A major hindrance to establishment of successful complementary forage systems that include warm-season perennial grasses and clovers is tolerance of the latter to herbicides available for weed control. Field experiments were conducted in 2013 at two locations in northeast Louisiana to evaluate simulated residual rate effects of fluroxypyr plus triclopyr and 2,4-D plus picloram applied at 0, 0.25, 0.38, and 0.5× use rates immediately after fall planting of ball, white, crimson, and red clover. For all clovers, when averaged across herbicide rates, plant population 161/171 d after planting (DAP), ground cover, and height 184/196 DAP were equivalent for fluroxypyr plus triclopyr and the nontreated control and greater than 2,4-D plus picloram. Averaged across clovers, plant height after all rates of fluroxypyr plus triclopyr was equivalent to the nontreated control (14.2 to 14.3 vs. 15.3 cm) and greater than 2,4-D plus picloram. Compared with the nontreated control, 2,4-D plus picloram at 25, 38, and 50% of the normal use rates reduced height 58, 76, and 85%, respectively. When averaged across clover species, yield for fluroxypyr plus triclopyr at all rates was equivalent to the nontreated control (2,624 to 2,840 vs. 2,812 kg ha−1). Compared with the nontreated control, 2,4-D plus picloram at the 0.25, 0.38, and 0.50× use rates reduced yield 65, 89, and 99%, respectively.

Field studies were conducted near Crowley, LA, to evaluate the effects of simulated herbicide drift on ‘Cocodrie' rice. Each treatment was made with the spray volume varying proportionally to herbicide dosage based on a spray volume of 234 L ha−1 and an imazamox rate of 44 g ai ha−1. The 6.3%, 2.7-g ha−1, herbicide rate was applied at a spray volume of 15 L ha−1 and the 12.5%, 5.5-g ha−1, herbicide rate was applied at a spray volume of 29 L ha−1. Rice was treated at the one-tiller, panicle differentiation, boot, and physiological maturity growth stages. Injury was observed with imazamox applied at the one-tiller timing. Injury was not observed until 21 and 28 d after treatment (DAT) when imazamox was applied at the panicle differentiation and boot timings. The greatest reduction in plant height resulted from applications at the one-tiller timing at 7 and 14 DAT; however, when evaluated at harvest, plant height was reduced no more than 10%. Imazamox, averaged over rate, applied to rice at the boot timing reduced primary crop yield 66% compared with the nontreated. Applications at the boot timing resulted in an increased ratoon crop yield; however, the yield increase did not compensate for the loss in the primary crop yield.

Although primarily used as an effective PRE herbicide, indaziflam has been shown to provide early POST control of some weeds commonly found in nursery production. Previous investigation on the early POST efficacy of indaziflam focused on the liquid formulation, and the ability of the granular formulation to provide early POST weed control is unknown. Nursery trials were conducted to evaluate early POST control of oxalis using two formulations of indaziflam. Oxalis seeds were surface sown to nursery containers at two separate dates and grown until they reached the two- to four-leaf stage (2-4L) and six- to eight-leaf stage. Both growth stages were treated with indaziflam at 12.6, 25.1, 50.2, and 100.4 g ai ha−1 using either a granular (G) or liquid (SC) formulation. A chemical control treatment (glyphosate) and a nontreated control were also included for comparison. The SC formulation provided > 90% control of both oxalis growth stages at all four rates and was similar to glyphosate. The G formulation at 12.6 and 25.1 g ha−1 only provided marginal control, but overall performed similarly to the SC formulation at the 50.2 and 100.4 g ha−1 rate in most experiments. In contrast to the SC formulation, the G formulation is labeled for use over the top of container-grown nursery crops. Results of this research indicate that in areas where oxalis is the primary weed of concern, the G formulation of indaziflam could be applied to control small oxalis up to the 2-4L stage at the currently labeled rate (50.2 g ha−1).

