Tall fescue is susceptible to injury from many acetolactate synthase (ALS) inhibitors used for broadleaf weed control in turfgrass. Florasulam is an ALS inhibitor that selectively controls broadleaf weeds in tall fescue, but the mechanisms for selectivity are not well understood. The objective of this research was to evaluate the physiological basis of tall fescue tolerance to florasulam. In greenhouse experiments, florasulam rates required to injure tall fescue 20% (I₂₀) and white clover 80% (I₈₀) measured 320 and 65 g ai ha^-1, respectively. The I₂₀ and I₈₀ values of another ALS inhibitor, flucarbazone, on these species measured 33 and 275 g ai ha^-1, respectively. In laboratory experiments, the time required to reach 50% foliar uptake for ¹⁴C-florasulam and ¹⁴C-flucarbazone measured 23 and 62 h for white clover, respectively, and >72 h for both herbicides in tall fescue. The half-lives of florasulam and flucarbazone in tall fescue were 15 and 40 h, respectively, whereas the half-life in white clover was >72 h for both herbicides. The concentrations of florasulam and flucarbazone required to inhibit ALS enzymes 50% in excised leaves of tall fescue measured >1,000 and 32 µM, respectively. The selectivity of florasulam for white clover control in tall fescue is associated with differential levels of absorption and metabolism between species. Tall fescue has faster metabolism and less ALS enzyme inhibition from florasulam as compared to a more injurious ALS inhibitor, flucarbazone, which contributes to the differential tolerance levels between these herbicides.

Nomenclature: Florasulam; flucarbazone-sodium; tall fescue, Festuca arundinacea Shreb.; white clover, Trifolium repens L.

Rush skeletonweed is emerging as a regionally important weed of winter wheat production in eastern Washington. Field studies were conducted during the 2016 and 2017 crop years to evaluate several auxin herbicides applied at two seasonal timings (fall or spring) for control of rush skeletonweed in winter wheat. Clopyralid (210 g ae ha^-1) provided >90% visual control of rush skeletonweed in both years of the study and aminopyralid (10 g ae ha^-1) provided >80% visual control. Aminocyclopyrachlor, dicamba, and 2,4-D provided <55% control of rush skeletonweed. Season of application did not meaningfully affect efficacy of any herbicide tested. Wheat yields were reduced by 39 to 69% compared to the non-treated check when aminocyclopyrachlor was applied in the spring. Clopyralid is an effective option for control of rush skeletonweed in Pacific Northwest winter wheat.

Nomenclature: Aminocyclopyrachlor; aminopyralid; clopyralid; dicamba; 2,4-D; rush skeletonweed, Chondrilla juncea L.; wheat, Triticum aestivum L.

Field experiments were conducted in 2014 and 2015 in Fayetteville, Arkansas, to evaluate the residual activity of acetyl-CoA carboxylase (ACCase)-inhibiting herbicides for monocot crop injury and weed control. Conventional rice, quizalofop-resistant rice, grain sorghum, and corn crops were evaluated for tolerance to soil applications of six herbicides (quizalofop at 80 and 160 g ai ha^-1, clethodim at 68 and 136 g ai ha^-1, fenoxaprop at 122 g ai ha^-1, cyhalofop at 313 g ai ha^-1, fluazifop at 210 and 420 g ai ha^-1, and sethoxydim at 140 and 280 g ai ha^-1). Overhead sprinkler irrigation of 1.3 cm was applied immediately after treatment to half of the plots, and the crops planted into the treated plots at 0, 7, and 14 d after herbicide treatment. In 2014, injury from herbicide treatments increased with activation for all crops evaluated, except for quizalofop-resistant rice. At 14 d after treatment (DAT) in 2014, corn and grain sorghum were injured 19% and 20%, respectively, from the higher rate of sethoxydim with irrigation activation averaged over plant-back dates. Conventional rice was injured 13% by the higher rate of fluazifop in 2014. Quizalofop-resistant rice was injured no more than 4% by any of the graminicides evaluated in either year. In 2015, a rainfall event occurred within 24 h of initiating the experiment; thus, there were no differences between activation via irrigation or by rainfall. However, as in 2014, grain sorghum and corn were injured 16% and 13%, respectively, by the higher rate of sethoxydim, averaged over plant-back dates. All herbicides provided little residual control of grass weeds, mainly broadleaf signalgrass and barnyardgrass. These findings indicate the need to continue allowing a plant-back interval to rice following a graminicide application, unless quizalofop-resistant rice is to be planted. The plant-back interval will vary by graminicide and the amount of moisture received following the application.

