A meta-analysis of 11 previously published field studies was conducted with the objectives being to (1) estimate the no observable effects dose (NOED) for dicamba on susceptible soybean; (2) evaluate available evidence for hormesis, or increased soybean yield in response to low doses of dicamba; (3) estimate the dose of dicamba likely to cause measurable soybean yield loss under field conditions; and (4) quantify the relationship between visible injury symptoms and soybean yield loss. All studies that included visible injury data (N=7) reported injury symptoms at the lowest nonzero dicamba dose applied (as low as 0.03 g ae ha^-1), and therefore a NOED could not be estimated from the existing peerreviewed literature. Based on statistical tests for hormesis, there is insufficient evidence to support any claim of increased soybean yield at low dicamba doses. Future research should include a range of dicamba doses lower than 0.03 g ha^-1 to estimate a NOED and determine whether a hormesis effect is possible at or below dicamba doses that cause visible injury symptoms. Soybean is more susceptible to dicamba when exposed at flowering (R1 to R2 stage) compared with vegetative stages (V1 to V7). A dicamba dose of 0.9 g ha^-1 (95% CI=0.08 to 1.7) at the flowering stage was estimated to cause 5% soybean yield loss. When exposed at vegetative stages, dicamba doses that cause less than 30% visible injury symptoms (95% CI=23 to 49%) appear unlikely to cause greater than 5% soybean yield loss; however, if soybean is exposed at flowering, visible injury symptoms greater than 12% (95% CI=8 to 16%) are likely to be associated with at least 5% soybean yield loss.

Nomenclature: Dicamba; soybean, Glycine max (L.) Merr.

Introduction of the Roundup Ready® Xtend system (Monsanto Co., St. Louis, MO) provides an alternative weed management option for growers, but of concern is the risk of dicamba injury to sensitive crops, particularly soybean from off-target movement and tank contamination. Experiments were conducted to determine the response of soybean to low rates of dicamba over a wide range of application timings. Two glufosinate-resistant varieties (HBK 4950LL–indeterminate and HALO 5.45LL–determinate) commonly grown in Arkansas were chosen for these studies. Two rates of dicamba, 2.18 and 8.75 g ae ha^-1 (1/256 × and 1/ 64 × of the POST labeled rate for dicamba-resistant soybean), were applied at two vegetative (V4, V6) and six reproductive (R1 to R6) growth stages. Compared to the nontreated control, dicamba applied during late vegetative and early reproductive growth of soybean caused leaf injury, plant height reduction, and seed yield loss for both soybean cultivars. Averaged across dicamba rates applied at R1, soybean seed yield was reduced 14% for the HBK 4950LL cultivar and 19% for the HALO 5.45LL cultivar. Averaged over rates, dicamba applied at R1 to the HALO 5.45LL and HBK 4950LL soybean resulted in 48% and 43% visible injury 4 wk after treatment, respectively. Grain yield was similar to that of the nontreated control when dicamba was applied at the later reproductive stages averaged across rates.

Nomenclature: Glufosinate; dicamba; soybean, Glycine max (L.) Merr

Each year there are multiple reports of drift occurrences, and the majority of drift complaints in rice are from imazethapyr or glyphosate. In 2014 and 2015, multiple field experiments were conducted near Stuttgart, AR, and near Lonoke, AR, to evaluate whether insecticide seed treatments would reduce injury from glyphosate or imazethapyr drift or decrease the recovery time following exposure to a low rate of these herbicides. Study I was referred to as the “seed treatment study,” and Study II was the “drift timing study.” In the seed treatment study the conventional rice cultivar ‘Roy J' was planted, and herbicide treatments included imazethapyr at 10.5 g ai ha^-1, glyphosate at 126 g aeha^-1, or no herbicide. Each plot had either a seed treatment of thiamethoxam, clothianidin, chlorantraniliprole, or no insecticide seed treatment. The herbicides were applied at the two- to three-leaf growth stage. Crop injurywas assessed 1, 3, and 5 wkafter application. Averaged over site-years, thiamethoxam-treated rice had less injury than rice with no insecticide seed treatment at each rating, along with an increased yield. Clothianidintreated rice had an increased yield over no insecticide seed treatment, but the reduction in injury for both herbicides was less pronounced than in the thiamethoxam-treated plots. Overall, chlorantraniliprole was generally the least effective of the three insecticides in reducing injury from either herbicide and in protecting rice yield potential. A second experiment conducted at Stuttgart, AR, was meant to determine whether damage to rice from glyphosate and imazethapyr was influenced by the timing (15, 30, and 45 d after planting) of exposure to herbicides for thiamethoxam-treated and nontreated rice. There was an overall reduction in injury with the use of thiamethoxam, but the reduction in injury was not dependent on the timing of the drift event. Reduction in damage fromphysical drift of glyphosate and imazethapyr as well as increased yields over the absence of an insecticide seed treatment appear to be an added benefit.