Smooth barley is an annual weed species that is infesting crops and pastures in South Australia. Complicating control options is the presence of herbicide-resistant biotypes. A field trial was conducted to identify alternative herbicides for the management of acetyl coenzyme A carboxylase (ACCase)-inhibiting herbicide-resistant smooth barley in field pea. Preplant (PP) soil applications of pyroxasulfone; prosulfocarb plus S-metolachlor; dimethenamid-P; propyzamide; trifluralin alone or with triallate or with diuron; or imazamox applied POST were evaluated for their effectiveness and crop safety. Propyzamide, pyroxasulfone, or imazamox applied POST provided a high level of smooth barley control, did not cause any crop injury, and increased field pea grain or forage yield compared with the nontreated. Furthermore, propyzamide or pyroxasulfone reduced panicle density and seed production in smooth barley, whereas the effectiveness of POST imazamox varied over the two seasons. Dimethenamid-P reduced the impact of smooth barley on field pea yield, but cause stunting, and was less effective than propyzamide, pyroxasulfone, and imazamox in reducing smooth barley seed production. Negative relationship between field pea yield and smooth barley panicle density indicated that smooth barley is highly competitive in field pea crops and can cause large yield losses. The results of this investigation suggest that propyzamide or pyroxasulfone applied PP and imazamox applied POST could be used effectively in the field for the management of ACCase-inhibiting herbicide-resistant smooth barley in South Australia.

Volunteer corn can affect dry bean by reducing yields; expanding the life cycle of insects, mites, and pathogens; interfering with harvest; and contaminating bean seed. Field studies were conducted at Lingle, WY, and Scottsbluff, NE, to determine the relationship between volunteer corn density and dry bean yield, establish the proper time of volunteer corn removal, and determine whether dry bean yield was affected by the method used to remove volunteer corn. Volunteer corn reduced dry bean yields, as recorded in other crops. Growing conditions for each location were different, as indicated by the accumulated growing degree days (GDD): Lingle 2008 (990), Lingle 2009 (780), and Scottsbluff 2009 (957). No difference in dry bean yields was observed between hand removal of volunteer corn and herbicide application. Dry bean yield loss increased with longer periods of volunteer corn competition and ranged from 1.2 to 1.8% yield loss for every 100 GDD that control was delayed. Control measures should be implemented 15 to 20 d after planting when volunteer corn densities are close to 1 plant m−2. Dry bean yield losses also increased as volunteer corn densities increased, with losses from 6.5 to 19.3% for 1 volunteer corn plant m−2. Based on 2015 prices, the cost of controlling volunteer corn would be the equivalent of 102 kg ha−1 of dry bean, and potential losses above 4% would justify control and should not be delayed beyond 15 to 20 d after planting.

Lentil is vulnerable to weed competition because of its short stature, slow establishment, and limited vegetative growth. Although the vast majority of lentil production is under rain-fed conditions, there is a little published information on weed control with herbicides in rain-fed lentils. Field experiments were conducted to determine the efficacy of nine herbicide treatments including fomesafen, imazethapyr, linuron, pendimethalin, and pyridate alone or in combination compared with one or two hand weeding(s) on weed control and yield response in rain-fed lentil in Khorramabad, Iran in 2012 and 2013. Weed species included catchweed bedstraw, cowcockle, haresear mustard, hoary cress, wild mustard, and wild safflower. Total weed dry biomass in weedy check plots averaged 156 and 170 g m−2 in 2012 and 2013, respectively, and weed density and biomass were reduced in all treatments compared to the weedy check in both years. Plots that were hand weeded twice reduced weed biomass the greatest, whereas fomesafen, linuron, or one hand weeding did not control weeds satisfactorily. Noncontrolled weeds reduced lentil yield by 67% both years compared to the weed-free control. Lentil yield in 2013 (1,370 kg ha−1) was higher than in 2012 (1,150 kg ha−1). All herbicides tested injured lentil slightly, with pyridate (1,200 g ai ha−1) and pendimethalin (660 g ai ha−1 plus imazethapyr at 250 to 500 g ai ha−1) causing the least injury. Across all treatments, imazethapyr plus pendimethalin PRE, pyridate POST, and two hand-weeding treatments had the best performance for weed control and lentil yield.

