Field trials were conducted in 2013 and 2014 to investigate the tolerance of limpograss to increasing rates of hexazinone. Dose-response curves were generated using linear and quadratic regression models to determine the hexazinone estimated dose (ED) required to provide 10% (ED10) and 20% (ED20) of visual injury and herbage mass reduction. The ED10 and ED20 for visual estimates of injury were estimated to be 0.05 and 0.14 kg ai ha-1 at 60 d after treatment (DAT). Regarding forage herbage mass reduction, the ED10 and ED20 were estimated to be 0.07 and 0.19 kg ai ha-1 in 2013, whereas in 2014, the ED10 and ED20 were estimated to be 0.03 and 0.06 kg ai ha-1, respectively. The significant difference in herbage mass reduction between 2013 and 2014 was likely due to rainfall patterns, which possibly promoted hexazinone leaching in 2013 and consequently, less activity. Overall, hexazinone resulted in high degrees of limpograss injury across all response variables in both years; therefore, smutgrass control in limpograss pastures with hexazinone may not be a viable option. The presence or absence of smutgrass should be considered before limpograss establishment as there is no viable herbicide to selectively remove smutgrass from limpograss swards.

With the recent introductions of glyphosate- and dicamba-tolerant crops, such as soybean and cotton, there will be an increase in POST-applied tank-mixtures of these two herbicides. However, few studies have been conducted to evaluate drift from dicamba applications. This study aimed to evaluate the effects of dicamba with and without glyphosate sprayed through standard and air induction flat-fan nozzles on droplet spectrum and drift potential in a low-speed wind tunnel. Two standard (XR and TT) and two air induction (AIXR and TTI) 110015 nozzles were used. The applications were made at 276 kPa pressure in a 2.2 ms−1 wind speed. Herbicide treatments evaluated included dicamba alone at 560 gaeha−1 and dicamba+glyphosate at 560+1,260 gaeha−1. The droplet spectrum was measured using a laser diffraction system. Artificial targets were used as drift collectors, positioned in a wind tunnel from 2 to 12 m downwind from the nozzle. Drift potential was determined using a fluorescent tracer added to solutions, quantified by fluorimetry. Dicamba droplet spectrum and drift depended on the association between herbicide solution and nozzle type. Dicamba alone produced coarser droplets than dicamba+glyphosate when sprayed through air induction nozzles. Drift decreased exponentially as downwind distance increased and it was reduced using air induction nozzles for both herbicide solutions.

Palmer amaranth is the most problematic weed in agronomic crop production fields in the United States. A Palmer amaranth biotype was not controlled with sequential applications of glyphosate in glyphosate-resistant (GR) soybean production field in south-central Nebraska. The seeds of the putative GR Palmer amaranth biotype were collected in the fall of 2015. The objectives of this study were to (1) confirm GR Palmer amaranth and determine the level of resistance in a whole-plant dose-response bioassay, (2) determine the copy number of 5-enolpyruvylshikimate-3-phosphate (EPSPS) gene, the molecular target of glyphosate, and (3) evaluate the response of GR Palmer amaranth biotype to POST corn and soybean herbicides with different modes-of-action. Based on the effective dose required to control 90% of plants (ED90), the putative GR Palmer amaranth biotype was 37- to 40-fold resistant to glyphosate depending on the glyphosate-susceptible (GS) used as a baseline population. EPSPS gene amplification was present in the GR Palmer amaranth biotype with up to 32 to 105 EPSPS copies compared to the known GS biotypes. Response of GR Palmer amaranth to POST corn and soybean herbicides suggest reduced sensitivity to atrazine, hydroxyphenylpyruvate dioxygenase (HPPD)- (mesotrione, tembotrione, and topramezone), acetolactate synthase (ALS)- (halosulfuron-methyl), and protoporphyrinogen oxidase (PPO)- (carfentrazone and lactofen) inhibitors. GR Palmer amaranth was effectively controlled (>90%) with glufosinate applied at 593 g ai ha−1 with ≥95% reduction in biomass. More research is needed to determine whether this biotype exhibits multiple resistant to other group of herbicides and evaluate herbicide programs for effective management in corn and soybean.