Nomenclature: Clethodim; cyhalofop; fenoxaprop; fluazifop; quizalofop; sethoxydim; barnyardgrass, Echinochloa crus-galli (L.) Beauv.; broadleaf signalgrass, Urochloa platyphylla (Munro ex C. Wright) R.D. Webster; corn, Zea mays L.; grain sorghum, Sorghum bicolor (L.) Moench.; rice, Oryza sativa L.

Benzobicyclon will be the first 4-hydroxyphenylpyruvate dioxygenase (HPPD)–inhibiting herbicide available in US rice production pending registration completion. An observation of benzobicyclon controlling weedy rice in two field trials prompted a greenhouse and field evaluation to determine if benzobicyclon would control weedy rice accessions from Arkansas, Mississippi, and southeastern Missouri. A total of 100 accessions were screened in the greenhouse and field. Percentage mortality was determined in the greenhouse, and percentage control was recorded in the field. Benzobicyclon at 371 g ai ha^-1 caused at least 80% mortality of 22 accessions in the greenhouse and at least 80% control of 30 accessions in the field. For most accessions, individual plants within the accession varied in response to benzobicyclon. Based on these results, the sensitivity of weedy rice to benzobicyclon varies across accessions collected in the midsouthern United States, and it may provide an additional control option for weedy rice in some fields.

Nomenclature: Benzobicyclon; weedy rice, Oryza sativa L.; rice, Oryza sativa L.

Six trials were conducted during 2014/15 and 2015/16 growing seasons in Brazil to determine the effect of 2,4-D formulations and spray nozzles on 2,4-D spray drift under conventional field conditions. An experimental 2,4-D choline formulation with Colex-D® Technology (GF-3073) and a 2,4-D dimethylamine (DMA) formulation were applied with either XR and AIXR flat-fan spray nozzles. Each plot was 30m wide by 24m long (720m²) with 60 glyphosate-resistant soybean rows spaced 50 cm apart and also 35 potted tomato plants distributed on a grid across the plot 5-m apart. Applications were performed one meter away from the plot edge perpendicular to the soybean rows when wind direction was parallel to the rows with less than 30 degrees of angle deviation. Spray drift treatments were applied in 100 L ha^-1 with tractor sprayers at 276 kPa equipped with a 7-m wide boom at 50 cm above the canopy of the soybean plant, operating at 6.8 km h^-1. The distance from the plot edge to the farthest plant with 2,4-D symptoms was assessed for every four soybean rows at 10 and 20 days after treatment (DAT) and potted tomatoes at 10 DAT. GF-3073 reduced the distance of the farthest injured plant with 2,4-D symptoms compared to the 2,4-D DMA formulation regardless of the spray nozzle, assessment date and sensitive species. GF-3073 applied through the AIXR nozzle reduced the relative drift affected area to the standard by 68% at 10 DAT and 67% at 20 DAT for soybean and 60% at 10 DAT for potted tomatoes.

Nomenclature: 2,4-D; soybean, Glycine max (L.) Merr.; tomato, Solanum lycopersicum L.

Sugarbeet, grown for biofuel, is being considered as an alternate cool-season crop in the southeastern U.S. coastal plain. Typically, the crop would be seeded in the autumn, then grow through the winter and be harvested the following spring. Labels for herbicides registered for use on sugarbeet grown in the traditional sugarbeet production regions do not list any of the cool-season weeds common in the southeastern United States. Field trials were initiated near Ty Ty, GA, to evaluate all possible combinations of ethofumesate applied PRE, phenmedipham desmedipham applied POST, clopyralid POST, and triflusulfuron POST for cool-season weed control in sugarbeet. Phenmedipham desmedipham alone and in combination with clopyralid and/or triflusulfuron effectively controlled cutleaf eveningprimrose, lesser swinecress, henbit, and corn spurry when applied to seedling weeds. Ethofumesate PRE alone was not as effective in controlling cool-season weeds compared to treatments containing phenmedipham desmedipham POST. However, ethofumesate PRE applied sequentially with phenmedipham desmedipham POST improved weed control consistency. Clopyralid and/or triflusulfuron alone did not adequately control cutleaf eveningprimrose. Triflusulfuron alone effectively controlled wild radish. In the 2013–2014 and 2014–2015 seasons, December-applied POST herbicides did not injure sugarbeet. However, in the 2015–2016 season POST herbicides were applied in late October. On the day of treatment, the maximum temperature was 25.4 C, which exceeded the established upper temperature limit of 22 C for safe application of phenmedipham desmedipham, and sugarbeet plants were severely injured. In the southeastern United States, temperatures frequently exceed 22 C in early autumn, which may limit phenmedipham desmedipham use for controlling troublesome cool-season weeds of sugarbeet in the region. Weed control options need to be expanded to compensate for this limitation.

