Weed control remains a major challenge for economically viable grain sorghum production in the southeastern United States due to crop sensitivity to weed competition during early growth stages. Field experiments were conducted in 2012 and 2013 to determine the effects of grain sorghum row spacing, population density, and herbicide programs on Palmer amaranth control, crop growth, and grain yield. Treatments included row spacings of 19, 38, and 76 cm; grain sorghum population densities of 99,000, 198,000, 297,000, and 396,000 plants ha^-1; and three herbicide programs: (1) a nontreated control, (2) S-metolachlor at 1,410 g ai ha^-1 plus atrazine at 1,820 g ha^-1 PRE, and (3) S-metolachlor at 1,070 g ha^-1 plus atrazine at 1,380 g ha^-1 PRE followed by 2,4 D at 330 g ha^-1 POST. Palmer amaranth control benefited from the addition of a POST herbicide and from crop density≥297,000 plants ha^-1. Under weedy conditions, Palmer amaranth density was not affected by narrower row spacing or increased crop density, whereas its dry biomass was reduced by 33% with 19 and 38 compared to 76 cm rows, and by 43% with≥297,000 vs 99,000 plants ha^-1. Row spacing had no effect on light interception by the crop canopy. However, crop density influenced canopy closure with maximum light interception occurring one and a half weeks earlier for density ≥297,000 plants ha^-1. Yield increased by 18% for 19 vs 38 and 76 cm rows, whereas grain crop density had no effect. Overall, these results indicate that the combination of row spacing ≤30 cm and crop density ≥297,000 plants ha^-1 provided at least 97% Palmer amaranth control in the absence of POST application and reduced its biomass by 32% in nontreated plots compared to 76 cm row spacing and crop density≤198,000 plants ha^-1.

Nomenclature: Atrazine; S-metolachlor; 2,4-D; Palmer amaranth; Amaranthus palmeri S. Wats.; sorghum, Sorghum bicolor (L.) Moench ssp. bicolor.

Weed management systems were established near Lubbock, TX in 2013, 2014, and 2015 to assess the effectiveness of premixed 2,4-D choline glyphosate alone and in combination with glufosinate and soil-residual herbicides for Palmer amaranth control. Systems consisted of trifluralin applied preplant incorporated followed by an early POST application followed by a mid-POST application. Palmer amaranth control 21 days after the early POST application ranged from 75 to 90% for all treatments that included 2,4-D choline glyphosate alone or in a tank-mixture in 2013. Twentyeight days after the mid-POST application, Palmer amaranth was controlled 86 to 99% for all herbicide systems with the exception of systems that included a mid-POST application of glufosinate alone. Combined across 2014 and 2015, Palmer amaranth control 21 days after the early POST application ranged from 96 to 98% for all systems that included 2,4-D choline glyphosate, 2,4-D choline alone, or 2,4-D choline in a tank-mixture. Combined across 2014 and 2015, Palmer amaranth control 28 days after the mid-POST application ranged from 95 to 100% with the exception of the following: trifluralin preplant incorporated followed by glufosinate with or without acetochlor applied early POST followed by glufosinate mid-POST and trifluralin preplant incorporated followed by glyphosate early POST followed by glyphosate mid-POST. Overall, numerous effective systems were identified; however, systems containing 2,4-D choline glyphosate or 2,4-D choline early POST and/or mid-POST were among the most effective. Glyphosate or glufosinate only systems or systems that relied on glufosinate alone at the mid-POST timing were inconsistent and often performed poorly.

Nomenclature: 2,4-D choline; glyphosate; glufosinate; Palmer amaranth, Amaranthus palmeri S. Wats.; cotton, Gossypium hirsutum L.