Nomenclature: Clothianidin; chlorantraniliprole; glyphosate; imazethapyr; thiamethoxam; rice, Oryza sativa L.

Glyphosate-resistant (GR) Italian ryegrass is one of the most troublesome weeds in Mississippi row crop production. Fall-applied residual herbicide applications are recommended for control of GR Italian ryegrass. However, carryover of residual herbicides applied in fields for rice production can have a negative impact on rice performance. Field studies were conducted in Stoneville, MS, to determine the effects of fall-applied residual herbicides on rice growth and yield. Herbicide treatments included suggested use rates (1 × ) of clomazone at 840 g ai ha^-1, pyroxasulfone 170 g ai ha^-1, S-metolachlor 1,420 g ai ha^-1, and trifluralin 1,680 g ai ha^-1, and two times (2 × ) the suggested use rates in the fall before rice seeding. Pooled across application rate, pyroxasulfone, S-metolachlor, and trifluralin injured rice to an extent 28% to 36% greater than clomazone 14 d after emergence (DAE). Rice seedling density and height 14 DAE and rice maturity were negatively affected by all fallapplied herbicides except clomazone. Applications at 2 × rates reduced rough rice yields in plots treated with pyroxasulfone, S-metolachlor, and trifluralin compared with clomazone. Pyroxasulfone applied at the 2 × rate reduced rough rice yield 22% compared with the 1 × rate. Rough rice yield was 90% or greater of the nontreated control in plots treated with either rate of S-metolachlor, and these were comparable with rough rice yields from plots treated with both rates of trifluralin and the 1 × rate of pyroxasulfone. Early-season injury and reductions in seedling density and height 14 DAE, would preclude even 1 × applications of pyroxasulfone, S-metolachlor, and trifluralin from being viable options for residual herbicide treatments targeting GR Italian ryegrass in the fall before rice seeding. Of the herbicides evaluated, only clomazone should be utilized as a fall-applied residual herbicide treatment targeting GR Italian ryegrass before seeding rice.

Nomenclature: Clomazone; S-metolachlor; trifluralin; pyroxasulfone; rice, Oryza sativa L.; Italian ryegrass, Lolium perenne ssp. multiflorum (Lam.) Husn

Two field studies were conducted in Louisiana to determine the impact of Nealley's sprangletop on rough rice yield under multiple environments in 2014, 2015, and 2016. The first study evaluated optimal timings of Nealley's sprangletop removal for optimizing rough rice yields. The second study evaluated the impact of Nealley's sprangletop densities on rough rice yield. Nealley's sprangletop was removed with applications of fenoxaprop at 122 g ai ha^-1 at 7, 14, 21, 28, 35, and 42 d after emergence (DAE). Nealley's sprangletop removal at 7 and 14 DAE resulted in higher rough rice yields of 7,880 and 6,960 kg ha^-1, respectively, when compared with the rice from the season-long Nealley's sprangletop competition with a 6,040 kg ha^-1 yield. Delaying herbicide application from 7 DAE to 42 DAE resulted in a yield loss of 1,740 kg ha^-1. Over the 35-d delay in application, rough rice yield loss from Nealley's sprangletop interference was equivalent to 50 kg ha^-1 d^-1. Nealley's sprangletop densities were established at 1, 3, 7, 13, and 26 plants m^-2 by transplanting Nealley's sprangletop when rice reached the one- to two-leaf stage. At Nealley's sprangletop densities of 1 to 26 plants m^-2, rough rice yields were reduced 10 to 270 kg ha^-1, compared with the rice from weed-free plots. Based on regression analysis, Nealley's sprangletop densities of 1, 35, 70, and 450 plants m^-2 reduced rough rice yield 0.14%, 5%, 10%, and 50%, respectively.

Nomenclature: Fenoxaprop; Nealley's sprangletop, Leptochloa nealleyi Vasey; rice, Oryza sativa L.