Field and greenhouse experiments were conducted to characterize the response of a waterhemp population from McLean County, IL to foliar-applied 4-hydroxyphenylpyruvate dioxygenase (HPPD) –inhibiting herbicides and determine the population's sensitivity to herbicides from other site-of-action groups. In the field, 10 to 15–cm-tall waterhemp treated with mesotrione at 105 g ai ha−1, tembotrione at 92 g ai ha−1, or topromezone at 18 g ai ha−1 had significantly greater biomass (≥ 10%) 14 d after treatment (DAT) than waterhemp harvested the day of herbicide application, indicating growth had occurred following herbicide application. Waterhemp growth stage at the time of herbicide application influenced control. Mesotrione applied at 105 g ha−1 alone or combined with atrazine at 560 g ai ha−1 provided significantly greater waterhemp control (≥ 66%) when applied to small waterhemp plants (2 to 5 cm tall) compared with applications made to plants 5 to 10 or 10 to 15 cm tall. Glyphosate, glufosinate, fomesafen, lactofen, or acifluorfen provided greater waterhemp control (≥ 68%) 7 and 14 DAT than mesotrione, dicamba, or 2,4-D. Control of this population with atrazine, chlorimuron, and imazethapyr did not exceed 12%. Results of a greenhouse experiment with waterhemp plants grown from field-collected seed were similar to field data, and confirm the McLean County population was poorly controlled with HPPD, photosystem II, and acetolactate synthase inhibitors.

Field bindweed is a deep-rooted and drought-tolerant perennial that can be difficult to control once it has become established in specialty crops. Field studies were conducted in 2013 and 2014 to evaluate the efficacy of currently registered preplant (PP), PPI, PRE, and POST herbicides for field bindweed management in both early and late-planted processing tomatoes. Results show that bindweed cover in PPI/PRE programs (trifluralin, alone or in combination with rimsulfuron; S-metolachlor; or sulfentrazone) was reduced > 50% in early planted tomatoes, relative to the no PPI/PRE herbicide treatment (0 to 31% cover at up to 6 wk after transplanting [WAT]). Similar trends were observed with respect to field bindweed density. PP applications of glyphosate to emerged bindweed in late-planted tomatoes, coupled with PPI/PRE herbicide applications, reduced weed cover (1 to 13% at up to 6 WAT) by more than one-half when compared with plots treated with residual herbicides alone (1 to 43% at up to 6 WAT); perennial vine density was also reduced > 50%. PP herbicide burndown applications and the use of residual products can significantly improve the suppression of field bindweed in processing tomato systems. The emergence and vigor of bindweed vines may differ with respect to the timing of transplant operations and should be considered when developing management strategies

Black medic is a troublesome weed in commercial strawberry fields in Florida. It emerges during crop establishment from the planting holes punched in plastic mulches that are installed on raised beds. Clopyralid is registered for posttransplant applications at 140 to 280 g ae ha−1 but growers typically report suppression, not control. An outdoor potted experiment was designed to model the black medic dose-response curve and determine the effect of plant size at application on control. Two plant sizes were selected: designated small (0.5- to 1-cm stem length) and large (3- to 6-cm stem length). Dose-response curves were generated using a log-logistic four-parameter model. At 22 d after treatment (DAT), there was a significant interaction between clopyralid rate and black medic growth stage on both epinasty (P = 0.0022) and chlorosis (P = 0.0055). The effective dosage to induce 90% (ED90) epinasty were 249.5 and 398.3 g ha−1 for the small and large growth stages, respectively. The ED90 for chlorosis was 748.2 for the small growth stage, whereas the estimated value for the large was outside the measured range. For necrosis there was no significant effect of growth stage, and the ED90 was 1,856.3 g ha−1. The aboveground dry biomass ED90 for the small growth stage was 197.3 g ha−1, and the estimated ED90 value for the large was not within the measured range. Results indicate that clopyralid adequately controls black medic when applied at maximum label rates when stems were 0.5 to 1 cm long but not when plants were larger. Poor efficacy typically observed in commercial fields is likely due to black medic plant size or lack of herbicide coverage via shielding by strawberry plants.