Nomenclature: Clopyralid; ethofumesate; phenmedipham desmedipham; triflusulfuron; corn spurry, Spergula arvensis L.; cutleaf eveningprimrose, Oenothera laciniata Hill; henbit, Lamium amplexicaule L.; lesser swinecress, Coronopus didymus (L.) Sm.; wild radish, Raphanus raphanistrum L.; sugarbeet, Beta vulgaris L.

Tropical signalgrass (TSG) is one of the most problematic weeds found on golf courses, sports fields, and sod farms in south Florida. The recent ban of monosodium methane-arsonate (MSMA), an organic arsenical herbicide, from urban areas in Florida has left turfgrass managers searching for effective management options. In an effort to avoid relying solely on POST chemical control, this research examined the effect of combining a cultural practice, verticutting, along with PRE and POST herbicides as an integrated weed management approach to controlling TSG in hybrid bermudagrass. Field experiments were conducted at multiple locations over 2 yr in south Florida to: (1) determine whether verticutting before herbicide applications increases TSG control and (2) identify herbicide programs that effectively control TSG. No interactions between verticutting and herbicide programs were detected, but verticutting consistently provided a slight reduction (8% averaged across herbicide treatments) in TSG cover. Treatments containing a PRE herbicide resulted in a significant reduction (20% to 50%) in TSG cover at 52 wk after initial treatment (WAIT), while some POST herbicide treatments reduced TSG cover to <20% at 52 WAIT. A study was conducted to determine which POST herbicide combinations were most efficacious in controlling TSG. Amicarbazone alone provided ≤35% TSG control at 8 and 12 WAIT, but synergistic responses were observed between amicarbazone and mesotrione, trifloxysulfuron, and thiencarbazone foramsulfuron halosulfuron. Two- and three-way combinations of amicarbazone with these POST herbicides resulted in >80% TSG control at 4, 8, and 12 WAIT, with some reaching 100% TSG control at 4 WAIT. Based on these data, verticutting may provide limited complementary control, but certain combinations of POST herbicides exhibited excellent (>95%) TSG control.

Nomenclature: Amicarbazone; foramsulfuron; halosulfuron; mesotrione; monosodium methane-arsonate (MSMA); thiencarbazone; trifloxysulfuron; hybrid bermudagrass, Cynodon dactylon (L.) Pers. X Cynodon transvaalensis Burtt-Davy, cv. ‘Tifway 419’; smallflowered alexandergrass (syn. tropical signalgrass), Urochloa subquadripara (Trin.) R.D. Webster

In a greenhouse experiment, soybean, cotton, corn, grain sorghum, and sunflower were subjected to 1/10 (3 g ai ha^-1), 1/100 (0.3 g ai ha^-1), or 1/500 (0.06 g ai ha^-1) of the 1X rate of florpyrauxifen-benzyl. Visible injury 14 days after treatment (DAT) was the greatest with soybean (96%) when exposed to the highest drift rate of 1/10x or 3 g ai/ha^-1 of florpyrauxifenbenzyl and was significantly higher than all other crops and drift rates. Cotton and sunflower were also injured 85 and 83%, respectively, by the 1/10x rate but had less injury when a 1/100x or 1/500x rate was applied (injury ranging from 9 to 33%). It was concluded that the negative effects on soybean, cotton, and sunflower primarily resulted from exposure to the highest rate tested (1/10x) and only soybean expressed negative effects even at the lower rate of 1/100x. A field study was also conducted to (1) evaluate the sensitivity of soybean to low concentrations of florpyrauxifen-benzyl during vegetative and reproductive development and (2) compare soybean injury and yield following applications of florpyrauxifen-benzyl and dicamba across various growth stages and concentrations. Soybean plants were treated with 1/10, 1/20, 1/40, 1/80, 1/160, 1/320, or 1/640 of the 1X rate of florpyrauxifen-benzyl (30 g ai/ ha^-1) or dicamba (560 g ae ha^-1) at the V3 and R1 growth stage. Florpyrauxifen-benzyl applied at a rate of 1/10 to 1/40X caused foliar injury and subsequent height reduction. In comparison, dicamba applied at the same rates caused slightly less injury and growth reductions. As rate of florpyrauxifen-benzyl decreased from 1/10 to 1/640X, the level of soybean injury dissipated rather quickly. However, this was not the case with dicamba, as substantial injury was observed with rates as low as 1/640X.