In recent years, horseweed has become an increasing problem in Montana. To confirm and characterize the level of glyphosate resistance, seeds were collected from putative glyphosate-resistant (GR) horseweed (GR-MT) plants in a wheat—fallow field in McCone County, MT. Known GR (GR-NE) and glyphosate-susceptible (GS-NE) horseweed accessions from Lincoln, NE, were included for comparison in dose—response and shikimate accumulation studies. Whole-plant glyphosate dose—response experiments conducted at the early- (5- to 8-cm diameter) and late- (12- to 15-cm diameter) rosette stages of horseweed indicated that GR-MT accessions had a 2.5- to 4.0-fold level of resistance to glyphosate relative to the GS-NE accession, on the basis of shoot dry weight (GR₅₀ values). The level of resistance was 3.1- to 7.9-fold on the basis of visually assessed injury estimates (I₅₀ values). At the whole-plant level, about 2.1- to 4.5-fold higher shikimate accumulation was observed in the GS-NE accession compared with the GR-MT and GR-NE accessions over a 10-d period after glyphosate was applied at 1,260 g ae ha^-1. In a separate greenhouse study, all three horseweed accessions were also screened with alternate POST herbicides registered for use in wheat—fallow rotations. The majority of the tested herbicides provided ≥90% injury at the field-use rates for all three horseweed accessions 3 wk after treatment. This is the first published report on the occurrence of GR horseweed in Montana cereal production. Increased awareness and adoption of best management practices, including the use of diversified (based on multiple sites of action) herbicide programs highlighted in this study, would aid in mitigating the further spread of GR horseweed in the cereal production fields of the U.S. Great Plains.

Nomenclature: Glyphosate; horseweed, Conyza canadensis (L.) Cronq.; wheat, Triticum aestivum L.

Glyphosate-resistant (GR) common waterhemp is the fifth GR weed species confirmed in Canada, and the fourth in Ontario. As of 2017, GR common waterhemp has been confirmed in Lambton, Essex, and Chatham-Kent counties in Ontario. Greenhouse and field dose-response experiments revealed that GR common waterhemp in Ontario had a resistance level of 4.5 and 28, respectively, when compared with known glyphosate-susceptible populations. At 12 wk after application, pyroxasulfone/flumioxazin (240 g ai ha^-1), pyroxasulfone/sulfentrazone (300 g ai ha^-1), and S-metolachlor/metribuzin (1,943 g ai ha^-1) controlled GR common waterhemp 97%, 92%, and 87%, respectively. Pyroxasulfone/sulfentrazone or S-metolachlor/metribuzin applied PRE followed by acifluorfen (600 g ai ha^-1) or fomesafen (240 g ai ha^-1) applied POST controlled GR common waterhemp 98% and performed better than PRE or POST alone. This research is the first to determine the resistance factor of GR common waterhemp in Ontario and identifies control strategies in soybean to mitigate the impact of common waterhemp interference in soybean crop production.

Nomenclature: Acifluorfen; flumioxazin; fomesafen; glyphosate; S-metolachlor; metribuzin; pyroxasulfone; sulfentrazone; common waterhemp, Amaranthus tuberculatus var. rudis; soybean, Glycine max (L.) Merr.

Field studies were conducted in 2014 and 2015 in Tennessee to examine pyroxasulfone dissipation under field conditions of winter wheat production. Three formulations were examined: (1) a single component active ingredient in an 85% dry flowable, (2) dry flowable formulation in combination of pyroxasulfone flumioxazin, and (3) a liquid SC formulation of pyroxasulfone carfentrazone. The liquid formulation is a suspo-emulsion. When averaged across the three studies, the DT 50 were 34.4, 30.2 and 29.9 d for pyroxasulfone plus carfentrazone, pyroxasulfone, and pyroxasulfone plus flumioxazin, respectively. These trends would indicate that formulation had little or no effect on pyroxasulfone dissipation in this experiment. Pyroxasulfone DT 50 in all studies ranged from a low of 15.4 d to a high of 53.3 d, and loss was more rapid under warm, moist conditions. These results indicate that pyroxasulfone would last long enough to provide residual weed control, but would not persist excessively to injure rotational crops.

Nomenclature: Pyroxasulfone; wheat, Triticum aestivum L.