In Australia, triazine herbicides have routinely controlled the Vulpia species (Vulpia bromoides, Vulpia myuros, and Vulpia fasciculata; collectively referred to as silvergrass). However, a simazine-resistant silvergrass biotype, collected from Pingelly in the Western Australian grain belt in 2014, has been confirmed. Compared to the pooled mortality of three simazine-susceptible silvergrass populations (S1, S2, and S3), the simazine-resistant Pingelly population was > 594-fold resistant at the LD50 level. Dose-response screening of the simazine-selected progeny (> 800 g ai simazine ha−1) demonstrated that the simazine resistance mechanism was heritable. Sequencing of the chloroplast psbA gene revealed the resistant population is homozygous for a serine 264 to glycine mutation, which confers a high-level triazine resistance. As expected this Ser-264-Gly mutation conferred resistance to atrazine and metribuzin, but not the phenyl-urea diuron. This is the first published report confirming field-evolved triazine resistance in a Vulpia population.

Two varieties of bahiagrass were evaluated under Florida conditions for forage tolerance to the new herbicide, aminocyclopyrachlor (ACP), which is essential for product development decisions. Herbicide treatments included ACP alone at 70 and 140 g ai ha−1, ACP + chlorsulfuron at 69 + 27 and 138 + 54 g ai ha−1, ACP + 2,4-D amine at 70 + 532 g ai ha−1 and 140 + 1,064 g ai ha−1, ACP + triclopyr-amine at 70 + 140 g ai ha−1 and 140 + 280 g ai ha−1, and ACP + metsulfuron at 46 + 7, 78 + 12, and 168 + 26 g ai ha−1, and also included a nontreated check. ‘Argentine’ bahiagrass was the most tolerant forage species, and ‘Pensacola’ bahiagrass was sensitive to ACP + metsulfuron and initially to ACP + chlorsulfuron. Herbicide applications using ACP, when labeled, will likely provide good to excellent control of several weed species, with little long-term impact on bahiagrass forage production when the cultivar is known.

Water is the primary carrier for herbicide application, and carrier-water–related factors can influence herbicide performance. In a greenhouse study, premixed formulation of glyphosate plus dicamba was mixed in deionized (DI) water at 5, 18, 31, 44, or 57 C and applied immediately. In a companion study, glyphosate and dicamba formulation was mixed in DI water at temperatures of 5, 22, 39, or 56 C and sprayed after the herbicide solution was left at the respective temperatures for 0, 6, or 24 h. In both studies, glyphosate plus dicamba was applied at 0.275 plus 0.137 kg ae ha−1 (low rate), and 0.55 plus 0.275 kg ha−1 (high rate), respectively, to giant ragweed, horseweed, Palmer amaranth, and pitted morningglory. Glyphosate plus dicamba applied at a low rate with solution temperature of 31 C provided 14% and 26% greater control of giant ragweed and pitted morningglory, respectively, compared to application at solution temperature of 5 C. At both rates of glyphosate and dicamba formulation, giant ragweed and pitted morningglory control was 15% or greater at solution temperature of 44 C compared to 5 C. Weed control was not affected with premixture of glyphosate and dicamba applied ≤ 24 h after mixing herbicide. When considering solution temperature, glyphosate and dicamba applied at low rate provided 13 and 6% greater control of Palmer amaranth and pitted morningglory, respectively, with solution temperature of 22 C compared to 5 C. Similarly, giant ragweed control was 8% greater with solution temperature of 39 C compared to 5 C. Glyphosate and dicamba applied at high rate provided 8% greater control of giant ragweed at solution temperature of 22 or 39 C compared to 5 C. Therefore, activity of premixed glyphosate and dicamba could be reduced with spray solution at lower temperature; however, the result is dependent on weed species.