Archaeological sites of the Mediterranean region are widely colonized by weed species causing various problems both to the monuments and the functionality of the sites. Due to recent regulatory restrictions for herbicide use at archaeological sites, flame weeding was studied as an alternative weed management method. The objective of the study was to test two propane doses (99 kg ha−1 and 129 kg ha−1) applied two, three, or four times at three archaeological sites of Greece (Kolona, Ancient Messene and Early Christian Amfipolis). Percent weed control and weed heights were significantly affected by flaming treatments. Visual evaluation of percent weed control suggested that the propane dose of 129 kg ha−1 applied four times provided excellent weed control (>90%) for over 2 months. Annual broadleaf weeds were controlled better with flaming than grasses and perennial broadleaf species. The high propane dose applied four times reduced average vegetation height to about 10 cm, which was the desirable vegetation height wanted by the managers of the archeological sites suggesting that flame weeding has the potential to be used effectively for weed management in archaeological sites of the Mediterranean region.

Adoption of conservation tillage practices has been slow in organic vegetable production, partially due to producers’ concerns regarding weed management. Integrating cover crops into a conservation tillage program may provide organic producers a viable weed management option enabling growers to practice conservation tillage. A four-year study was conducted to evaluate the influence of different tillage methods (two conventional and two conservation practices) jointly with a mixed winter cover crop for weed suppression, time required for hand weeding, and crop yield in organically managed eggplant (2012 and 2014) and sweet corn (2013 and 2015) production systems. Tillage treatments were conventional tillage without surface mulch (CT-BG) and with black polyethylene (plastic) mulch (CT-BP), strip-tillage (ST), and no-tillage (NT) with cover crop residue. At 2 and 7 WAT/P (weeks after transplanting/planting), intra-row weed density was higher in CT-BG and ST, and inter-row weed density was higher in CT-BG and CT-BP treatments. Time required for hand-weeding was greatest in CT-BG and least in CT-BP and NT treatments. Eggplant yield was lowest in NT treatment in 2012 but similar among treatments in 2014. Sweet corn yield was similar among treatments in 2013 but highest in ST in 2015. Though both CT-BP and NT treatments showed greater potential for weed suppression, production input was highest in CT-BP but least in NT. Implications of these findings suggest that there is a potential to use strip tillage integrating with stale seedbed tactic for weed management in organic vegetables, which reduces herbicide use, hand-labor, and overall weed management cost while maintaining high yield potential.

Field studies were conducted at the Pontotoc Ridge-Flatwoods Branch Experiment Station in Pontotoc, MS in 2015 and 2016 to determine the influence of lay-by metribuzin application on weed control and sweetpotato crop response. With the exception of weedy and hand-weeded checks, all plots received flumioxazin at 107 gaiha−1 pre-transplanting followed by (fb) clomazone at 1,120 gaiha−1 immediately after transplanting. Lay-by treatments consisted of S-metolachlor (800 gaiha−1), metribuzin (210 or 315 gaiha−1), metribuzin (210 gha−1) plus napropamide (1,120 gaiha−1), and metribuzin (210 gha−1) plus S-metolachlor (800 gha−1). At 4 weeks after transplanting, sweetpotato crop injury was 3 to 15%, but was transient and not evident after 6 (2015) to 8 weeks after transplanting (2016). Season-long weed control was excellent (≥98%) for all herbicide treatments used in the study. Hand-weeded check plots yielded 4,600; 18,350; 28,770; and 1,520 kgha−1 of jumbo, No. 1, marketable, and cull grades, respectively. Jumbo, No. 1, and marketable yields from all herbicide-containing treatments in the study were greater than the weedy check and similar to the hand-weeded check. For all treatments, the portion of yield graded as cull was similar to the hand-weeded check. Canner yield response differed between years. In general, canner yield was greater in 2016 (8,460 to 10,670 kgha−1) than 2015 (1,570 to 3,570 kgha−1). In both years, canner yield in all treatments was similar to the hand-weeded check with one exception: in 2015 sweetpotato receiving metribuzin plus napropamide yielded more canners (3,570 kgha−1) than the hand-weeded check (2,300 kgha−1).

