Foliar applied postemergence herbicides are a critical component of corn and soybean weed management programs in North America. Rainfall and air temperature around the time of application may affect the efficacy of herbicides applied postemergence in corn or soybean production fields. However, previous research utilized a limited number of site-years and may not capture the range of rainfall and air temperatures that these herbicides are exposed to throughout North America. The objective of this research was to model the probability of achieving successful weed control (≥85%) with commonly applied postemergence herbicides across a broad range of environments. A large database of over 10,000 individual herbicide evaluation field trials conducted throughout North America was used in this study. The database was filtered to include only trials with a single postemergence application of fomesafen, glyphosate, mesotrione, or fomesafen + glyphosate. Waterhemp (Amaranthus tuburculatus (Moq.) J. D. Sauer), morningglory species (Ipomoea spp.), and giant foxtail (Setaria faberi Herrm.) were the weeds of focus. Separate random forest models were created for each weed species by herbicide combination. The probability of successful weed control deteriorated when the average air temperature within the first ten d after application was <19 or >25 C for most of the herbicide by weed species models. Additionally, dryer conditions prior to postemergence herbicide application reduced the probability of successful control for several of the herbicide by weed species models. As air temperatures increase and rainfall becomes more variable, weed control with many of the commonly used postemergence herbicides is likely to become less reliable.

Weeds belonging to the Amaranthus family are most problematic for soybean producers. With Palmer amaranth evolving resistance to multiple herbicides labeled for use in soybean, producers seek new sites of action to integrate into season-long herbicide programs. Bayer CropScience plans to launch a Convintro™ brand of herbicides, one being a premixture that will include diflufenican (WSSA Group 12), metribuzin (WSSA Group 5), and flufenacet (WSSA Group 15), for use preemergence (PRE) in soybean. Research trials were conducted in Fayetteville and Keiser, AR, and Holt, MI, in 2022 and 2023 to evaluate the premixture in a season-long program in a dicamba-resistant soybean system. A 0.17:0.35:0.48 of the diflufenican:metribuzin:flufenacet (DFF-containing) premixture was applied PRE with different combinations of glyphosate, glufosinate, dicamba, and acetochlor at 28 [early-postemergence (EPOST)] and 42 [late-postemergence (LPOST)] days after planting (DAP). At the EPOST timing, the DFF-containing premixture provided >90% Palmer amaranth and prickly sida control. However, common ragweed, common lambsquarters, morningglory ssp., and annual grass control was ≤80% at this timing. When the LPOST applications occurred, treatments that had already received an EPOST application controlled prickly sida, morningglory ssp., Palmer amaranth, and annual grasses greater than those that had not, indicating the PRE application of the DFF-containing premixture was not sufficient to provide control of the weed spectrum through 42 days after planting. By 70 days after planting, all programs provided ≥93% control of all weeds evaluated. Herbicide programs that utilized the DFF-containing premixture PRE fb EPOST fb LPOST controlled common ragweed, common lambsquarters, morningglory ssp., and annual grasses greater than the one pass postemergence systems. In addition, all herbicide programs evaluated reduced Palmer amaranth seed production by >99%. However, producers that plan to utilize the DFF-containing premixture may need two postemergence herbicide applications to obtain high levels of weed control throughout the growing season.

Khakiweed is a perennial broadleaf weed that is difficult to control because of its multiple means of reproduction, vigorous growth, and deep taproot. Khakiweed reduces the performance of pasture, pecan, and turf areas by choking out desirable grass and legume species. Because information on the effectiveness of contact and residual herbicides for control in pecan and pasture areas is limited, greenhouse studies were conducted to determine the effect of application timing, mode of action, and rate on khakiweed control. Preemergence and postemergence herbicides were applied to mature khakiweed plants at 0.25X, 0.5X, 1X, or 2X the label recommended rate for general broadleaf control. Biomass was collected 3 wk after application. Plants regrew from roots in the greenhouse until a second biomass harvest was collected at 6 wk after treatment (WAT). Metsulfuron-methyl, indaziflam, or pendimethalin was applied preemergence to the soil surface. All rates of preemergence herbicides provided high-efficacy control of regrowth (>85%) compared to the nontreated control. The efficacies of postemergence-applied metsulfuron-methyl, metsulfuron-methyl + nicosulfuron, indaziflam, aminopyralid + florpyrauxifen-benzyl, 2,4-D amine, and 2,4-D amine + florpyrauxifen-benzyl were also examined. All postemergence herbicide treatments exhibited control compared to the nontreated plants at both sample timings (3 and 6 WAT) and increased with herbicide application rate. No herbicide provided high-efficacy control during the initial postspray period (0 to 3 WAT). During the regrowth period (3 to 6 WAT), metsulfuron-methyl alone and in combination gave >85% control of khakiweed biomass, indicating that the sulfonylurea herbicides used in this study are well suited to controlling khakiweed.