The evolution of herbicide resistance is making it extremely difficult for US rice producers to use chemical control on weed species such as barnyardgrass and red rice. To combat herbicide resistance, it is imperative that alternative herbicide sites of action (SOAs) be incorporated into rice whenever possible. There are currently no very-long-chain fatty acid– inhibiting herbicides (WSSA Group 15) labeled for use in US rice; however, pethoxamid is one such herbicide currently under development. If appropriate rice tolerance and weed control can be established, pethoxamid would represent a unique herbicide SOA for use in US rice. We conducted field trials near Stuttgart, AR, in 2015 and near Colt and Lonoke, AR, in 2016 to assess selectivity of pethoxamid and weed control alone and in combination with other herbicides as a delayed preemergence (DPRE) application in drill-seeded rice. Pethoxamid was applied at 0, 420, or 560 g ai ha^-1 alone and in combination with clomazone, imazethapyr, pendimethalin, and quinclorac. Minimal rice injury occurred with any treatment assessed. A reduction in rice shoot density and plant height compared to the nontreated control followed the use of pethoxamid; however, no decrease in yield resulted. The highest levels of barnyardgrass control followed the use of imazethapyr at 91% and quinclorac at 89% regardless of the presence of pethoxamid near Lonoke; however, pethoxamid applied at both rates in combination with clomazone and quinclorac increased barnyardgrass control compared to clomazone and quinclorac applied alone. Near Colt, barnyardgrass control of 92% and 96% resulted from pethoxamid alone, averaged over the high and low rates. Based on these data, rice can tolerate pethoxamid when applied DPRE, and adequate levels of barnyardgrass control can be achieved at the rates evaluated within a program; hence, pethoxamid appears to be a viable option for use in rice to allow for increased rotation of herbicide SOAs to combat herbicide-resistant and difficult-tocontrol weeds.

Nomenclature: Pethoxamid; barnyardgrass, Echinochloa crus-galli (L.) Beauv.; red rice, Oryza spp..; rice, Oryza sativa L.

Herbicide resistance to several of the most common weed species in US rice production, such as barnyardgrass and red rice, has made weed control extremely difficult with available herbicide options. No very-long-chain fatty acid–inhibiting herbicides are labeled for use in US rice; however, pethoxamid is one such herbicide under development for soil-applied use to control grasses and small-seeded broadleaves in rice and various row crops. Field trials were conducted in 2015 and 2016 near Stuttgart, AR, for rice tolerance and in 2016 near Colt, AR, and Lonoke, AR, for weed control with the use of pethoxamid-containing rice herbicide programs. Pethoxamid was applied alone and in a program at 420 and 560 g ai ha^-1 with other herbicides labeled in rice including clomazone, quinclorac, propanil, imazethapyr, and carfentrazone POST. Injury less than 10% was seen for all treatments 2 wk after application in 2015 and 2016, except for pethoxamid at 420 g ha^-1 to clomazone to one-leaf rice. Rice injury dissipated to less than 5% following all treatments by 4 wk after flood establishment. Barnyardgrass was controlled 95% or more near Colt and 93% or more near Lonoke for herbicide programs including clomazone PRE followed by pethoxamid plus quinclorac or imazethapyr at three- to four-leaf stage rice. Considering the minimal injury and high levels of barnyardgrass control associated with pethoxamid-containing weed control programs, pethoxamid provides a unique and effective site of action for use in US rice production.

Nomenclature: Carfentrazone; clomazone; imazethapyr; pethoxamid; propanil; quinclorac; barnyardgrass, Echinochloa crus-galli (L.) Beauv.; red rice, Oryza sativa var. sylvatica L.; rice, Oryza sativa L

Recent advances in biotechnology have resulted in crops that are tolerant to the synthetic auxin 2,4-D, expanding the weed management versatility of this herbicide. With potential expansions of use, concerns have been raised about the increased risk of herbicide drift, leading to damage to nontarget crops. A field-scale study was conducted with the objective to measure drift deposition and the potential for drift reduction conferred by a proprietary premixture formulation of 2,4-D choline salt plus glyphosate dimethylammonium salt compared to an in-tank mixture of 2,4-D dimethylamine salt plus glyphosate potassium salt. Treatments were made with field-scale spray equipment under typical application conditions in McCook, NE, using three widely used nozzle tips. Deposition was captured in triplicate downwind collector lines and assayed for tracer dye and 2,4-D. In comparison to the in-tank mixture, the pre-mixture formulation exhibited lower downwind depositions when applied through a flatfan (TeeJet Extended Range; XR) and air induction (TeeJet Air Induction Extended Range; AIXR) nozzles, but not with a pre-orifice (TeeJet TurboTeeJet Induction; TTI) nozzle. Based upon median deposition at 30m downwind, the pre-mixture formulation reduced drift by 62% and 91%, for the XR and AIXR nozzles, respectively. From a drift reduction perspective, the pre-mixture formulation performance with the AIXR nozzle was equivalent to a much coarser TTI nozzle while still offering sufficient foliar coverage for acceptable weed control.