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.

Common ragweed is an important broadleaf weed in agronomic crops in the northcentral United States. A common ragweed biotype in glyphosate-resistant (GR) soybean production field in southeast Nebraska was not controlled after sequential applications of glyphosate at the labeled rate. The objectives of this study were to confirm GR common ragweed in Nebraska by quantifying the level of resistance in greenhouse and field whole-plant dose-response studies and to evaluate the response of the putative GR common ragweed to POST corn and soybean herbicides. Greenhouse whole-plant dose-response studies confirmed 7- and 19-fold resistance to glyphosate compared to the known glyphosate-susceptible (GS) biotype based on biomass reduction and control estimates, respectively. Field dose-response studies conducted in 2015 and 2016 at the putative GR common ragweed research site suggested that glyphosate doses equivalent to 15- and 40-times the labeled rate (1,260 gaeha–1) were required for 90% control and biomass reduction, respectively. Response of GR common ragweed to POST soybean herbicides in greenhouse studies indicated ≥89% control with acifluorfen, fomesafen, fomesafen plus glyphosate, glyphosate plus dicamba or 2,4-D choline, glufosinate, imazamox plus acifluorfen, and lactofen. POST corn herbicides, including 2,4-D, bromoxynil, diflufenzopyr plus dicamba, glufosinate, halosulfuron-methyl plus dicamba, mesotrione plus atrazine, and tembotrione provided ≥87% control, indicating that POST herbicides with distinct modes of action are available in corn and soybean for effective control of GR common ragweed. Results also suggested a reduced efficacy of the acetolactate synthase (ALS)-inhibiting herbicides tested in this study for control of GR and GS biotypes, indicating further research is needed to determine whether this biotype has evolved multiple herbicide resistance.

Treerow vegetation abundance and biodiversity were measured in response to six orchard floor management strategies in organic peach in northern Utah for three growing seasons. A total of 32 weed species were observed in the treerow; the most common were field bindweed, dandelion, perennial grasses (e.g., red fescue and ryegrass), clovers, and prickly lettuce. Weed biomass was two to five times greater in unmanaged (living mulch) than in manipulated treatments. Tillage greatly reduced weeds for approximately one month; however, vegetation rebounded midseason. Tillage selected for species adapted to disturbance, such as common purslane and field bindweed. Straw mulch provided equivalent weed suppression to tillage in the early season. Straw required annual reapplication with material costs, labor, and weed-seed contamination (e.g., volunteer grains and quackgrass) as disadvantages. Plastic fabric mulch reduced weeds the most, but had high initial costs and required seasonal maintenance. Weed biomass declined within seasons and across the three years of the study, likely due to tree canopy shading. Neither birdsfoot trefoil nor a perennial grass mixture planted in the alleyways influenced treerow weeds. Our results demonstrate several viable alternatives to tillage for weed management in treerows of organic peach orchards in the Intermountain West.