Ethofumesate is a broad-spectrum, soil-applied herbicide used to control broadleaf and grass weeds in sugarbeet crops. Ethofumesate is commonly applied preemergence at rates ranging from 1.25 to 4.2 kg ai ha−1, or applied postemergence (POST), up to 0.38 kg ai ha−1. The Generic Crop Science company has developed a new Ethofumesate 4SC label that has increased ethofumesate POST rates up to 4.48 kg ha−1 in sugarbeet with more than two true leaves per plant. Field and greenhouse experiments were conducted in 2018 and 2019 to evaluate sugarbeet tolerance and herbicide efficacy. Field tolerance experiments indicated sugarbeet stature from ethofumesate applied POST at 0.28, 0.56, and 1.12 kg ha−1 was the same as that of the nontreated control, but ethofumesate at 2.24 kg ha−1 reduced sugarbeet stature, although that rate did not affect yield components. Ethofumesate applied POST at 4.48 kg ha−1 reduced sugarbeet stature and affected sugarbeet yield components. Ethofumesate applied alone POST provided weed control of up to 85%, 76%, and 84% on common lambsquarters, redroot pigweed, and waterhemp, respectively, in field efficacy experiments. Mixing ethofumesate at 1.12 kg ha−1 with glyphosate does not provide a second effective herbicide for POST control of common lambsquarters or redroot pigweed, but it does provide residual control of these weeds when at least one-half inch of penetrating rainfall occurs, following application. In greenhouse experiments, ethofumesate alone or ethofumesate plus glyphosate applied to common lambsquarters, redroot pigweed, or waterhemp at heights of less than 2.5 cm provided the best combination of burndown and soil residual control compared with weeds that were 2.5 to 5 cm tall. Ethofumesate applied POST at 1.12 kg ha−1 plus glyphosate provided the best combination of tolerance and efficacy, especially on waterhemp.

Asiatic dayflower (Commelina communis L.) is becoming increasingly invasive in Christmas tree plantations in the U.S. Northeast. Response of C. communis to preemergence or postemergence herbicides was evaluated in separate field and greenhouse experiments. The preemergence herbicides consisted of two application rates of flumioxazin (215 and 429 g ai ha−1), hexazinone plus sulfometuron-methyl (316 and 527 g ai ha−1), indaziflam (41 and 82 g ai ha−1), and S-metolachlor (2,136 and 4,272 g ai ha−1). The postemergence herbicides were: bentazon at 1,121 g ai ha−1, clopyralid at 280 g ae ha−1, mesotrione at 526 g ai ha−1, topramezone at 294 g ai ha−1, and triclopyr at 842 g ae ha−1. At 16 wk after treatment, higher rates of flumioxazin (429 g ha−1), hexazinone plus sulfometuron-methyl (527 g ha−1), indaziflam (82 g ha−1), and S-metolachlor (4,272 ha−1) provided 80% to 92% control and reduced C. communis plant density by 84% to 93% compared with the nontreated control. The lower rates of flumioxazin (215 g ha−1), hexazinone plus sulfometuron-methyl (316 g ha−1), and S-metolachlor (2,136 ha−1) gave 65% to 72% control and reduced C. communis plant density by 27% to 75% compared with the nontreated control. The postemergence application of mesotrione at 526 g ha−1, topramezone at 294 g ha−1, and triclopyr at 842 g ha−1 resulted in 76% to 90% control and reduction in dry biomass of 10- to 12-leaf C. communis at 28 d after treatment. Bentazon at 1,121 g ha−1 and clopyralid at 280 g ha−1 applied postemergence were ineffective with <10% control and reduction in C. communis dry biomass. This study showed that C. communis can be managed effectively with currently registered preemergence and postemergence herbicides in Christmas trees.