Fresh market spinach has one primary herbicide, cycloate, which does not control all weeds. Previous studies demonstrated that cycloate PRE followed by (fb) phenmedipham at the four-leaf spinach stage is a safe and effective treatment. However, this treatment is not useful for the main growing season of fresh spinach due to its short crop cycle and the 21-d preharvest interval requirement of phenmedipham. This study evaluates the potential to use the combination of cycloate PRE fb phenmedipham on two-leaf spinach. Greenhouse and field studies were conducted in 2014 using three spinach varieties with low (‘Nordic' and ‘Sardinia') and high (‘Regal') tolerance to phenmedipham. Greenhouse studies revealed that phenmedipham at 90 g ai ha−1 was safe to Regal when applied at the two-leaf stage. Sardinia was more susceptible to phenmedipham injury under high (310 W m−2) light conditions than low (258 W m−2) light conditions. Impact of time of day on phenmedipham safety was evaluated in the field: day-long exposure to high light intensity following morning applications vs. evening applications fb exposure to low light intensity. Injury estimations taken 3 d after treatment (DAT) were lower for evening than for morning applications. Nonetheless, injury 11 DAT and spinach yield evaluations found no differences between morning and evening applications. Subsequently, cycloate (1,700 g ha−1) PRE fb phenmedipham (90 and 180 g ha−1) applied in the evening at the two-leaf stage was evaluated. A reference treatment was cycloate PRE fb phenmedipham (270 g ha−1) at the four-leaf stage. Treatments with cycloate fb two-leaf phenmedipham at 90 and 180 g ha−1 were safe to spinach and improved weed control compared to cycloate alone. Cycloate fb 180 g ha−1 phenmedipham at the two-leaf stage reduced weed biomass by 88% compared to cycloate alone. This level of weed control was similar to the reference treatment. Results here show that phenmedipham applied at the two-leaf stage is safe to fresh market spinach and it has the potential to be used during most of the fresh spinach growing season.

In plasticulture vegetable production systems, broadleaf weeds and grasses emerge in the crop planting holes and between the raised beds. Weeds emerging on the bare ground between the raised beds can be the most difficult to control. Experiments were conducted in the spring and fall of 2014 at the Gulf Coast Research and Education Center in Balm, FL, to evaluate a range of herbicides for use in row middles in vegetable crops. Weed counts and control ratings did not differ over time and as a result are averaged across 2, 4, and 8 wk after treatment. In the absence of PRE herbicides, carfentrazone did not differ from the nontreated control, whereas paraquat reduced total weed density by 67 and 61% in the spring and fall, respectively. In the fall, carfentrazone tank-mixed with flumioxazin, S-metolachlor + flumioxazin, or paraquat tank-mixed with flumioxazin, S-metolachlor, metribuzin, or S-metolachlor + flumioxazin had 81 to 90% fewer broadleaf weeds than the nontreated control. Total weed density was 70 to 90% lower than the nontreated control when carfentrazone was tank-mixed with flumioxazin or S-metolachlor + flumioxazin or paraquat was tank-mixed with flumioxazin, S-metolachlor, oxyfluorfen, metribuzin or S-metolachlor + flumioxazin. Similar trends occurred in the spring. A tank mix of a soil residual herbicide and POST burn-down herbicides tended to have a greater reduction in weed numbers compared to the POST treatment alone. The most consistent row middle tank-mixes were paraquat tank-mixed with flumioxazin, S-metolachlor + flumioxazin, or S-metolachlor + oxyfluorfen.