Nomenclature: 2,4-D; glyphosate

2,4-dimethylamine salt (2,4-D) is a synthetic auxin herbicide used extensively in turfgrass for selective broadleaf weed control. Previous research has shown that 2,4-D can dislodge from treated turf, notably in the presence of canopy moisture. Practitioners commonly apply 2,4-D in combination with various commercially available surfactants to increase efficacy. Field research was completed to evaluate the effect of surfactant inclusion and sample collection time within a day on dislodgeable 2,4-D residue from perennial ryegrass. Research was initiated May 24, 2016 in Raleigh, NC and repeated in time to quantify dislodgeable 2,4-D following application (2.1 kg ae ha^-1) either alone or with a nonionic surfactant (0.5% vol/vol). Sample collection occurred 1, 2, 3, 6, 12 or 24 d after treatment (DAT) at AM [7:00 AM Eastern Standard Time (EST)] andPM(2:00PMEST) sample timings within a day. 2,4-D applied with surfactant (0.4% to 25.4% of applied) reduced dislodgeable foliar residue compared to 2,4-D applied alone (0.5% to 31.2%) from 1 through 6 DAT, whereas dislodgeable 2,4-D was not detected at 12 and 24 DAT. Regardless of surfactant inclusion or absence, samples collected in theAMresulted in a 5- to 10-fold increase in dislodgeable 2,4-D compared to samples collected in the PM from 1 through 6 DAT, suggesting that 2,4-D dislodgeability may be influenced by conditions favoring canopy moisture development. This research will improve turfgrass management practices and research designed to minimize human 2,4-D exposure.

Nomenclature: 2,4-D; perennial ryegrass, Lolium perenne L.

Field bindweed, a member of the Convolvulaceae family, is a problematic perennial weed in cotton fields and orchards in northwest China. The species exhibits strong seed dormancy, causing delayed germination. A clear understanding of the mechanisms involved in alleviating seed dormancy is important for effective plant propagation and successful management of field bindweed. Experiments were conducted to investigate seed germination and radicle growth of field bindweed by breaking seed dormancy using mechanical scarification, sulfuric acid, hot-water scarification, cold stratification, and chemical treatment. Chemical treatments (gibberellic acid or potassium nitrate) had no effect on breaking seed dormancy, whereas mechanical scarification (sandpaper and blade) resulted in 92% to 98% seed germination, indicating that seed dormancy of field bindweed was mainly due to the presence of a hard seed coat. Seeds pretreated with 80% sulfuric acid for 15 to 60 min or 98% sulfuric acid for 15 to 30 min had germination rates above 80%, and soaking seeds in 70 C water for 4 to 16 min or in boiling water for 5 to 20 s were effective in breaking seed dormancy but had no effect on the radicle growth of field bindweed. Cold stratification at 5 C for 2 to 8 wk partially accelerated seed dormancy release, resulting in 53% to 67% seed germination. Results indicated that field bindweed could potentially form a persistent soil seed bank with physically dormant seed; therefore, strategies for eliminating seed production should be adopted.

Nomenclature: Field bindweed; Convolvulus arvensis L.

Field experiments were performed in 2016 and 2017 in Missouri to determine whether interactions exist between PRE herbicides and seed treatments in soybean. The experiments consisted of a randomized complete block design with factorial arrangements of varieties, seed treatments, and herbicides. We selected two genetically similar varieties of soybean, one with known tolerance to PPO-inhibiting herbicides and one with known sensitivity. Each variety of seed received three separate seed treatment mixtures (STMs): (1) STM1, imidacloprid plus prothioconazol + penflufen +metalaxyl plus metalaxyl plus Bacillus subtilis + B. pumilis, (2) STM2, Pasteuria nishizawae plus thiamethoxam plus prothioconazol + penflufen +metalaxyl plus metalaxyl plus B. subtilis + B. pumilis, and (3) STM3, fluopyram plus imidacloprid plus prothioconazol + penflufen +metalaxyl plus metalaxyl plus B. subtilis + B. pumilis. Chlorimuron-ethyl + flumioxazin + pyroxasulfone, chlorimuron-ethyl + flumioxazin +metribuzin, and chlorimuron-ethyl + sulfentrazone were applied PRE to each variety and seed treatment combination at 1× and 2× the labeled use rate. Chlorimuron-ethyl + sulfentrazone treatment at the 2 × rate resulted in greater injury of 8% and 14% to the sensitive variety than the tolerant in 2016 and 2017, respectively; this was the highest injury observed from any herbicide treatment in either year. In 2017, chlorimuron-ethyl + sulfentrazone resulted in the greatest height reductions in both varieties, but this reduction was more evident in the sensitive (19%) than in the tolerant (6%) variety. Overall, yield differences between the two varieties were not consistent between years, and for both varieties, the sulfentrazonecontaining treatments resulted in the highest yield losses. The results of this research indicate that there is a larger interaction between herbicides and varieties than there is between herbicides and seed treatments, or seed treatments and varieties.