Field bindweed is a perennial vining weed with vigorous growth, and is commonly found in highbush blueberry fields of Oregon. It requires and integrated strategy using multiple applications of postemergence herbicides and hand weeding for adequate control. Quinclorac is a herbicide that has been shown to control field bindweed, but no information is available indicating the tolerance of blueberry to quinclorac. The objective of this study was to evaluate the response of blueberry to quinclorac and to evaluate field bindweed control with quinclorac in different mixtures. Three groups of field studies were designed to assess 1) single application control of field bindweed, 2) use of sequential treatments to control field bindweed, and 3) long-term impact of quinclorac on field bindweed. In the single application control studies, a single application of quinclorac at 210 or 420 g ai ha−1 alone or in a mixture with rimsulfuron (35 g ai ha−1) or carfentrazone (35 g ai ha−1), controlled field bindweed by 69% to 76% while reducing its biomass between 22% and 44% compared to the nontreated control (61 g m−2). In a sequential treatment study, a single application of quinclorac (420 g ai ha−1) provided 83% to 100% control of field bindweed, outperforming three sequential applications of carfentrazone. In the long-term study, a single application of quinclorac reduced field bindweed biomass by 50% to 82% in 2019 and 62% to 87% in 2020. These results indicate that quinclorac can be safely applied to highbush blueberry plants. Early spring applications of quinclorac to field bindweed will reduce or eliminate the need for subsequent applications later in the season.

A chloroacetamide herbicide by application timing factorial experiment was conducted in 2017 and 2018 in Mississippi to investigate chloroacetamide use in a dicamba-based Palmer amaranth management program in cotton production. Herbicides used were S-metolachlor or acetochlor, and application timings were preemergence, preemergence followed by (fb) early postemergence, preemergence fb late postemergence, early postemergence alone, late postemergence alone, and early postemergence fb late postemergence. Dicamba was included in all preemergence applications, and dicamba plus glyphosate was included with all postemergence applications. Differences in cotton and weed response due to chloroacetamide type were minimal, and cotton injury at 14 d after late postemergence application was less than 10% for all application timings. Late-season weed control was reduced up to 30% and 53% if chloroacetamide application occurred preemergence or late postemergence only, respectively. Late-season weed densities were minimized if multiple applications were used instead of a single application. Cotton height was reduced by up to 23% if a single application was made late postemergence relative to other application timings. Chloroacetamide application at any timing except preemergence alone minimized late-season weed biomass. Yield was maximized by any treatment involving multiple applications or early postemergence alone, whereas applications preemergence or late postemergence alone resulted in up to 56% and 27% yield losses, respectively. While no yield loss was reported by delaying the first of sequential applications until early postemergence, forgoing a preemergence application is not advisable given the multiple factors that may delay timely postemergence applications such as inclement weather.

In Bangladesh, weeds in transplanted rice are largely controlled by labor-intensive and costly manual weeding, resulting in inadequate and untimely weed control. Labor scarcity coupled with intensive rice production has triggered increased use of herbicides. These factors warrant a cost-effective and strategic integrated weed management (IWM) approach. On-farm trials with transplanted rice were conducted during monsoon (‘Aman’) season in 2016 and 2017 and winter (‘Boro’) season in 2016 to 2017 in agroecological zones 11 and 12 with ten treatments—seven herbicide-based IWM options, one mechanical weed control-based option, and two checks (farmers’ current weed control practice and weed-free)—to assess effects on weed control, grain yield, labor use, and profitability. Compared to farmers’ practice, herbicide-based IWM options with mefenacet + bensulfuron-methyl as preemergence followed by (fb) either bispyribac-sodium or penoxsulam as postemergence fb one hand-weeding were the most profitable alternatives, with reductions in labor requirement by 11 to 25 person-days ha–1 and in total weed control cost by US$44 to 94 ha–1, resulting in net returns increases by US$54 to 77 ha–1 without compromising on grain yield. In contrast, IWM options with bispyrbac-sodium or penoxsulam as postemergence application fb one hand-weeding reduced yields by 12% to 13% and profits by US$71 to 190 ha–1. The nonchemical option with mechanical weeding fb one hand-weeding performed similarly to farmers’ practice on yield and profitability. We suggest additional research to develop feasible herbicide-free approaches to weed management in transplanted rice that can offer competitive advantages to current practices.