Nomenclature: Florpyrauxifen-benzyl; common sunflower, Helianthus annuus L; corn, Zea mays L.; cotton, Gossypium hirsutum L.; sorghum, Sorghum bicolor (L.) Moench ssp. arundinaceum (Desv.) de Wet & Harlan; soybean, Glycine max (L.) Merr

Florpyrauxifen-benzyl is a new synthetic auxin herbicide that will provide a novel site of action in rice production. In many areas of the United States it is common practice to plant soybeans in rotation with rice, thereby introducing the potential for herbicide carryover. Multiple field experiments were conducted in 2014 and repeated in 2015 to evaluate potential plant-back restrictions for soybean and other row crops following an application of florpyrauxifen-benzyl. In the first experiment, treatments comprised florpyrauxifen-benzyl applied at 40 followed by 40 g ai ha^-1, 80 fb 80 g ai ha^-1, and a nontreated check. In 2014, herbicides were applied to a silt loam soil near Stuttgart and Colt, AR, and fields remained fallow following application. The following year, corn, cotton, soybean, grain sorghum, and sunflower were planted within the previously treated area. Stand counts, crop heights, and visual injury assessments were done for each crop following planting, and aboveground biomass data were collected 28 d after planting. No significant differences were observed among the treatments for any of the parameters assessed, highlighting the rotational flexibility of common row crops 1 yr following a florpyrauxifen-benzyl application. In the second experiment, florpyrauxifen-benzyl was applied at 30 and 60 g ai ha^-1 at 56, 28, 14, and 0 d before planting soybean. Injury assessments corresponded to the highest concentration of florpyrauxifen-benzyl and its metabolites recovered from soil at the time of planting. Conversely, soybean injury was reduced when florpyrauxifen-benzyl was applied at increasing intervals before planting. At the end of each season, soybean yield was similar to the nontreated control when florpyrauxifen-benzyl at 30 or 60 g ai ha^-1 was applied 56 d before planting, whereas all other treatments reduced yield. These results support a relatively short replant interval for soybean after florpyrauxifen-benzyl application to rice.

Nomenclature: Florpyrauxifen-benzyl; corn, Zea mays L.; cotton, Gossypium hirsutum L.; grain sorghum, Sorghum bicolor L.; rice, Oryza sativa L.; soybean, Glycine max (L.) Merr.; sunflower, Helianthus annuus L.

A field study was established to study symptoms, growth and yield of 2-year-old walnut trees exposure to simulated drift of several herbicides commonly used in rice production. Bispyribac-sodium, bensulfuron-methyl, and propanil were applied at four rates representing 0.5%, 1%, 3% and 10% of the normal use rate in rice (45, 70, and 6725 g ai ha^-1, for the three herbicides respectively). Symptoms started to appear approximately 7 days after application (DAT) and peaked 28 DAT. At that time, bispyribac-sodium caused greater injury at low drift rates (6% and 15% visual injury for 0.5% and 1% rate, respectively) compared to bensulfuronmethyl and propanil. Bispyribac-sodium also appeared to slow walnut shoot elongation compared to nontreated trees; however, no yield reductions were observed either in the year after drift exposure. The effect of bispyribac-sodium simulated drift on the yield and nut quality in the year of drift exposure was evaluated in a separate study on 3-year-old walnut trees. While no yield or nut quality reductions were observed, a linear correlation between rate of bispyribac-sodium and color, an important quality factor, was found: higher herbicide rates tended to be associated with darker kernel color. Bispyribac-sodium may damage nearby walnut orchards if drifted at significant amounts. However, it is unlikely that in a field situation bispyribac-sodium would drift at high enough levels to cause the symptoms observed from the 10% use rates in this study.