Glyphosate-resistant (GR) common waterhemp (CW) is a localized weed in Ontario and one of the most problematic weeds in the US Corn Belt. First confirmed in Ontario in 2014, GR CW has now been confirmed in forty fields in three counties in Ontario as of 2015. Historically, the primary POST herbicides used for the control of CW in soybean were glyphosate, acifluorfen and fomesafen, but resistance to all three has been confirmed in many US states. Research was conducted in 2015 and 2016 to determine the control of GR CW with some of the new herbicide-resistant soybean technologies including glufosinate (LibertyLink), 2,4-D and glyphosate (Enlist), and isoxaflutole, mesotrione, and glufosinate (HPPD-resistant). Glyphosate-resistant CW was controlled (≥ 90%) all season with a two-pass weed control system across all herbicide-resistant soybean technologies evaluated. The two-pass weed control system in this research is defined as a PRE herbicide followed by a POST herbicide. At 12 WAA, the two-pass programs in LibertyLink, Enlist, and HPPDresistant systems controlled GR CW up to 98, 98, and 92%, respectively, and reduced GR CW densities to 0 to 2% of the weedy control at 4 WAA. The two-pass programs provided greater GR CW control than PRE or POST herbicides alone. This study found that the use of two-pass weed control programs in glufosinate-resistant, glyphosate DMA/2,4-D choline-resistant and HPPD-resistant soybean can provide excellent control of GR CW, and can be valuable tools to reduce the selection intensity for herbicide-resistant weeds. Through the rotational use of different technologies, growers may be able to better manage their weed populations in reducing the risk of resistance when compared to the use of one herbicide repeatedly.

Nomenclature: Glufosinate; glyphosate; common waterhemp, Amaranthus rudis Sauer; soybean; Glycine max (L.) Merr.

Imazapyr and imazamox are frequently applied postemergence to control grass and broadleaf weeds in imidazolinone-resistant sunflower in Argentina. Herbicide carryover to rotational crops represents a disadvantage of these herbicides, particularly in regions with low rainfall during the months prior to rotational crop sowing. Between 2009 and 2012, field and greenhouse studies were conducted on four important sunflower-cropped areas of Argentina. The objective was to quantify the effects of imazapyr alone and imazamox plus imazapyr applied in sunflower crops on the subsequent establishment, growth, and yield of barley, oat, and wheat. In all field experiments, imazapyr alone and imazamox plus imazapyr were applied at recommended rates (80 g ha^-1 and 66 plus 30 g ha^-1, respectively), and also, in some experiments, at double the recommended rates. Soil bioassays were also conducted in the greenhouse to study the effect of these herbicides on barley, oat, and wheat seedlings. The mixture of imazamox plus imazapyr was safer for rotational crops than imazapyr applied alone, because of the reduced rate of imazapyr in the mixture treatments. Barley was more sensitive to imidazolinones, particularly imazapyr, than the other winter cereals. Imazapyr at double rate (160 g ha^-1) reduced barley yield by 45% when seeds were sown 165 d after herbicide application and with 240mm rainfall after herbicide application.

Nomenclature: Imazamox; imazapyr; barley, Hordeum vulgare L.; oat, Avena sativa L.; sunflower, Helianthus annuus L.; wheat, Triticum aestivum L.