Establishment of alfalfa by interseeding it with corn planted for silage can enhance crop productivity but weed management is a challenge to adoption of the practice. Although a simple and effective approach to weed management would be to apply a glyphosate-based herbicide, concerns about herbicide resistance and limitations in available alfalfa varieties exist. Field experiments were conducted to compare the efficacy and selectivity of PRE, POST, and PRE followed by POST herbicide programs to a glyphosate-only strategy when interseeding alfalfa with corn. Experiment 1 compared PRE applications of acetochlor, mesotrione, S-metalochlor, metribuzin, and flumetsulam. Results indicate that acetochlor and metribuzin, and S-metalochlor used at a rate of 1.1 kg ai ha−1 were the most effective and selective PRE herbicides 4 wk after treatment (WAT), but each resulted in greater overall weed cover than glyphosate by 8 WAT. Experiment 2 evaluated applications of bentazon, bromoxynil, 2,4-DB, and mesotrione at early and late POST times. Several herbicides used POST exhibited similar effectiveness and selectivity as glyphosate, including early applications of bromoxynil (0.14 kg ai ha−1) and 2,4-DB (0.84 or 1.68 kg ai ha−1), as well as late applications of bromoxynil (0.42 kg ai ha−1), 2,4-DB (0.84 kg ai ha−1), and mesotrione (0.05 or 0.11 kg ai ha−1). A third experiment compared applications of acetochlor PRE, bromoxynil POST, and a combination of acetochlor PRE with bromoxynil POST. All treatments were effective and safe for use in this interseeded system, although interseeded alfalfa provided 65% to 70% weed suppression in corn planted for silage without any herbicide. Herbicide treatments had no observable impacts on corn and alfalfa yields, so weed management was likely of limited economic importance. However, weed competitiveness can vary based on several different factors including weed species, density, and site-specific factors, and so further investigations under different environments and conditions are needed.

Weed control in tree nut orchards is a year-round challenge for growers that is particularly intense during winter through summer as a result of competition and interference with management and harvest operations. A common weed control program consists of an application of a winter PRE and POST herbicide mixture, followed by a desiccation treatment in early spring and before harvest. Because most spring and summer treatments depend on a limited number of foliar-applied herbicides, summer-germinating species and/or herbicide-resistant biotypes become troublesome. Previous research has established effective PRE herbicide programs targeting winter glyphosate-resistant weeds. However, more recently, growers have reported difficulties in controlling several summer-germinating grass weeds with documented or suspected resistance to the spring and summer POST herbicide programs. In this context, research was conducted to evaluate a sequential PRE approach to control winter- and summer-germinating orchard weeds. Eight field experiments were conducted in tree nut orchards to evaluate the efficacy of common winter herbicide programs and a sequential herbicide program for control of a key summer grass weed species. In the sequential-application strategy, three foundational herbicide programs applied in the winter were either mixed with pendimethalin, followed with pendimethalin in March, or applied as a split application of pendimethalin in both winter and spring. Results indicate that the addition of pendimethalin enhanced summer grass weed control throughout the crop growing season by up to 31%. Applying all or part of the pendimethalin in the spring improved control of the summer grass weed junglerice by up to 49%. The lower rate of pendimethalin applied in the spring performed as well as the high rate in the winter, suggesting opportunities for reducing herbicide inputs. Tailoring sequential herbicide programs to address specific weed challenges can be a viable strategy for improving orchard weed control without increasing herbicide use in some situations.