Nomenclature: Chlorimuron-ethyl; flumioxazin; fluopyram; imidacloprid; metalaxyl; metribuzin; Pasteuria nishizawae; penflufen; prothioconazol; pyroxasulfone; sulfentrazone; thiamethoxam; soybean, Glycine max (L.) Merr

We conducted a greenhouse study to evaluate the differential response of Palmer amaranth to glyphosate and mesotrione and to quantify the level of tolerance to mesotrione in recalcitrant (difficult-to-control) accessions and their offspring. Seeds were collected from 174 crop fields (corn, cotton, and soybean) across Arkansas between 2008 and 2016. Palmer amaranth seedlings (7 to 10cm tall) were treated with glyphosate at 840 g ae ha^-1 or mesotrione at 105 g ha^-1. Overall, 47% of the accessions (172) were resistant to glyphosate with 68% survivors. Almost 35% of accessions were highly resistant, with 90% survivors. The majority of survivors from glyphosate application incurred between 31% and 60% injury. Mesotrione killed 66% of the accessions (174); the remaining accessions had survivors with injury ranging from 61% to 90%. Accessions with the least response to mesotrione were selected to determine tolerance level. Dose–response assays were conducted with four recalcitrant populations and their F₁ progeny. The average effective doses (ED₅₀) for the parent accessions and F₁ progeny of survivors were 21.5 g ha^-1 and 27.5 g ha^-1, respectively. The recalcitrant parent populations were three- to five-fold more tolerant to mesotrione than the known susceptible population, as were the F₁ progeny.

Nomenclature: glyphosate; mesotrione; Palmer amaranth, Amaranthus palmeri S. Wats.; corn, Zea mays L.; cotton, Gossypium hirsutum L.; soybean, Glycine max (L.) Merr.

Field studies were conducted in North Carolina to determine the critical period for Palmer amaranth control (CPPAC) in pickling cucumber. In removal treatments (REM), emerged Palmer amaranth were allowed to compete with cucumber for 14, 21, 28, or 35 d after sowing (DAS) in 2014 and 14, 21, 35, or 42 DAS in 2015, and cucumber was kept weed-free for the remainder of the season. In the establishment treatments (EST), cucumber was maintained free of Palmer amaranth by hand removal until 14, 21, 28, or 35 DAS in 2014 and until 14, 21, 35, or 42 DAS in 2015; after this, Palmer amaranth was allowed to establish and compete with the cucumber for the remainder of the season. The beginning and end of the CPPAC, based on 5% loss of marketable yield, was determined by fitting log-logistic and Gompertz equations to the relative yield data representing REM and EST, respectively. Season-long competition by Palmer amaranth reduced pickling cucumber yield by 45% to 98% and 88% to 98% during 2014 and 2015, respectively. When cucumber was planted on April 25, 2015, the CPPAC ranged from 570 to 1,002 heat units (HU), which corresponded to 32 to 49 DAS. However, when cucumber planting was delayed 2 to 4 wk (May 7 and May 21, 2014 and May 4, 2015), the CPPAC lasted from 100 to 918 HU (7 to 44 DAS). This research suggested that planting pickling cucumber as early as possible during the season may help to reduce competition by Palmer amaranth and delay the beginning of the CPPAC.

Nomenclature: Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; cucumber, Cucumis sativus L.