Field dodder is an important weed in alfalfa grown for seed, and stringent control is required to keep the alfalfa seed from becoming contaminated with dodder seed. Pendimethalin has been the primary tool used to control dodder in alfalfa seed production for more than 25 yr. Flumioxazin was recently registered in alfalfa seed and forage crops, but its activity on field dodder was unknown. Control of field dodder with flumioxazin and pendimethalin was compared in greenhouse trials in a loamy sand soil. The number of emerged dodder seedlings able to twine on a simulated host were counted weekly for a 4-wk period following herbicide application. Flumioxazin applied at the alfalfa field use rate of 0.14 kg ai ha^-1 completely controlled dodder over the initial 4-wk period. Dodder either failed to emerge or emerged and died without twining on the simulated host in the 4-wk period. When dodder was reseeded after 4 wk in flumioxazin-treated soil, the number of twined dodder seedlings was reduced by 56% in one trial but was unaffected in a second trial compared with nontreated checks. In the initial 4-wk period following herbicide application, flumioxazin controlled field dodder similar to pendimethalin applied at 2.2 and 4.4 kg ai ha^-1 in both trials. However, after additional dodder seed was planted at 4 wk after treatment, dodder was suppressed more by pendimethalin than flumioxazin in the additional 4-wk period. Flumioxazin offers alfalfa seed and forage producers a new mode of action to manage early-emerging field dodder.

Nomenclature: Flumioxazin; pendimethalin; field dodder, Cuscuta pentagona Engelm.; alfalfa, Medicago sativa L.

Management of volunteer horseradish is a challenge when it is grown in rotation with other crops, such as corn and soybean. Although volunteer horseradish may not cause yield loss, these plants serve as hosts for various soilborne pathogens that damage subsequent horseradish crops. In addition to volunteer horseradish, glyphosate-resistant Palmer amaranth is becoming difficult to control in southwestern Illinois, as a consequence of the plant's ability to withstand glyphosate and drought, produce many seeds, and grow rapidly. Field studies were conducted to evaluate the effect of glyphosate and dicamba on volunteer horseradish and Palmer amaranth control in 2014 and 2015. Glyphosate alone (1,265 and 1,893 g ae ha-1) and glyphosate plus dicamba at the high rate (1,680 g ae ha-1) provided the greatest volunteer horseradish control, ranging from 81% to 89% and 90% to 93%, respectively. Measures of root biomass reduction followed similar trends. Glyphosate alone provided the greatest reduction in volunteer horseradish root viability (79% to 100%) but was similar in efficacy to applications of glyphosate plus dicamba in most comparisons. Efficacy of PRE-only applications on Palmer amaranth control ranged from 92% to 99% control in 2014 and 68% to 99% in 2015. However, PRE-only applications were often similar in efficacy to PRE followed by (fb) glyphosate plus dicamba applied POST. Treatments containing flumioxazin did not control Palmer amaranth as well as other treatments. POST applications alone were not effective in managing Palmer amaranth. Many of the PRE fb POST treatment options tested will improve resistance management over PRE-only treatments, provide control of Palmer amaranth, and allow horseradish to be planted the following spring.

Nomenclature: Dicamba; flumioxazin; glyphosate; horseradish, Armoracia rusticana P.G. Gaertn., B. Mey. & Scherb. ARWLA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; corn, Zea mays L.; soybean, Glycine max (L.) Merr.

Field studies were conducted to determine the influence of herbicides on the development of internal necrosis (IN) in sweetpotato storage roots. In a slip propagation study, herbicide treatments included PRE application (immediately after covering seed roots with soil) of clomazone (0.42, 0.84 kg ai ha^-1), flumioxazin (0.11, 0.21 kg ai ha^-1), fomesafen (0.28, 0.56 kg ai ha^-1), linuron (0.56, 1.12 kg ai ha^-1), S-metolachlor (0.8, 1.6 kg ai ha^-1), flumioxazin plus S-metolachlor (0.11 0.8 or 1.6 kg ha^-1), and napropamide (1.12, 2.24 kg ai ha^-1), and POST application (2 to 4 wk prior to cutting slips) of ethephon (0.84, 1.26 kg ai ha^-1) and paraquat (0.14, 0.28 kg ai ha^-1). In a field production study, flumioxazin, fomesafen, linuron, and paraquat were applied PREPLANT (one d prior to sweetpotato transplanting), clomazone, S-metolachlor, and napropamide were applied PRE [4 d after transplanting (DAP)], flumioxazin PREPLANT followed by (fb) S-metolachlor PRE, and ethephon applied POST (2 wk prior to harvest). Herbicide rates were similar to those used in the slip propagation study. Yield of sweetpotato in both studies was not affected by herbicide treatment. In both studies, IN incidence and severity increased with time and was greatest at 60 d after curing. No difference was observed between herbicide treatments for IN incidence and severity in the slip production study which indicates herbicide application at time of slip propagation does not impact the development of IN. In the field production study, the only treatment that increased IN incidence compared to the nontreated was ethephon with 53% and 2.3 incidence and severity, respectively. The presence of IN affected roots in nontreated plots indicates that some other pre- or post-curing factors other than herbicides are responsible for the development of IN. However, the ethephon application prior to sweetpotato root harvest escalates the development of IN.