Southern crabgrass [Digitaria ciliaris (Retz.) Koeler] is an annual grass weed that commonly infests turfgrass, roadsides, wastelands, and cropping systems throughout the southeastern United States. Two biotypes of D. ciliaris (R1 and R2) with known resistance to cyclohexanediones (DIMs) and aryloxyphenoxypropionates (FOPs) previously collected from sod production fields in Georgia were compared with a separate susceptible biotype (S) collected from Alabama for the responses to pinoxaden and to explore the possible mechanisms of resistance. Increasing rates of pinoxaden (0.1 to 23.5 kg ha−1) were evaluated for control of R1, R2, and S. The resistant biotypes, R1 and R2, were resistant to pinoxaden relative to S. The S biotype was completely controlled at rates of 11.8 and 23.5 kg ha−1, resulting in no aboveground biomass at 14 d after treatment. Pinoxaden rates at which tiller length and aboveground biomass would be reduced 50% (I50) and 90% (I90) for R1, R2, and S ranged from 7.2 to 13.2 kg ha−1, 6.9 to 8.6 kg ha−1, and 0.7 to 2.1 kg ha−1, respectively, for tiller length, and 7.7 to 10.2 kg ha−1, 7.2 to 7.9 kg ha−1, and 1.6 to 2.3 kg ha−1, respectively, for aboveground biomass. Prior selection pressure from DIM and FOP herbicides could result in the evolution of D. ciliaris cross-resistance to pinoxaden herbicides. Amplification of the carboxyl-transferase domain of the plastidic ACCase by standard PCR identified a point mutation resulting in an Ile-1781-Leu amino acid substitution only for the resistant biotype, R1. Further cloning of PCR product surrounding the 1781 region yielded two distinct ACCase gene sequences, Ile-1781 and Leu-1781. The amino acid substitution, Ile-1781-Leu in both resistant biotypes (R1 and R2), however, was revealed by next-generation sequencing of RNA using Illumina platform. A point mutation in the Ile-1781 codon leading to herbicide insensitivity in the ACCase enzyme has been previously reported in other grass species. Our research confirms that the Ile-1781-Leu substitution is present in pinoxaden-resistant D. ciliaris.

POST weed control atop the bed during strawberry production is limited to hand weeding, clopyralid, and acetyl CoA carboxylase inhibitors. Identification of additional modes of action is desirable to increase available options for producers and alleviate herbicide resistance concerns. The study objective was to screen sulfonylurea herbicides for safety of strawberry coordinated with efficacy against Carolina geranium. Herbicide treatments included metsulfuron-methyl, flazasulfuron, foramsulfuron, thifensulfuron-methyl, trifloxysulfuron-sodium, and rimsulfuron. Strawberry plants were heavily damaged by all herbicides apart from foramsulfuron. Although the strawberry plant was dramatically affected by the evaluated herbicides, demonstrating strong epinasty, there were no differences in resultant biomass at 31 d after treatment (DAT) compared to controls. Carolina geranium was severely injured by metsulfuron-methyl, flazasulfuron, and thifensulfuron-methyl, and moderately injured by foramsulfuron. There were consistent reductions in biomass by 31 DAT by metsulfuron-methyl and flazasulfuron. Overall, metsulfuron-methyl and flazasulfuron are suitable candidates for Carolina geranium control in row-middles. Foramsulfuron is a suitable candidate for additional field-based screening for utility in POST use in strawberry production atop the bed. Consideration toward doses, surfactants, timings, and cultivar tolerance may be necessary to minimize injury as observed in the greenhouse (15% to 20%).