Protoporphyrinogen IX oxidase (PPO)–inhibiting herbicides (WSSA Group 14) have been used in agronomic row crops for over 50 yr. Broadleaf weeds, including glyphosate-resistant Palmer amaranth, have been controlled by this herbicide site of action PRE and POST. Recently, Palmer amaranth populations were reported resistant to PPO inhibitors in 2011 in Arkansas, in 2015 in Tennessee, and in 2016 in Illinois. Historically, the mechanism for this resistance involves the deletion of a glycine at position 210 (ΔG210) in a PPO enzyme encoded by the PPX2 gene; however, the ΔG210 deletion did not explain all PPO inhibitor–resistant Palmer amaranth in Tennessee populations. Recently, two new mutations within PPX2 (R128G, R128M) that confer resistance to PPO inhibitors were identified in Palmer amaranth. Therefore, research is needed to document the presence and distribution of the three known mutations that confer PPO inhibitor resistance in Tennessee. In 2017, a survey was conducted in 18 fields with Palmer amaranth to determine whether resistance existed and the prevalence of each known mutation in each field. Fomesafen was applied at 265 g ai ha^-1 to Palmer amaranth infestations within each field to select for resistant weeds for later analysis. Where resistance was described (70% of surviving plants), the ΔG210 mutation was detected in 47% of resistant plants. The R128G mutation accounted for 42% of resistance, similar to the frequency of the ΔG210 mutation. The R128M mutation was less frequent than the other two mutations, accounting for only 10% of the resistance. All mutations detected in this study were heterozygous. Additionally, no more than one of the three PPX2 mutations were detected in an individual surviving plant. Similar to previous research, about 70% of PPO resistance was accounted for by these three known mutations, leaving about 30% of resistance not characterized in Tennessee populations. Survivors not showing the three known PPO mutations suggest that other resistance mechanisms are present.

Nomenclature: fomesafen; Palmer amaranth, Amaranthus palmeri S. Wats.

Synthetic auxin herbicides such as 2,4-D and dicamba are often utilized to control broadleaf weeds in preplant burndown applications to soybean. Halauxifen-methyl is a new synthetic auxin herbicide for broadleaf weed control in preplant burndown applications to corn, cotton, and soybean at low use rates (5 g ae ha^-1). Field experiments were conducted to evaluate efficacy and weed control spectrum of halauxifen-methyl applied alone and in mixtures with 2,4-D (560 g ae ha^-1), dicamba (280 g ae ha^-1), and glyphosate (560 g ae ha^-1). Glyphosate-resistant (GR) horseweed was controlled with halauxifen-methyl applied alone (90% control) and in mixtures (87% to 97% control) 35 d after treatment (DAT). Common ragweed was controlled 93% with halauxifen-methyl applied alone and 91% to 97% in mixtures 35 DAT. Halauxifenmethyl applied alone resulted in poor giant ragweed control 21 DAT (73% control); however, mixtures of halauxifen-methyl with 2,4-D, dicamba, or glyphosate controlled giant ragweed (86% to 98% control). Halauxifen-methyl alone resulted in poor redroot pigweed control (62% control) 21 DAT; however, mixtures of halauxifen-methyl with dicamba, 2,4-D, or glyphosate controlled redroot pigweed (89% to 98% control). Halauxifen-methyl controls GR horseweed and common ragweed applied alone and in mixtures with other synthetic auxin herbicides and glyphosate. Furthermore, mixing 2,4-D or dicamba with halauxifen-methyl can increase the weed control spectrum in preplant burndown applications.

Nomenclature: 2,4-D; dicamba; glyphosate; halauxifenmethyl; common ragweed, Ambrosia artemisiifolia L. AMBEL; giant ragweed, Ambrosia trifida L. AMBTR; horseweed, Conyza canadensis (L.) Cronq. ERICA; redroot pigweed, Amaranthus retroflexus L. AMARE; corn, Zea mays L.; cotton, Gossypium hirsutum L.; soybean, Glycine max (L.) Merr

A glasshouse study was established at Louisiana State University campus in Baton Rouge, LA, to evaluate the control of fall panicum and Nealley's sprangletop treated with florpyrauxifen-benzyl. Florpyrauxifen was applied at 30 g ai ha^-1 to each grass species at the three- to four-leaf and oneto two-tiller stages of growth. At 21 d after treatment (DAT), fall panicum control was 91% when treated with florpyrauxifen at the three- to four-leaf stage, and Nealley's sprangletop control was 78% to 82%, regardless of application timing 21 DAT. Leaf number, tiller number, plant height, and plant fresh weight were reduced when fall panicum and Nealley's sprangletop were treated with florpyrauxifen. This information can be useful for developing weed management strategies with this herbicide for rice production, and it provides an additional mode of action to help manage and/or delay the development of herbicide-resistant weeds.

Nomenclature: Florpyrauxifen-benzyl [benzyl-4-amino-3- chloro-6-(4-chloro-2-fluoro-3-methoxyphenyl)- 5-fluoropyridine-2-carboxylate]; fall panicum, Panicum dichotomiflorum Michx.; Nealley's sprangletop, Leptochloa nealleyi Vasey; rice, Oryza sativa L.