Nomenclature: bispyribac-sodium; bensulfuron-methyl; propanil; rice, Oryza sativa L.; walnut, Juglans regia L.

Enlist E3™ soybean, resistant to 2,4-D, glufosinate, and glyphosate, provides options to control glyphosate-resistant Sumatran fleabane before planting and in crop. Twenty field trials were conducted in Argentina to determine Enlist E3 soybean sensitivity to POST applications of 2,4-D choline glyphosate or glufosinate. Maximum injury from a single 2,4-D choline glyphosate application at 1X (1140 1140 g ae ha^-1) and 2X rate was 4% and 13%, respectively, at 3 days after treatment in the temperate Humid Pampa region. Slightly higher injury of 11 and 23% was observed in sub-tropical region of northern Argentina. Injury was transient with recovery occurring within 14 days. Injury caused by sequential applications was equivalent to that caused by single applications. Soybean yield was not affected by single nor sequential applications. In four trials, control programs containing 2,4-D choline glyphosate applied PRE and POST provided greater GR Sumatran fleabane control and a 12 to 26% increase in yield compared to 2,4-D choline glyphosate applied at PRE only. This research demonstrates the glyphosate-resistant control programs that include 2,4-D choline, glyphosate, and glufosinate provide excellent GR Sumatran fleabane control.

Nomenclature: 2,4-D choline; glufosinate; glyphosate; soybean, Glycine max (L.) Merr; Sumatran fleabane, Conyza sumatrensis (Retz.) E. H. Walker

Control of broadleaf weeds in caladium is difficult due in part to a lack of selective POST herbicides. Cultivation is not an option due to the dense canopy and potential for tuber injury. As a result, growers currently rely on preemergence (PRE) herbicide and hand-weeding. The objective of this research was to evaluate the control of four common broadleaf weeds of field grown caladium with POST applications of halosulfuron, thifensulfuron-methyl, and trifloxysulfuron, and determine the tolerance of caladium cultivars ‘Florida Fantasy’ and ‘Florida cardinal’ to POST applications of halosulfuron. At 4 weeks after treatment (WAT), thifensufluron-methyl at 28 g ai ha^-1 and trifloxysulfuron at 84 g ai ha^-1 provided approximately 90 and 70% common purslane control, respectively, while halosulfuron at 210 g ai ha^-1 provided 55% suppression. Trifloxysulfuron controlled ≥90% spotted spurge at 42 g ha^-1, whereas the highest rate of halosulfuron and thifensulfuron-methyl only achieved 60% suppression. In field experiments, the evaluated sulfonylurea (SU) herbicides were less efficacious on hairy indigo and sharppod morningglory as control never exceeded 65 and 50%, respectively. In greenhouse experiments, the evaluated halosulfuron rates ranging from 26 to 420 g ha^-1 did not significantly reduce caladium tuber weight from the nontreated control. Averaged over halosulfuron rates, ‘Florida Fantasy’ damage was 5 and 6% at 2 and 4 WAT, respectively, while ‘Florida Cardinal’ damage was 11%. We conclude that none of the herbicide treatments effectively controlled all species evaluated. Sequential treatments, higher rates, or tank-mixtures may be necessary to adequately control these species. We also conclude that caladium cultivars ‘Florida Fantasy’ and ‘Florida Cardinal’ have acceptable tolerance to POST applications of halosulfuron. Further research is needed to evaluate caladium tolerance to other SU herbicides.

Nomenclature: Halosulfuron; thifensulfuron-methyl; trifloxysulfuron; common purslane, Portulaca oleracea L.; hairy indigo, Indigofera hirsuta L.; sharppod morningglory, Ipomoea cordatotriloba Dennst.; spotted spurge, Chamaesyce maculata (L.) Small; caladium, Caladium bicolor (Aiton) Vent