Resistance to protoporphyrinogen oxidase (PPO) inhibitors was first observed in waterhemp in 2001 and was conferred by the deletion of a glycine residue at the 210th position (ΔGly-210) of the PPO enzyme. PPO-inhibitor resistance in Palmer amaranth was first observed in 2011, 10 years later. The objectives of this study were to directly compare PPO inhibitor responses in plants of both species with or without the ΔGly-210 mutation. Using greenhouse experiments, early (EPOST) and late (LPOST) postemergence dose responses using lactofen and fomesafen, and preemergence (PRE) dose responses using fomesafen and flumioxazin, were obtained for a sensitive and resistant population each of waterhemp and Palmer amaranth. An additional spray study confirmed each sensitive population used in the dose responses was representative of its respective species, with regards to PPO-inhibitor sensitivity. When treated at either POST timing, Palmer amaranth was more tolerant than waterhemp, and the ΔGly-210 mutation provided greater resistance in Palmer amaranth (48-fold to >3,440-fold, depending on timing and herbicide) than in waterhemp (31-fold to 123-fold). The level of tolerance in Palmer amaranth was striking; the sensitive Palmer amaranth population treated LPOST survived as well or better than the resistant waterhemp population treated EPOST. With PRE applications, response differences both between species and between resistant and sensitive populations generally were less pronounced, relative to POST applications. Collectively, this research indicates Palmer amaranth tolerance to POST-applied PPO inhibitors could have initially slowed (relative to waterhemp) evolution of resistance to these herbicides, and resistant and sensitive populations of both species are more likely to be effectively controlled with PRE rather than POST applications.

Skunk-vine (Paederia foetida L.) is an invasive vine native to eastern and southern Asia and is widely distributed in Florida, Hawaii, and other southeastern U.S. states; however, little research has focused on herbicide control. Greenhouse and field experiments were conducted to determine efficacy of aminocyclopyrachlor, aminopyralid, fluroxypyr, glyphosate, imazapic, triclopyr amine, and triclopyr ester at low and high labeled rates when foliar applied to P. foetida at various growth stages in greenhouse experiments. Longer-term control was evaluated in field experiments in central Florida using the same herbicides. PRE herbicides labeled for use in landscape plantings, including dimethenamid-P, flumioxazin, indaziflam, isoxaben, and prodiamine, were also evaluated in greenhouse trials by seeding containers with P. foetida seed. In greenhouse experiments, POST herbicides, including aminocyclopyrachlor, aminopyralid, glyphosate, both triclopyr formulations, and the high rate of fluroxypyr (0.24 kg ae ha−1), provided >90% control across all growth stages at 4 mo after treatment with no regrowth observed. Imazapic provided 49% to 89% control, with efficacy decreasing with P. foetida size, and generally provided less control than other treatments. Field experiments confirmed results from greenhouse studies. In PRE trials, flumioxazin and prodiamine provided better control than all other PRE herbicides evaluated, reducing shoot weights by 99% and 84%, respectively, compared with nontreated controls. Our data suggest all herbicides evaluated POST could potentially be used to manage P. foetida, although less control was achieved with imazapic compared with other herbicides. Further research is needed to determine herbicide efficacy on more mature plants and to develop application methods that would be less injurious to non-target vegetation. In landscapes, flumioxazin or prodiamine could be used for PRE control, but POST options that are labeled for landscape use should be identified in future research.

Italian ryegrass [Lolium perenne L. spp. multiflorum (Lam.) Husnot] is a troublesome weedy species in many regions of California. Its control has been chiefly dependent on herbicides due to their effectiveness and practicality and, as result, herbicide-resistant populations have been selected. Poor control of a population of L. multiflorum with paraquat was recently reported in a prune orchard in Hamilton City, CA. A series of experiments were carried out to characterize the response of this population to several POST herbicides, study the mechanisms of resistance, and investigate alternative chemical management options in tree crops. A known susceptible (S) and the suspected resistant population (PRHC) were subjected to greenhouse dose–response experiments with clethodim, fluazifop-P-butyl, glufosinate, glyphosate, paraquat, pyroxsulam, rimsulfuron, and sethoxydim. A 310-bp fragment of the EPSPS gene containing position 106 was sequenced from PRHC and S. Field experiments were carried out in a prune orchard with PRE herbicides commonly used by perennial crop growers in California. Greenhouse dose–response experiments confirmed that PRHC is resistant to paraquat, as well as multiply resistant to clethodim and glyphosate. The EPSPS gene of PRHC is heterozygous for glyphosate resistance at position 106, where one allele exhibited proline substituted by serine and the other by alanine. Field experiments with PRE herbicides indicated that tank mixes containing indaziflam and flumioxazin can provide adequate L. multiflorum control up to 150 d after treatment. Poor weed management practices, such as overreliance on a single site of action, have frequently been associated with the selection of herbicide-resistant L. multiflorum populations around the world, and adequate herbicide-resistance management programs are necessary for growers to maintain economic sustainability even after evolution of herbicide-resistant weeds in their fields.