Nomenclature: Clomazone; ethephon; flumioxazin; fomesafen; linuron; napropamide; paraquat; S-metolachlor; sweetpotato, Ipomoea batatas (L.) Lam.

Broadleaves, grasses, and nutsedge species are persistent problems with limited management options for strawberry growers in Florida. Field experiments were conducted in 2015-2016 (year 1) and 2016-2017 (year 2) at the Gulf Coast Research and Education Center in Balm, FL, to evaluate weed control and strawberry tolerance to herbicides applied through the drip irrigation. 2940 g ai ha-1 EPTC, 105 g ai ha-1 flumioxazin, 570 g ai ha-1 fomesafen, 52 g ai ha-1 halosulfuron, 3585 g ai ha-1 napropamide, oxyfluorfen 560 g ai ha-1, and 1070 g ai ha-1 S-metolachlor were applied through a single drip tape at 7 or 14 d prior to transplanting. Halosulfuron was the most injurious herbicide, causing 18 and 46% injury at 35 d after transplanting (DATP) in year 1 when the herbicide was applied 7 and 14 d prior to transplanting, respectively. However, strawberry plants recovered from the initial injury and there was no reduction in total berry yield. None of the other herbicides evaluated elicited significant crop injury nor reduced berry yield. Averaged over application timings, EPTC, fomesafen, and napropamide suppressed yellow nutsedge emergence to 49, 64, and 41% of the nontreated control, respectively. Flumioxazin, fomesafen, and halosulfuron suppressed black medic emergence to 55, 52, and 55% of the nontreated control, respectively. None of the herbicides evaluated adequately suppressed Carolina geranium. Overall, results suggest that the evaluated herbicides with the exception of halosulfuron are safe for use on strawberry and would give growers an alternative management option. Drip-applied herbicides permit application closer to the transplant date and would be helpful as part of a weed control program for weed suppression.

Nomenclature: EPTC; flumioxazin; fomesafen; halosulfuron; napropamide; oxyfluorfen; S-metolachlor; Carolina geranium, Geranium carolinianum L.; purple nutsedge, Cyperus rotundus L.; strawberry, Fragaria × ananessa (Weston) Duchesne ex Rozier.

Carinata is a new biofuel crop that was recently introduced in the southeastern USA as a winter crop. This crop is competitive after canopy closure, but there is a need for weed control options at earlier growth stages. Field experiments were conducted from 2014 to 2016 to determine the safety of several PRE and POST herbicides in carinata. Pendimethalin at 1080 g ai ha^-1 applied preplant incorporated (PPI) and PRE caused no carinata injury, or plant density and yield reductions. S-metolachlor was also safe at 694, 1070, 1390, and 2780 g ai ha^-1 applied at PRE, 3 d after planting (DAP) and at the 2- to 6-leaf stage. Flumioxazin at 72 g ai ha^-1 applied PRE was highly injurious on carinata preventing its establishment. Among the POST herbicides evaluated, clopyralid at 210 g ae ha1 and clethodim at 136 g ai ha^-1 caused minor injury to carinata but did not reduce yield compared to the nontreated control. Acifluorfen at 420 g ai ha^-1, bentazon at 840 g ai ha^{-1, and carfentrazone at 18 g ai ha-1} applied POST to carinata caused 75 to 100% injury. Under stressful conditions (i.e. high summer temperatures) all POST herbicides caused more injury than under more favorable conditions for growth in Florida (i.e. winter). The present study identified pendimethalin, S-metolachlor, clopyralid and clethodim as potential herbicides for weed control in carinata, and flumioxazin, acifluorfen, bentazon, and carfentrazone as herbicides that can be used to control volunteer carinata plants in rotational crops.