Fomesafen provides effective control of glyphosate-resistant Palmer amaranth in cotton. However, cotton seedlings can be injured when fomesafen is applied PRE. Therefore, greenhouse and field experiments were conducted at Athens, GA, and at six locations in Alabama and Georgia in 2013 and 2016 to evaluate cotton growth and yield response to fomesafen applied PRE at 70, 140, 280, 560, 1,120, or 2,240 g ai ha^-1, and in combination with pendimethalin, diuron, acetochlor, and fluridone at 1× label rates. Greenhouse bioassays indicated that fomesafen reduced cotton height and dry weight with increasing rate in Cecil sandy loam and Tifton loamy sand but not in Greenville sandy clay loam--possibly as a result of this soil's higher organic matter (OM) and clay content. Fomesafen applied at 2,240 g ai ha^-1 reduced cotton stand by as much as 83% compared to the nontreated check (NTC) at all field locations except Alabama's Macon and Baldwin counties, and 1,120 g ai ha^-1 reduced cotton stand only at Pulaski County, GA, by 52%. Cotton height was reduced by the two highest rates of fomesafen at all locations except Clarke County, GA, and Baldwin County, AL. Injury data indicated more visual injury followed increasing fomesafen rates, and high-rate treatments produced more injury in sandier soils. Cotton yield was unaffected by herbicide treatments at any location, except for the 1,120 g ai ha^-1 rate at Pulaski County (49% yield loss compared to NTC), 2,240 g ai ha^-1 at Pulaski County (72% yield loss), and Tift County (29% yield loss). These data indicated cotton yield should not be negatively affected by fomesafen applied PRE alone within label rates or in combination with pendimethalin, diuron, acetochlor, and fluridone at 1× label rates, although some visual injury, or stand or height reduction may occur early in the growing season.

Nomenclature: Acetochlor; diuron; fluridone; fomesafen; glyphosate; pendimethalin; Palmer amaranth, Amaranthus palmeri S. Wats.; cotton, Gossypium hirsutum L.

Field studies were conducted to determine watermelon tolerance and yield response when treated with bicyclopyrone preplant (PREPLANT), POST, and POST-directed (POST-DIR). Treatments consisted of two rates of bicyclopyrone (37.5 and 50 g ai ha^-1), fomesafen (175 g ai ha^-1), S-metolachlor (802 g ai ha^-1), and a nontreated check. Preplant treatments were applied to formed beds 1 d prior to transplanting and included bicyclopyrone (37.5 and 50 g ha^-1) and fomesafen (175 g ha^-1), and new polyethylene mulch was subsequently laid above treated beds. POST and POST-DIR treatments were applied 14 ± 1 d after watermelon transplanting and included bicyclopyrone (37.5 and 50 g ha^-1) POST and POST-DIR, and S-metolachlor (802 g ai ha^-1) POST-DIR. POST-DIR treatments were applied to row middles, ensuring that no herbicide contacted watermelon vines or polyethylene mulch. At 2 wk after transplanting (WAT), 15% foliar bleaching was observed in watermelon treated with bicyclopyrone (50 g ha^-1) PRE. At 3 WAT, bicyclopyrone (37.5 and 50 g ha^-1) POST caused 16% and 17% foliar bleaching and 8% and 9% crop stunting, respectively. At 4 WAT, initial injury had subsided and bicyclopyrone (37.5 and 50 g ha^-1) POST caused 4% and 4% foliar bleaching and 4% and 8% crop stunting, respectively. No symptoms of bleaching or stunting were observed at 6- and 8-WAT ratings. Watermelon total yield, marketable yield, total fruit number, marketable fruit number, and average fruit size were unaffected by herbicide treatments. Therefore, registration of bicyclopyrone (37.5 and 50 g ha^-1) PREPLANT, POST, and POST-DIR would offer watermelon producers a safe herbicide option and a novel mode of action for weed management.

Nomenclature: bicyclopyrone, fomesafen, S-metalochlor, watermelon, Citrullus lanatus (Thunb.) Matsum. & Nakai.

Diphenyl ether herbicides are commonly applied POST in soybean to control weeds late in the growing season that have not been controlled by other previous weed management tactics. These “rescue” applications can occur during reproductive soybean growth. The effect of these herbicides on the developing flowers and pods is not known. Field research studies were conducted over 3 yr to determine how soybean flowers and developing pods respond to fomesafen, acifluorfen, and lactofen when applied at R1, R3, and R5 growth stages. Flower and pod counts in the nontreated check showed an increase (17.1, 5.8, and 2.21 at R1, R3, and R5 stage, respectively) and were statistically the same as the herbicide treatments 1 wk after treatment. Fomesafen, acifluorfen, and lactofen applied at 395, 420, and 219 g ai ha^-1 at R1, R3, and R5 stage had no negative impact on soybean flowers and developing pods when compared to the nontreated check. No significant differences were observed in soybean yield between any treatments in all site-years of the study.