Two putative glyphosate-resistant (GR) Russian-thistle accessions were collected from fallow fields (wheat-fallow rotation): one from Choteau County, MT (MT-R), and a second from Columbia County, WA (WA-R) in summer/fall of 2015. Greenhouse and outdoor/field whole-plant dose-response studies were conducted to confirm and characterize the levels of glyphosate resistance in these GR accessions relative to known glyphosate-susceptible accessions (MT-S and WA-S from MT and WA, respectively). Based on GR50 values of the progeny plants, the MT-R accession exhibited 4.5-fold and 5.9-fold resistance to glyphosate relative to the MT-S accession under greenhouse and outdoor conditions, respectively. The WA-R accession showed 3.0- to 5.0-fold resistance relative to the WA-S accession in greenhouse experiments, and 1.9- to 7.5-fold resistance in multi-site field experiments. In a separate greenhouse study on alternative POST herbicides to control GR Russian-thistle, bicyclopyrone plus bromoxynil, bromoxynil plus fluroxypyr, bromoxynil plus pyrasulfotole, bromoxynil plus MCPA, paraquat alone, paraquat plus metribuzin, saflufenacil alone, saflufenacil plus 2,4-D, and 2,4-D plus bromoxynil plus fluroxypyr provided effective control (≥95%) and shoot dry weight reduction (up to 98%) of GR accessions. This research confirms the first global case of field-evolved GR Russian-thistle. Best management practices (BMPs); including alternative, effective herbicide programs (based on multiple mechanisms of action highlighted in this study) need immediate implementation to prevent further spread of GR or evolution of multiple HR Russian-thistle populations in this region.

Bell pepper producers are faced with the challenge of controlling weeds following the phase-out of methyl bromide (MBr). Numerous attempts have been made to find a single fumigant or herbicide to control a broad spectrum of weeds. Adequate weed control in bell pepper will likely require weed management systems utilizing both fumigant and herbicide options. A weed management system including the fumigant dimethyl disulfide (DMDS) plus chloropicrin (Pic) plus the herbicide napropamide prior to transplant followed by S-metolachlor POST may be necessary to replace MBr. Field experiments were conducted during 2010 and 2011 near Ty Ty, Georgia to determine bell pepper and weed response to DMDS plus Pic or in systems with napropamide and/or S-metolachlor. Bell pepper were not significantly injured by DMDS plus Pic or napropamide. Injury caused by S-metolachlor was transient and plants fully recovered by 4 weeks after treatment (WAT). Yellow nutsedge control 6 WAT using DMDS plus Pic applied at 468 or 560 L ha−1 controlled yellow nutsedge 91 to 95%. Large crabgrass control 6 WAT was 92 to 100% when DMDS plus Pic was applied at 468 or 560 L ha−1 with or without a(n) herbicide (S-metolachlor or napropamide). Palmer Amaranth control prior to harvest was 21, 64, and 85% using DMDS plus Pic at 374, 468, or 560 L ha−1, respectively. DMDS plus Pic applied at 468 or 560 L ha-1 with napropamide followed by S-metolachlor POST gave 95 to 99% control of Palmer amaranth 6 WAT. Consistent weed control and optimum yields were obtained when DMDS plus Pic was used at 468 L ha−1 plus napropamide beneath plastic mulch followed by S-metolachlor POST.

Artilleryweed is an annual or short-lived perennial weed that is becoming increasingly problematic in nurseries and landscapes in tropical and subtropical environments. Currently, no herbicide recommendations exist for management of artilleryweed. Objectives of this trial were to evaluate PRE and POST herbicides for efficacy on artilleryweed. All studies were conducted in Apopka, FL in a shaded greenhouse. Herbicides evaluated for POST control included diquat, dimethenamid-P, flumioxazin, glufosinate, glyphosate, indaziflam, oxadiazon, pelargonic acid, sulfentrazone and sulfosulfuron applied at their highest labelled rates to mature (10 to 12 cm height) artilleryweed. For PRE experiments, pots were overseeded with artilleryweed seed and treated with dimethenamid-P, indaziflam, isoxaben, oxadiazon, oxyfluorfen+prodiamine, oxyfluorfen+pendimethalin, pendimethalin, pendimethalin+dimethenamid-P, prodiamine, prodiamine+isoxaben, S-metolachlor, or trifluralin+isoxaben. When assessing both initial fresh weight and regrowth, flumioxazin and glufosinate provided the most consistent POST control when applied at the highest labelled rate, although regrowth did occur following application with glufosinate. All PRE herbicides evaluated provided over 90% control of artilleryweed with the exception of isoxaben and trifluralin+isoxaben. Results indicate that several effective options exist for artilleryweed management, but more effective control will likely be achieved when herbicides are applied PRE.