Nomenclature: Acifluorfen; bentazon; carfentrazone; flumioxazin; pendimethalin; S-metolachlor; carinata, Brassica carinata A. Braun.

Prodiamine is a dinitroaniline herbicide labeled for PRE control of goosegrass in warm- and cool-season turfgrass. In 2013, several golf course roughs in Maryville, TN reported poor goosegrass control (< 20%) following prodiamine treatment at 1,120 g ai ha^-1. We harvested suspected prodiamine-resistant (PR) and prodiamine-susceptible (S) goosegrass phenotypes from the field and exposed them to a range of increasing prodiamine concentrations in hydroponic culture. Exposure to prodiamine at 0.001mM reduced root growth of the S phenotype to 11% of the non-treated check. By comparison, exposure to 0.001mM prodiamine had minimal effect on the PR phenotype, as root growth was 94% of the non-treated check. Molecular analyses revealed that PR plants contained a threonine (Thr) to isoleucine (Ile) substitution at position 239 on the α-tubulin 1 (TUA1) protein. The substitution, found in all PR plants, is the mechanism of prodiamine resistance in this phenotype. In field studies, topramezone controlled PR goosegrass 72% to 89% by 50 d after treatment (DAT) compared to only 22% to 23% for foramsulfuron. Topramezone treatment injured bermudagrass 34% to 60% from 7 to 14 DAT; however, injury was ≤6% 28 DAT and 0% by the end of the study. Our results indicate that POST applications of topramezone can control dinitroaniline-resistant goosegrass. In addition, we established an easy-to-use genotyping assay to quickly screen goosegrass phenotypes for a target-site mutation (Thr-239-Ile) on TUA1 associated with resistance to dinitroaniline herbicides such as prodiamine. Future research should work to expand this assay for use with other weed species and herbicidal modes of action.

Nomenclature: Foramsulfuron; prodiamine; topramezone; goosegrass, Eleusine indica L. Gaertn.; bermudagrass, Cynodon dactylon L. Pers.

Weed management in the organic Vidalia^® sweet onion production system is largely dependent on multiple cultivations with a tine weeder. Earlier research suggested cultivation with a tine weeder did not predispose onion bulbs to infection during storage. Trials were conducted from 2012 through 2014 near Lyons, GA, to determine the interactive effects of cultivation, weed removal, and a biofungicide on weed densities, onion yield, grade, and diseases of stored onion. Cultivation twice or four times at biweekly intervals with a tine weeder reduced densities of cutleaf evening-primrose, lesser swinecress, and henbit compared with the noncultivated control, although weeds surviving cultivation were very large and mature at harvest. Cultivation generally improved onion yields over the noncultivated control, except in 2014, when baseline weed densities were high and weeds surviving cultivation were numerous. Weeds removed by hand weeding improved onion yields, but that effect was independent of cultivation. Four applications of a biofungicide derived from giant knotweed had no effect on onion yield. Cultivation had no effect on incidence of the fungal disease botrytis neck rot, with inconsistent effects on the bacterial diseases center rot and sour skin. Weed removal with hand weeding did not affect diseases of stored onion. The biofungicide had no effect on diseases of stored onion. These results demonstrate the limitations of cultivation when cool-season weed infestations are dense. With no interactions among main effects, weed control and onion yield response to cultivation and hand weeding are independent. Cultivation for weed control is much less costly than hand weeding. With no interaction between the cultivation and weed removal main effects, it is not necessary to supplement tine weeder cultivation with costly hand weeding.