Nomenclature: Fomesafen; acifluorfen; lactofen; soybean, Glycine max (L.) Merr.

Plant growth stage and temperature influence the activity of glyphosate on common lambsquarters. A biotype of common lambsquarters in Dickinson County, KS (DK) was not controlled upon treatment with glyphosate in the field. In a greenhouse dose–response study, the DK biotype expressed 1.5-fold less sensitivity to glyphosate compared to a known susceptible biotype from Riley County, KS (RL). Common lambsquarters plants were treated at different growth stages (5 to 7, 10 to 12, 15 to 17, or 19 to 21 cm tall) with glyphosate at a field rate (840 g ae ha^-1), and, regardless of the biotype, plants were more susceptible to glyphosate when they were 5 to 7 cm tall. Common lambsquarters plants were treated with glyphosate (840 g ae ha^-1) after growing at different temperatures (25/15, 32.5/22.5, or 40/30 C day/night), and regardless of the biotype, plants were more susceptible to glyphosate when grown at 25/15 C. The results suggest that the DK biotype exhibits reduced sensitivity to glyphosate compared to the RL biotype, and glyphosate applied at field rate would be more effective on smaller common lambsquarters plants and at cooler temperatures. Common lambsquarters seedlings tend to emerge when temperatures are cooler, early in the spring relative to other summer annual weeds. Therefore, plants should be identified and treated earlier in the growing season for best efficacy with glyphosate.

Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L. CHEAL.

Across the southeastern United States, pyridine carboxylic acid herbicides are widely used for broadleaf weed control in permanent grass pastures. This family of herbicides has proved very successful for controlling most broadleaf weeds commonly present in southeastern pastures and hayfields. In the southern United States, producers have expressed concern when overseeding legume species into warm-season perennial sods following application of commonly used pyridine carboxylic acid herbicides, as legumes are generally highly sensitive to this herbicide family. Field experiments were established to evaluate two herbicide treatment programs (residual vs nonresidual) on crimson clover overseeded into bermudagrass sod. The residual herbicide program included aminopyralid plus 2,4-D (0.09 0.7 kg ae ha^-1), and the nonresidual program included triclopyr plus fluroxypyr (0.63 0.21 kg ae ha^-1) plus 2,4-D (1.12 kg ae ha^-1). Herbicide programs were applied at two key timings: in spring (May) and early summer (June). Spring applications were also evaluated when used in single vs repeated annual application. Our results did not indicate soil residual herbicide issues for crimson clover planted in the fall following spring or early-summer application of aminopyralid 2,4-D at either location. Additionally, there were no cumulative negative impacts on crimson clover following 2 yr of spring herbicide application. Crimson clover cover, however, strongly decreased as grass and weed cover increased—an event that may be related to greater interspecific competition at higher levels of grass and weed cover. Soil fertility, weather, and competition from resident annual grasses and weeds strongly influenced productivity, suggesting that changes in pasture dynamics had a greater influence on clover productivity than did herbicide treatment or timing of application.

Nomenclature: Aminopyralid; fluroxypyr; triclopyr; 2,4-D; bermudagrass, Cynodon dactylon (Pers.) L.; crimson clover, Trifolium incarnatum L

Reforestation in the Inland Northwest, including northeastern Oregon, USA, is often limited by a dry climate and soil moisture availability during the summer months. Reduction of competing vegetative cover in forest plantations is a common method for retaining available soil moisture. Several spring and summer site preparation (applied prior to planting) herbicide treatments were evaluated to determine their efficacy in reducing competing cover, thus retaining soil moisture, on three sites in northeastern Oregon. Results varied by site, year, and season of application. In general, sulfometuron (0.14 kg ai ha^-1 alone and in various mixtures), imazapyr (0.42 ae kg ha^-1), and hexazinone (1.68 kg ai ha^-1) resulted in 3 to 17% cover of forbs and grasses in the first-year when applied in spring. Sulfometuron glyphosate (2.2 kg ha^-1) consistently reduced grasses and forbs for the first year when applied in summer, but forbs recovered in the second year on two of three sites. Aminopyralid (0.12 kg ae ha^-1) sulfometuron applied in summer also led to comparable control of forb cover. In the second year after treatment, forb cover in treated plots was similar to levels in nontreated plots, and some species of forbs had increased relative to nontreated plots. Imazapyr (0.21 and 0.42 kg ha^-1) at either rate, spring or summer 2007, or at lower rate (0.14 kg ha^-1) with glyphosate in summer, provided the best control of shrubs, of which snowberry was the dominant species. Total vegetative cover was similar across all treatments seven and eight years after application, and differences in vegetation were related to site rather than treatment. In the first year after treatment, rates of soil moisture depletion in the 0- to 23-cm depth were correlated with vegetative cover, particularly late season soil moisture, suggesting increased water availability for tree seedling growth.