Studies were conducted in a stale field production system in 2012 and 2013 to determine the effect of herbicide timing on Palmer amaranth control and ‘Covington’ sweetpotato yield and quality. Treatments consisted of flumioxazin at 72, 90, or 109 g ai ha−1 applied 45 d before transplanting (DBT) or 1 DBT, or sequentially the same rate at 45 DBT followed by (fb) 1 DBT; flumioxazin 109 g ha−1 applied 1 DBT fb S-metolachlor (800 g ai ha−1) at 0, 6 (± 1), or 10 d after treatment (DAT); flumioxazin at 72, 90, or 109 g ha−1 plus clomazone (630 g ai ha−1) applied 45 DBT fb S-metolachlor (800 g ha−1) applied 10 DAT; and fomesafen alone at 280 g ai ha−1 applied 45 DBT. Nontreated weed-free and weedy controls were included for comparison. Flumioxazin application time had a significant effect on Palmer amaranth control and sweetpotato yields, and the effect of flumioxazin rate was not significant. Treatments consisting of sequential application of flumioxazin 45 DBT fb 1 DBT or flumioxazin plus clomazone 45 DBT fb S-metolachlor 10 DAT provided the maximum Palmer amaranth control and sweetpotato yields (jumbo, No. 1, jumbo plus No. 1, marketable) among all treatments. Delayed flumioxazin application timings until 1 DBT allowed Palmer amaranth emergence on stale seedbeds and resulted only in 65, 62, 48, and 17% control at 14, 32, 68, and 109 DAT, respectively. POST transplant S-metolachlor applications following flumioxazin 1 DBT did not improve Palmer amaranth control, because the majority of Palmer amaranth emerged prior to S-metolachlor application. A control program consisting of flumioxazin 109 g ha−1 plus clomazone 630 g ha−1 at 45 DBT fb S-metolachlor 800 g ha−1 at 0 to 10 DAT provides an effective herbicide program for Palmer amaranth control in stale seedbed production systems in North Carolina sweetpotato.

Field experiments were conducted in 2013 and 2014 to determine the influence of velvetleaf densities of 0, 0.125, 0.25, 0.5, 1, 2, 4, and 8 plants m−1 of row on cotton growth and yield. The relationship between velvetleaf density and seed cotton yield was described by the hyperbolic decay regression model, which estimated that a density of 0.44 to 0.48 velvetleaf m−1 of row would result in a seed cotton yield loss of 50%. Velvetleaf remained taller and thicker than cotton throughout the growing season. Both cotton height and stem diameter reduced with increasing velvetleaf density. Moreover, velvetleaf interference delayed cotton maturity, especially at velvetleaf densities of 1 to 8 plants m−1 of row, and cotton boll number and weight, seed numbers per boll, and lint percentage were also reduced. Fiber quality was not influenced by weed density when analyzed over 2 yr; however, fiber length uniformity and micronaire were adversely affected in 2014. Velvetleaf intraspecific competition resulted in density-dependent effects on weed biomass, ranging from 97 to 204 g plant−1 dry weight. Velvetleaf seed production per plant or per square meter was indicated by a logarithmic response. At a density of 1 plant m−1 of cotton row, velvetleaf produced approximately 20,000 seeds m−2. The adverse impact of velvetleaf on cotton growth and development identified in this study have indicated the need for effective management of this species when the weed density is greater than 0.25 to 0.5 plant m−1 of row and before the weed seed maturity.

Recent trends favoring organic and sustainable turfgrass management practices have led to an increased desire for biologically based alternatives to traditional synthetic herbicides. Thaxtomin A, produced by the bacterium Streptomyces scabies, has been reported to have PRE efficacy on broadleaf weeds, but efficacy of thaxtomin A on annual grassy weeds and safety to newly seeded cool-season turfgrasses have not been reported. Field experiments were conducted to evaluate PRE efficacy of thaxtomin A on smooth crabgrass and annual bluegrass. Monthly applications of thaxtomin A from April to July controlled smooth crabgrass through July but did not provide season-long control equivalent to an industry standard PRE herbicide. An initial application of thaxtomin A at 380 g ai ha−1 followed by two applications at 190 or 380 g ha−1 at 4-wk intervals provided season-long annual bluegrass control similar to an industry standard PRE herbicide. At 380 g ha−1, thaxtomin A reduced tall fescue and perennial ryegrass cover when applied 1 wk before seeding, at seeding, or 1 wk after seeding but was safe at other application timings. Up to three applications of thaxtomin A at 380 g ha−1 at 4-wk intervals did not reduce perennial ryegrass cover. Applications to creeping bentgrass resulted in unacceptable turfgrass injury. These results suggest that thaxtomin A can suppress annual grassy weeds in tall fescue or perennial ryegrass turf when applied at least 2 wk before or after seeding. Furthermore, repeated applications of thaxtomin A can provide effective PRE control of annual bluegrass during overseeded perennial ryegrass establishment.