Nomenclature: Cutleaf evening-primrose, Oenothera laciniata Hill; giant knotweed, Reynoutria sachalinensis (F. Schm.) Nakai; henbit, Lamium amplexicaule L; lesser swinecress, Coronopus didymus (L.) Sm.; dry-bulb onion, Allium cepa L.

Slow carrot emergence and canopy development render the crop a poor competitor with weeds. In this study, the ability to suppress weeds and maintain yield in the presence of weeds was compared among nine carrot varieties that included those selected by plant breeders for rapid vegetative canopy development compared to traditional varieties. Two weed management treatments were compared: handweeding for 21 d after carrot seeding versus handweeding for the entire carrot season. In years and locations with low to moderate weed pressure, such as in the 2014 study, differences among carrot varieties in weed competitiveness or tolerance were less apparent and therefore less relevant. Maximum carrot yield loss to weed competition among varieties was 28% in 2014. Yield loss in the presence of weeds was 15% or less with six of the nine carrot varieties. However, when weed pressure was intense in the 2015 study, both carrot plant density and carrot canopy development were inversely related to weed biomass. Carrot yield loss in the presence of weeds ranged from 38 to 87%. Despite correcting seeding populations for differences in germination among carrot varieties, carrot stand establishment varied greatly and would likely affect subsequent weed control measures such as timely cultivation or herbicide application. Future research efforts are warranted that consider carrot stand establishment factors and their relationship with integrated weed management programs.

Nomenclature: Carrot, Daucus carota L. var. sativus Hoffm.

Field studies were conducted in Clinton, NC in 2007 and 2009 to determine sweetpotato crop response and Palmer amaranth control with metribuzin and oryzalin. Treatments consisted of 140 and 202 g ai ha^-1 metribuzin applied immediately after transplanting [0 wk after transplanting (WAP)] or 2 WAP, 560 and 1121 g ha^-1 oryzalin 0 WAP, and tank mixes of metribuzin (140 or 202 g ha^-1) and oryzalin (560 or 1,121 g ha^-1) 0 WAP. At 2 WAP, metribuzin alone applied 0 WAP resulted in greater crop injury (33%) than oryzalin alone (1%), and the tank mix of metribuzin plus oryzalin resulted in greater crop injury (49%) than either herbicide applied alone. Greater crop injury occurred when metribuzin was applied at 202 g ha^-1 (54%) than 140 g ha^-1 (34%). Levels of injury were similar at 4 WAP (34, 8, and 52% for metribuzin, oryzalin, and the tank mix, respectively). At 4 WAP, injury from metribuzin was greater when it was applied 0 WAP (34%) compared to 2 WAP (18%). By 10 WAP, injury from metribuzin applied at 2 WAP was only 4%. At 4 WAP, Palmer amaranth control was excellent for all treatments and ≥98%. At 10 WAP, control among treatments ranged from 77% to 85%. Palmer amaranth control provided by metribuzin was similar for applications made 0 WAP (78%) and 2 WAP (77%). Oryzalin alone provided similar control (85%) to metribuzin alone 0 WAP, but greater control than the tank mix (77%). Neither metribuzin nor oryzalin rate differed in weed control provided at 10 WAP. Oryzalin 0 WAP and metribuzin 2 WAP provided no. 1 sweetpotato yields equivalent to the hand-weeded check. No. 1 yields of all other treatments were less than the hand-weeded check but greater than the weedy check.