Research conducted in the field identified 14 injury criteria associated with dicamba (Clarity® diglycolamine salt) applied at 0.6 to 280 g ae ha^-1 (1/1,000 to 1/2 of 560 g ha^-1 use rate) to indeterminate soybean at V3/V4 or R1/R2. For each criterion, injury was rated using a scale of 0=no injury, 1=slight, 2= slight to moderate, 3=moderate, 4=moderate to severe, and 5=severe. Greatest crop injury 15 d after treatment (DAT) was observed for dicamba rates of 0.6 to 4.4 g ha^-1 for upper canopy pale leaf margins (3.8 to 4.2) at V3/V4 and for terminal leaf cupping (4.1 to 5.0) at R1/R2, and for rates of 0.6 to 8.8 g ha^-1 for upper canopy leaf cupping (3.8 to 4.8) and upper canopy leaf surface crinkling (3.4 to 4.4) at V3/V4. Injury 15 DAT was equivalent to the nontreated control for dicamba rates as high as 4.4 g ha^-1 for lower stem base swelling at V3/V4 and for upper canopy leaf rollover/inversion and terminal leaf necrosis at R1/R2; for rates as high as 8.8 g ha^-1 for leaf petiole base swelling and stem epinasty at R1/ R2, and lower stem base lesions/cracking (V3/V4 and R1/R2 average); and for rates as high as 17.5 g ha^-1 for lower leaf soil contact at V3/V4 and leaf petiole droop at R1/R2. The response to increasing dicamba rate observed for the injury criteria was in contrast to the steady increase in visual injury and plant height reduction rated as 0 to 100%. The moderate to severe upper canopy leaf cupping, pale leaf margins, and leaf surface crinkling, and terminal leaf cupping 15 DAT with dicamba at 0.6 to 4.4 g ha^-1 corresponded to soybean yield loss of 1% to 9% for application at V3/V4 and 2% to 17% at R1/R2.

Nomenclature: Dicamba; soybean, Glycine max (L.) Merr

A field study was established to evaluate symptoms, growth, yield, and nut quality of walnut trees subjected to multiple exposures of simulated bispyribac-sodium drift. Nut yield the year following simulated drift treatment was also evaluated because tissue differentiation for future fruiting position occurs in the prior season. Bispyribac-sodium was applied four times, at weekly intervals, at 0.5% and 3% of the use rate in rice (45 g ai ha^-1). Injury from the 0.5% rate exceeded 5% after three applications. In general, the severity of the symptoms peaked 14 d after last application (23% and 40% injury for 0.5% and 3% rate, respectively) and subsequently remained nearly constant over the duration of the study. Growth of shoots treated with the 0.5% rate was initially delayed during the treatment regime but recovered after treatments ended; however, walnut shoots exposed to the higher rate had fewer internodes than nontreated trees at the end of the season. No measurable reduction in walnut yield or average nut weight either in the year of exposure or in the subsequent year was observed. However, both rates negatively affected walnut kernel color in the year of exposure.

Nomenclature: Bispyribac-sodium; rice, Oryza sativa L.; walnut, Juglans regia L.

A 3-yr watermelon experiment was established in fall 2013 to evaluate cover crop, polyethylene mulch, tillage, and herbicide application components for weed control, yield, and profitability. Conservation tillage, either with a cereal rye cover crop alone or integrated with polyethylene mulch, was compared to the standard industry practice of conventional tillage with bedded polyethylene mulch. The study also used a non-bedded conventional tillage system without polyethylene to determine polyethylene and cover crop residue effects. Within each of the four systems, herbicide treatments comprised halosulfuron applied (1) at 26.3 g ai ha^-1 PRE, (2) at 26.3 g ai ha^-1 POST, or (3) sequentially at 26.3 g ai ha^-1 PRE and POST. Each system also had a nontreated control. In addition, clethodim was applied in all plots twice POST at 140 g ai ha^-1, except for nontreated in each system. In 2014, polyethylene or cereal rye cover crop effectively controlled tall morningglory, coffee senna, and carpetweed early season in nontreated plots, whereas the integration of the two was effective at controlling common purslane. Tall morningglory and purslane control was insufficient late season regardless of production system and herbicide application. In 2015, polyethylene effectively controlled cutleaf eveningprimrose, sicklepod, and arrowleaf sida early season in nontreated plots. Yellow nutsedge control was insufficient late season regardless of production system and herbicide application. Utilizing sequential halosulfuron applications did not increase weed control over PRE or POST alone in all years. Polyethylene use resulted in yields higher than systems without in all years. Across all 3 yr, net returns were highest for polyethylene mulch systems. The results of this experiment underscore the need for more progress in developing integrated conservation systems for watermelon production. Effective herbicides, low-disturbance cultivation, and/or hand weeding are most likely the key to success in conservation specialty crop systems.