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.

Metribuzin will control many problematic weed species in winter wheat in the mid-Atlantic states, including herbicide-resistant biotypes, but it has not been recommended due to crop safety concerns. In a three-year trial, metribuzin was applied at 105 or 210 g ai ha−1 to wheat at the PRE, 2-leaf (Feekes stage 1 to 2), early spring (Feekes stage 3 to 4), and late spring (Feekes stage 4 to 6) growth stages using wheat cultivars sensitive to metribuzin. Early spring applications had the least amount of injury, and injury at this timing was transient and yield was not reduced. Yield loss was observed with the other application timings in at least one out of three years. Rainfall shortly after application appears to increase the risk of wheat injury.

Annual bluegrass seedhead suppression on golf greens by spring-applied plant growth regulators (PGR) has been erratic between years and locations. To effectively suppress annual bluegrass seedheads on greens, current information suggest ethephon must be applied before floral initiation. Rogue seedheads, however, can sometimes be found in late winter indicating that a variable proportion of annual bluegrass plants may induce floral initiation in winter. Studies were conducted in Blacksburg and Harrisonburg, VA at five separate sites between 2011 and 2012 to determine if winter applications of ethephon or mefluidide would improve annual bluegrass seedhead suppression when applied in advance of a spring, two-treatment program. A spring, two-treatment program of ethephon plus trinexapac-ethyl reduced annual bluegrass seedhead cover 22 to 55% depending on trial and less than similar mefluidide programs. Applying an early application of ethephon in January or February prior to the spring treatment program resulted in 5 to 7 times less seedhead cover at cover maxima than the spring treatment program alone. Ethephon did not injure creeping bentgrass and caused only slight and transient discoloration to annual bluegrass. Mefluidide injured both creeping bentgrass and annual bluegrass and reduced annual bluegrass population density in late spring. Programs that consisted of an early ethephon application, a spring treatment of triademifon, and two spring treatments of ethephon plus trinexapac ethyl improved seedhead suppression and turf quality but slightly increased annual bluegrass injury. Methiozolin suppressed annual bluegrass seedheads primarily through severe injury to annual bluegrass, which led to a decline in turfgrass quality and NDVI but a substantial increase in creeping bentgrass cover. Applying PGRs in winter is a novel concept and may substantially improve ethephon consistency and performance for annual bluegrass seedhead suppression on greens.

If registered for use on vegetable soybean, pyroxasulfone would expand the options for weed management systems in the crop. In order to determine the potential crop injury risk of pyroxasulfone on vegetable soybean, the objective of this work was to quantify vegetable soybean tolerance to pyroxasulfone applied PRE and EPOST. Twenty-one vegetable soybean and two grain-type soybean cultivars were treated with pyroxasulfone at 417 gaiha−1 (twice the recommended field use rate) PRE, EPOST, or not treated. Plant population density was unaffected by pyroxasulfone. Only low levels (<10%) of crop injury were observed within a few weeks after PRE and EPOST treatments. Soybean cultivars were not differentially affected by pyroxasulfone, as evidenced by the lack of interactions between cultivar and treatment for any crop response variable. The low amount of risk of crop injury associated with pyroxasulfone is no different for vegetable soybean cultivars grown in the US for commercial production than grain-type soybean.