Nomenclature: Metribuzin; oryzalin; Palmer amaranth, Amaranthus palmeri S. Wats.; sweetpotato, Ipomoea batatas L. Lam. ‘Beauregard’ and ‘Covington’

Grafted plants are a combination of two different interspecific or intraspecific scion and rootstock. Determination of herbicidal selectivity of the grafted plant is critical given their increased use in vegetable production. Differential absorption, translocation, and metabolism play an important role in herbicide selectivity of plant species because these processes affect the herbicide amount delivered to the site of action. Therefore, experiments were conducted to determine absorption, translocation, and metabolism of halosulfuron in grafted and non-grafted tomato and eggplant. Transplant type included non-grafted tomato cultivar Amelia, non-grafted eggplant cultivar Santana, Amelia scion grafted onto Maxifort tomato rootstock (A-Maxifort) and Santana scion grafted onto Maxifort rootstock (S-Maxifort). Plants were treated POST with commercially formulated halosulfuron at 39 g ai ha^-1 followed by ¹⁴C-halosulfuron under controlled laboratory conditions. Amount of ¹⁴C-halosufuron was quantified in leaf wash, treated leaf, scion shoot, rootstock shoot, and root at 6, 12, 24, 48, and 96 h after treatment (HAT) using liquid scintillation spectrometry. No differences were observed between transplant types with regard to absorption and translocation of ¹⁴C-halosulfuron. Absorption of ¹⁴C-halosulfuron increased with time, reaching 10 and 74% of applied at 6 and 96 HAT, respectively. Translocation of ¹⁴C-halosulfuron was limited to the treated leaf, which reached maximum (66% of applied) at 96 HAT, whereas minimal (<4% of applied) translocation occurred in scion shoot, rootstock shoot, and root. Tomato plants metabolized halosulfuron faster compared to eggplant regardless of grafting. Of the total amount of ¹⁴C-halosulfuron absorbed into the plant, 9 to 14% remained in the form of the parent compound in tomato compared with 25 to 26% in eggplant at 48 HAT. These results indicate that grafting did not affect absorption, translocation, and metabolism of POST halosulfuron in tomato and eggplant.

Nomenclature: Halosulfuron; eggplant, Solanum melongena L.; tomato, Solanum lycopersicum L.

Palmer amaranth is the most troublesome weed problem in mid-southern US crop production. Herbicides continue to be the most commonly employed method for managing Palmer amaranth, despite the weed's widespread resistance to them. Therefore, farmers need research and extension efforts that promote the adoption of integrated weed management (IWM) techniques. Producers, crop consultants, educators, and researchers would be more likely to deploy diversified chemical and nonchemical weed management options if they are more informed about long-term biological and economic implications via user-friendly decision-support software. Described within is a recently developed software that demonstrates the effects of Palmer amaranth management practices on soil seedbank, risk of resistance evolution, and economics over a 10-year planning horizon. Aiding this objective is a point-and-click interface that provides feedback on resistance risk, yield potential, profitability, soil seedbank dynamics, and error checking of management options.

Nomenclature: Palmer amaranth, Amaranthus palmeri S. Wats.

Triclopyr is a synthetic auxin herbicide currently available as a triethylamine salt, butoxyethyl ester, pyridinyloxyacetic acid, or choline salt. The formulation of a herbicide has the potential to impact its activity; therefore, the objective of this study was to determine the relative activity of these four triclopyr formulations. Greenhouse dose-response studies were conducted twice at the University of Florida in 2015. The four formulations were foliar applied at rates ranging from 17 to 1,121 g ae ha^-1 to 2- to 3-leaf soybean, sunflower, tomato, and cotton. The amine salt formulation provided the lowest ED₅₀ values in tomato and sunflower (22.87 and 60.39 g ha^-1, respectively); whereas in soybean, amine and choline formulations provided the lowest ED₅₀ values (22.56 and 20.95 g ha^-1, respectively). No differences between formulations were observed in cotton. These data suggest that (1) the amine salt formulation of triclopyr might be more active than the others on tomato and sunflower, and (2) the amine and choline salt formulations might be more active than the others on soybean. Further work must be conducted to determine whether there are differences among these formulations under a range of field conditions and target species. In addition, other important management factors such as applicator safety, volatility potential, and cost should be considered when choosing the best formulated product to be applied.

Nomenclature: Triclopyr; cotton, Gossypium hirsutum L.; soybean, Glycine max (L.) Merr.; sunflower, Helianthus annuus L.; tomato, Solanum lycopersicum L.