Nomenclature: Clethodim; halosulfuron; arrowleaf sida, Sida rhombifolia L.; cereal rye, Secale cerale L.; carpetweed, Mollugo verticillata L.; coffee senna, Senna occidentalis (L.) Link; common purslane, Portulaca oleracea L.; cutleaf eveningprimrose, Oenothera laciniata Hill; large crabgrass, Digitaria sanguinalis (L.) Scop.; sicklepod, Senna obtusifolia (L.) H.S. Irwin & Barneby; yellow nutsedge, Cyperus rotundus L.; tall morningglory, Ipomoea purpurea (L.) Roth; watermelon, Citrullus lanatus (Thunb.) Matsum. & Nakai

Economically solvent fresh-market potato production is predominantly dependent on the ability to efficiently produce consistent tuber quality and high yield, and the ability to meet first-to-market demand with early-season potatoes. Unfortunately, these two qualifiers often work against each other in terms of production management. In response, we studied integrated potato vine management programs that support timely early-season potato harvest. Vine management with a flail chopper, roller, and flame burner used alone or followed by diquat was evaluated when initiated 21 or 14 d prior to harvest in 2015 and 2016. Potato varieties included ‘Yukon Gold' and ‘Dark Red Norland'. Potato leaf and stem management, as well as tuber skinning, stolon separation, grade, and yield were quantified. Among mechanical methods, potato leaf and stem management were poor when vines were rolled or mowed but better when flail chopped. In general, vine management and tuber skin set was better when treatments were initiated 21 d prior to harvest as opposed to 14 d. Vine management, tuber skin set, and yield were comparable when potato vines were flail chopped followed by flame burning and where diquat was applied twice, offering a viable program for smaller scale or organic production.

Nomenclature: Diquat; potato, Solanum tuberosum L.

Stakeholders were surveyed across Nebraska to identify the problem weeds and assess common weed management practices. A total of 425 responses were returned across four Nebraska extension districts (Northeast, Panhandle, Southeast, and West Central). Collectively, 61.2% of total farmed or scouted areas in Nebraska were under no-till production, and corn and soybean were the major crops (82.3% of total farmed or scouted area). Common waterhemp, horseweed, and kochia were the most problematic weeds statewide. Widespread occurrence of glyphosate-resistant (GR) weeds such as common waterhemp, horseweed, kochia, and Palmer amaranth were a serious problem in GR crop production. Additionally, 60% of growers in Nebraska reported the presence of at least one GR weed species on their farms. The most commonly used preplant burndown herbicides were 2,4-D and glyphosate, followed by saflufenacil and dicamba. In Nebraska, 74% and 59% of corn and soybean growers, respectively, were using PRE herbicides; however, more than 80% of growers were using POST herbicides for in-crop weed management. Atrazine alone or in premix or tank mix with mesotrione, S-metolachlor, or acetochlor were the most widely applied PRE herbicides in corn and grain sorghum, whereas the most commonly used PRE herbicides in soybean were the inhibitors of acetolactate synthase (ALS) and protoporphyrinogen oxidase (PPO). Glyphosate was the most frequent choice of the survey respondents as a POST herbicide in GR corn and soybean; 2,4-D was the most commonly used POST herbicide in grain sorghum and wheat. In Nebraska, only 5.2% of total crop area was planted with glufosinate-resistant crops. Most of the respondents (89%) were aware of the new multiple herbicide–resistant crops, and 80% of them listed physical drift and volatility of the auxinic herbicides as their primary concern. Fortyeight percent of survey respondents identified herbicide-resistant weed management as their primary research and extension priority.

Nomenclature: 2,4-D; acetochlor; atrazine; glufosinate; glyphosate; mesotrione; S-metolachlor; common waterhemp, Amaranthus rudis J.D. Sauer; horseweed, Conyza canadensis (L.) Cronq.; kochia, Kochia scoparia (L.) Schrad.; Palmer amaranth, Amaranthus palmeri S. Wats.; corn, Zea mays L.; grain sorghum, Sorghum bicolor (L.) Moench ssp. bicolor; soybean, Glycine max (L.) Merr.; wheat, Triticum aestivum L.