) on glyphosate spray drift. The extended-range (XR) flat-fan nozzle at 280 kPa was used as the standard comparison. DCAs were evaluated for drift reduction with the use of the XR and air-induction (AI) nozzles. Wind speed ranged from 1.3 to 9.4 m/s (3 to 21 mph). Lethal drift (DL) and injury drift (DI) were determined by downwind visual observation of grain sorghum response. Drift distances were measured from the spray swath edge. The Turbo FloodJet and AI nozzles reduced DL distance by 34%. All four drift-reducing (DR) nozzles reduced DI distance by 22 to 32%. Reducing the pressure of the XR flat-fan nozzle from 280 to 140 kPa did not reduce DL or DI distance. When applied through AI nozzles, each DCA increased droplet volume diameter, one DCA reduced DI distance and none reduced DL distance when applied through XR tips. The DCAs did not affect DL or DI distance.

Time of day at which a herbicide is applied can affect efficacy, and variability may be attributed to leaf angles at application. Spray interception by hemp sesbania (Sesbania exaltata), sicklepod (Senna obtusifolia), and prickly sida (Sida spinosa) under day and night conditions was quantified by measuring interception of a 2-M potassium nitrate solution. Following the night application, interception by prickly sida, hemp sesbania, and sicklepod was reduced 17, 67, and 70%, respectively. In a second study in the greenhouse, glyphosate was applied to hemp sesbania, pitted morningglory (Ipomoea lacunosa), prickly sida, and sicklepod at 6:00 and 11:00 A.M. and 4:00 and 9:00 P.M. Control of all species was dependent on the time of day treated, with night applications generally being less effective.

Feral rye, commonly referred to as cereal, winter, common, or volunteer rye, is an important weed in winter wheat production in many parts of the United States and the world. Feral rye reduces net profits in the United States by more than $27 million due to lower grain yields, increased dockage, and reduced land values. To date, limited research has been conducted on components that make feral rye a problem in various cropping systems. Herbicide-tolerant wheat technology can be used to manage feral rye, but current efficacy levels are not adequate for high feral rye densities. In addition, the long-term effects that individual management strategies may have on feral rye populations are unknown. This review addresses the physical, environmental, and genetic characteristics of Secale cereale. Current economic impact, management, and research data gaps are also discussed.

Studies were conducted to determine the effectiveness of 11 multiple treatment combinations of bensulide in controlling a perennial and an annual subspecies of annual bluegrass. Bensulide controlled 97% of the annual subspecies with annual applications of 11 kg ai ha–1 (Jan.) + 6 kg ha–1 (Feb.) + 6 kg ha–1 (Mar.) totaling 92 kg ha–1 in 4 yr. The annual subspecies appeared to have a germination period from mid November to early January. None of the bensulide treatments controlled the perennial subspecies acceptably. The common occurrence of these two subspecies in mixed stands may account for the erratic weed control reported by many researchers. Bentgrass showed good tolerance to bensulide totals over 4 yr of 160 kg ha–1 applied in a U.S. Golf Association rootzone green.

Sulfentrazone adsorption and mobility in six soils with varying soil properties were evaluated under laboratory conditions. Adsorption was evaluated using a modified slurry technique. Mobility was evaluated using packed-soil columns under saturated flow conditions. The order of adsorption to soil was Sequatchie loam > Dothan loamy sand = Bosket fine sandy loam > Malden loamy sand > Commerce silty clay loam > Harkey clay loam. Greater sulfentrazone adsorption occurred in soils with lower pH. Sulfentrazone movement under saturated flow conditions in 27-cm soil-packed columns was greater in soils with low adsorption, high pH, and coarse texture. Sulfentrazone movement was limited in the Sequatchie loam but was greater in the other soils examined. No clear relationship was evident between sulfentrazone mobility and adsorption in these soils.

Response of creeping bentgrass, annual bluegrass, and Kentucky bluegrass to foliar, soil, or foliar plus soil applications of bispyribac-sodium was evaluated in greenhouse studies. Soil-alone and foliar plus soil applications of bispyribac-sodium at 148 or 296 g ai/ha resulted in greater injury and shoot dry weight reduction of all species 28 d after treatment (DAT) compared to foliar-alone treatments. Creeping bentgrass was less injured than annual or Kentucky bluegrass regardless of application placement. Further studies evaluated foliar and root absorption and translocation of 14C-bispyribac-sodium in creeping bentgrass, annual bluegrass, Kentucky bluegrass, and roughtstalk bluegrass. Foliar absorption into creeping bentgrass was less than that of other species at most harvest timings from 4 to 72 h after treatment. Annual and roughstalk bluegrass translocated greater amounts of foliar-absorbed 14C to the crown and shoots compared to creeping bentgrass. Annual and roughstalk bluegrass accumulated approximately 47% more 14C per dry weight of plant tissue than creeping bentgrass and 74% more than Kentucky bluegrass after 72 h in nutrient solution containing 14C-bispyribac-sodium. Annual and roughstalk bluegrass translocated approximately 80% of root-absorbed 14C to shoots, whereas creeping bentgrass and Kentucky bluegrass translocated slightly less (66% of absorbed for both species). These studies suggest that bispyribac-sodium is readily absorbed by roots and translocated to shoots which may contribute to its total activity within a plant. In addition, creeping bentgrass displayed lower amounts of foliar and root absorption and subsequent translocation than annual and roughstalk bluegrass which may contribute to greater bispyribac-sodium tolerance displayed by creeping bentgrass.

Herbicides registered for lima bean (Phaseolus lunatus L.) do not consistently control many troublesome weeds. Some herbicides registered for soybean (Glycine max) will control these weeds, but tolerance to lima bean is not known. Two field and two greenhouse studies were conducted to evaluate recently registered soybean herbicides for lima bean tolerance. Field studies were conducted in Delaware from 1996 to 1998, and in North Carolina during 1997 and 1998. The first field study evaluated the preemergence (PRE) herbicides cloransulam at 0.01, 0.02, 0.03, and 0.04 kg ai/ha; flumetsulam at 0.04, 0.05, 0.06, and 0.07 plus metolachlor at 1.3, 1.6, 1.8, and 2.1 kg ai/ha; sulfentrazone at 0.1, 0.15, 0.2, and 0.25 kg ai/ha; lactofen at 0.2 and 0.25 kg ai/ha; and the commercial standard treatment of imazethapyr plus metolachlor at 0.05 and 1.7 kg ai/ha, respectively. Lima bean injury 5 to 8 wk after emergence was lowest for imazethapyr plus metolachlor (standard treatment) and all four rates of cloransulam. Crop injury with flumetsulam plus metolachlor ranged from 0 to 18% and sulfentrazone ranged from 3 to 75% depending on location and rate. Lactofen treatments caused unacceptable lima bean injury. Yield in plots treated with cloransulam were consistently greater than in the plots treated with other herbicides. The second field study examined the postemergence (POST) herbicides cloransulam (0.013 or 0.02 kg ai/ha), bentazon (1.1 kg ai/ha), imazethapyr (0.035 or 0.053 kg ai/ha), and imazamox (0.018 or 0.036 kg ai/ha), applied when the crop was at the first trifoliolate stage. Cloransulam caused 0 to 13% crop injury and imazamox caused 3 to 25% injury depending on rate and location. In greenhouse studies, no differences were observed among eight common processing lima bean cultivars in tolerance to sulfentrazone applied PRE or to cloransulam, imazamox, imazethapyr, or bentazon applied POST.