Sheep and hair fescue are perennial, tuft forming grasses that spread by seed and form dense sods in wild blueberry fields. These sods compete with the crop for resources and hinder harvest. Field and greenhouse studies were conducted in 2015 to evaluate 1) the effect of sequential glufosinate and foramsulfuron applications on suppression of fescues in the greenhouse and field, and 2) efficacy of glufosinate and foramsulfuron on fescue seedlings when applied at 2, 4, 6, and 8 wk after seedling emergence in the greenhouse. Glufosinate applications at 750 and 1,005 g ai ha−1 followed by foramsulfuron application at 35 g ai ha−1 reduced fescue leaf number and biomass relative to foramsulfuron application alone in the greenhouse. In the field study, fescue flowering tuft density, tuft inflorescence height, seed production, and seed viability were reduced by foramsulfuron alone, but there was a trend towards lower seed production and tuft height when fescues were treated with glufosinate at 1,005 g ha−1 followed by foramsulfuron. Foramsulfuron caused low seedling mortality at all application timings evaluated, but glufosinate caused >90% mortality in seedlings when applied at 2, 4, 6, or 8 wk after seedling emergence. Our results suggest that sequential applications of these herbicides are less effective under field conditions relative to results obtained in the greenhouse, though burndown glufosinate applications may have a role in reducing fescue seedling recruitment. Additional research should be conducted to determine the effect of early spring and autumn glufosinate applications on fescue seedling recruitment and suppression of established fescue tufts with subsequent foramsulfuron applications.

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.

Doveweed is a problematic weed of lawns and sod production, as well as golf course roughs, fairways, and tees. End-user reports of selective POST control options are inconsistent and control is often short-lived. In addition, inconsistent control with non-selective herbicides such as glyphosate is common. The goals of this research were: (1) evaluate selective POST doveweed control options in ‘Tifway’ hybrid bermudagrass turf; (2) compare efficacy of single vs. sequential applications of selective POST herbicides; (3) quantify doveweed tolerance to glyphosate; and (4) quantify recovery of foliar applied glyphosate following treatment with a C14-glyphosate solution. A single application of sulfentrazone+metsulfuron; thiencarbazone+iodosulfuron+dicamba or 2,4-D+MCPP+dicamba+carfentrazone; or thiencarbazone+foramsulfuron+halosulfuron provided >60% control 2 weeks after initial treatment (WAIT). A second application of these treatments 3 WAIT improved control 6 WAIT. Two applications of 2,4-D+MCPP+dicamba+carfentrazone or thiencarbazone+foramsulfuron+halosulfuron provided ~80% control 6 WAIT. Doveweed was tolerant to glyphosate application up to 5.68 kgaeha-1. Absorption of 14C-glyphosate was compared between doveweed with cuticle intact, doveweed with a disturbed cuticle, and smooth crabgrass. 14C-glyphosate recovery from the leaf surface of doveweed plants with an intact cuticle was 93.6%. In comparison, 14C-glyphosate recovery from the leaf surface of doveweed plants with a disrupted cuticle and the leaf surface of crabgrass plants was 79.1 and 70.5%, respectively.

Two populations of southern crabgrass identified in Georgia turfgrass were suspected to be resistant to sethoxydim. The objectives of this research were to evaluate the resistance levels of these biotypes to acetyl-CoA carboxylase (ACCase) inhibitors and alternative herbicides for control. From dose response experiments, the sethoxydim rate required to reduce shoot biomass 50% from the nontreated measured >64-times greater for both resistant (R) biotypes compared to the susceptible (S) biotype. Both R biotypes were cross-resistant to fenoxaprop and fluazifop. Clethodim at 290 gaiha−1 reduced dry shoot biomass of the R biotypes and the S biotype to 47 and 21% of the nontreated, respectively. The R biotypes were equally susceptible to MSMA at 2240 g ai ha−1, quinclorac at 840 g ai ha−1, and topramezone at 37 g ai ha−1 as compared to the S biotype. Sethoxydim at 315 and 945 g ha−1 provided <20% control of the southern crabgrass populations in four field experiments. However, clethodim and topramezone provided 83% and 76% control at 4 wks after treatment, respectively. These southern crabgrass biotypes are resistant to sethoxydim and aryloxyphenoxypropionate herbicides. Although the R biotypes were less susceptible to clethodim than the S biotype, treatments provided acceptable control in the field. This is the first report of ACCase-resistant southern crabgrass in the United States.