Nomenclature: aminopyralid; glyphosate; hexazinone; imazapyr; sulfometuron; common snowberry, Symphoricarpos albus (L.) S. F. Blake.

Abstract Herbicide resistance is ‘wicked’ in nature; therefore, results of the many educational efforts to encourage diversification of weed control practices in the United States have been mixed. It is clear that we do not sufficiently understand the totality of the grassroots obstacles, concerns, challenges, and specific solutions needed for varied crop production systems. Weed management issues and solutions vary with such variables as management styles, regions, cropping systems, and available or affordable technologies. Therefore, to help the weed science community better understand the needs and ideas of those directly dealing with herbicide resistance, seven half-day regional listening sessions were held across the United States between December 2016 and April 2017 with groups of diverse stakeholders on the issues and potential solutions for herbicide resistance management. The major goals of the sessions were to gain an understanding of stakeholders and their goals and concerns related to herbicide resistance management, to become familiar with regional differences, and to identify decision maker needs to address herbicide resistance. The messages shared by listening-session participants could be summarized by six themes: we need new herbicides; there is no need for more regulation; there is a need for more education, especially for others who were not present; diversity is hard; the agricultural economy makes it difficult to make changes; and we are aware of herbicide resistance but are managing it. The authors concluded that more work is needed to bring a community-wide, interdisciplinary approach to understanding the complexity of managing weeds within the context of the whole farm operation and for communicating the need to address herbicide resistance.

Seven half-day regional listening sessions were held between December 2016 and April 2017 with groups of diverse stakeholders on the issues and potential solutions for herbicideresistance management. The objective of the listening sessions was to connect with stakeholders and hear their challenges and recommendations for addressing herbicide resistance. The coordinating team hired Strategic Conservation Solutions, LLC, to facilitate all the sessions. They and the coordinating team used in-person meetings, teleconferences, and email to communicate and coordinate the activities leading up to each regional listening session. The agenda was the same across all sessions and included small-group discussions followed by reporting to the full group for discussion. The planning process was the same across all the sessions, although the selection of venue, time of day, and stakeholder participants differed to accommodate the differences among regions. The listening-session format required a great deal of work and flexibility on the part of the coordinating team and regional coordinators. Overall, the participant evaluations from the sessions were positive, with participants expressing appreciation that they were asked for their thoughts on the subject of herbicide resistance. This paper details the methods and processes used to conduct these regional listening sessions and provides an assessment of the strengths and limitations of those processes.

Weed control in vegetable production is especially challenging, because few registered herbicides simultaneously offer excellent crop tolerance and broad-spectrum weed control. We report here the response of several vegetables and weeds to 37.5 and 50 g ai ha^-1 of the new herbicide bicyclopyrone (BCP). Vegetable crops showed good tolerance to BCP PRE and post-directed (POST-DIR) in high organic matter content muck soil. POST BCP severely injured all crops. Soil type and the rate of BCP PRE significantly affected response of vegetable crops, and variety of onion was significant. POST BCP controlled hairy galinsoga and small common purslane plants (>80% injury). Hairy galinsoga was not controlled by BCP PRE application in muck soil but was controlled in a 2:3 (vol/vol) blend of Wooster silt loam and a commercial potting mix. Common purslane was slightly injured in the muck soil and was well controlled in the soil and potting mix blend by PRE BCP. The herbicide did not control prostrate pigweed in either soil type or at any growth stage.

Nomenclature: Bicyclopyrone; common purslane, Portulaca oleracea L.; hairy galinsoga, Galinsoga quadriradiata Cav.; prostrate pigweed, Amaranthus blitoides S. Wats.; onion, Allium cepa L.