Two experiments were conducted in 2015 at multiple locations in Florida to evaluate the effects of planting depth and application timing on S-metolachlor injury in sesame. In both studies, sesame responded negatively to increases in S-metolachlor rate. Altering sesame planting depth did not provide increased safety to PRE S-metolachlor applications. Sesame establishment declined with increased planting depth, likely because of the physical inability of the small seed to emerge from the 3.8-cm depth. Delaying applications of S-metolachlor by 3 or 6 d after planting (DAP) consistently improved sesame establishment. Applications 3 and 6 DAP resulted in 89 to 92% seedling emergence at 2 wk after planting (WAP), relative to 55 to 63% emergence when S-metolachlor was applied the day of planting (0 DAP) or 3 days before (−3 DAP), respectively. Applications 3 DAP resulted in 21 and 2% plant stunting when evaluated 3 and 6 WAP, respectively, whereas all other timings caused 25 to 51% stunting. Yield was reduced 22 and 33% by the −3 DAP and 0 DAP application timings, respectively, whereas no reduction in yield was observed by the delayed application timings. Therefore, delaying applications of S-metolachlor by 3 to 6 days will likely result in improved sesame seedling establishment and total seed yield.

Because horsenettle and tall ironweed are difficult to control in cool-season grass pastures, research was conducted in Tennessee and Kentucky in 2010 and 2011 to examine the efficacy of aminocyclopyrachlor on these weeds. Aminocyclopyrachlor was evaluated at 49 and 98 g ai ha−1 alone and in mixtures with 2,4-D amine at 371 and 742 g ae ha−1. Aminopyralid was also included as a comparison treatment at 88 g ai ha−1. Treatments were applied at three POST timings to horsenettle and two POST timings to tall ironweed. By 1 yr after treatment (YAT) horsenettle was controlled 74% with aminocyclopyrachlor plus 2,4-D applied late POST (LPOST) at 98 + 742 g ha−1. By 1 YAT, tall ironweed was controlled ≥ 93% by aminocyclopyrachlor applied early POST (EPOST) or LPOST, at rates as low as 49 g ha−1. Similar control was achieved with aminopyralid applied LPOST. Both aminocyclopyrachlor and aminopyralid were found to reduce horsenettle and tall ironweed biomass the following year. Moreover, all LPOST applications of aminocyclopyrachlor alone or in mixtures with 2,4-D prevented regrowth of tall ironweed at 1 YAT. Based on these studies, a LPOST herbicide application in August or September when soil moisture is adequate is recommended for control of horsenettle and tall ironweed in cool-season grass pastures.

Field experiments were conducted from 2011 to 2013 near Ridgetown and Exeter, Ontario, Canada to evaluate the tolerance of seven identity-preserved (IP) soybean cultivars to protoporphyrinogen oxidase (PPO)-inhibiting herbicides flumioxazin, saflufenacil/dimethenamid-P, and sulfentrazone applied PRE; fomesafen applied POST; as well as PRE followed by (fb) POST application. Ridgetown sites demonstrated excellent tolerance (< 10% injury) to PRE treatments, whereas PRE sulfentrazone caused up to 36% injury at 1 and 2 wk after application (WAA) at Exeter. Of the PRE fb POST treatments evaluated, those containing saflufenacil/dimethenamid-P and sulfentrazone were most injurious to soybean, with cultivar being a further determinant of injury. At Exeter 1 WAA, cultivars ‘S03W4’ and ‘S23T5’ showed 23 to 27 and 45 to 46% injury for saflufenacil/dimethenamid-P and sulfentrazone when followed by POST fomesafen, respectively. Sulfentrazone application (PRE alone or fb fomesafen) consequently reduced S03W4 yield up to 38% and S23T5 up to 25%, whereas saflufenacil/dimethenamid-P fb fomesafen reduced S03W4 by 18%. In general, PRE fb POST caused more injury than PRE treatments; however, injury diminished over time and no significant reduction to soybean yield could be attributed to adding POST fomesafen. On the basis of this study, the injury from PPO herbicides applied PRE is active ingredient, cultivar, and environment specific. Although PPO herbicides have the potential to cause unacceptable crop injury in some IP soybean cultivars, selecting a tolerant cultivar will minimize yield losses.