Broadleaf species escape current integrated weed management strategies in strawberry [Fragaria×ananassa (Weston) Duchesne ex Rozier (pro sp.) [chiloensis×virginiana]] production. Clopyralid is a registered POST control option, but current application timings provide suppression of only some species. Earlier clopyralid application timings may increase spray coverage to weeds at the planting hole, but strawberry plant tolerance to applications shortly after transplant is unknown. The objectives of the study were to determine the degree of clopyralid tolerance when applied to mature strawberry plants according to current management strategies, whether clopyralid absorption and translocation were involved in the tolerance response demonstrated by mature strawberry plants, and whether clopyralid could be safely applied to immature strawberry plants shortly after transplant. Clopyralid caused no damage when applied to mature strawberry plants and did not affect crop height, number of crowns, flowers, immature berries, or yield. Maximal strawberry absorption of radiolabeled clopyralid was 82% of the recovered radioactivity and reached peak (90%) absorption at 15 h. Maximal total translocation of radioactivity from the treated leaf was 17% and reached peak translocation at 52 h. Translocation was primarily to the new leaves and reproductive structures. In the early-application experiment, damage induced by clopyralid for all application timings reached 0 by 8 wk after treatment. Across all timings, maximal damage at 140 g ha−1 was 17% when applied 14 d after transplant (DATr) and 56% at 28 g ha−1 when applied at 21 DATr. Clopyralid dose did not affect the number of crowns, aboveground biomass, or yield. There was some stunting in plant height (3%) by the high labeled dose of clopyralid. Labeled dose clopyralid applications appear safe for application timings closer to strawberry transplant, though considerations of leaf cupping should be taken under consideration for label changes.

Strawberry is an important horticultural crop in Florida. The long growing season and escapes from fumigation and PRE herbicides necessitate POST weed management to maximize harvest potential and efficiency. Alternatives to hand-weeding are desirable, but clopyralid is the only broadleaf herbicide registered for use. Weed control may be improved by early-season clopyralid applications, but at risk of high temperature and increased strawberry injury. The effect of temperature on clopyralid safety on strawberry is unknown. We undertook a growth chamber experiment using a completely randomized design to determine crop safety under various temperature conditions across acclimation, herbicide application, and post-application periods. There was no effect of clopyralid on the number of strawberry leaves across all temperatures. Damage to the strawberry manifested as leaf malformations. Acclimation temperatures affected clopyralid-associated injury (p=0.0309), with increased leaf malformations at higher temperatures (27 C) compared to lower (18 C) temperatures. Pre-treatment temperatures did not affect clopyralid injury. Post-application temperature also affected clopyralid injury (p=0.0161), with increased leaf malformations at higher temperatures compared to lower ones. Clopyralid application did not reduce flowering or biomass production in the growth chamber. If leaf malformations are to be avoided, consideration to growing conditions prior to application is advisable, especially if applying clopyralid early in the season.

Little information is published related to seed germination and seedling emergence of Japanese foxtail, a troublesome annual grass weed widely distributed in winter wheat fields in China. Three Japanese foxtail populations were studied under laboratory and greenhouse conditions, to determine the effects of different environmental factors on seed germination or seedling emergence. Chemical control is absolutely necessary in integrated management, and efficacy of POST herbicides against different growth stages of Japanese foxtail was evaluated. Germination rate was 90% or more when temperature ranged from 5 to 25 C, with germination onset shortened as temperature increased. Light was not required for germination to occur. For pH values ranging from 5 to10 there was no effect on seed germination. Japanese foxtail seed germination was sensitive to osmotic stress and completely inhibited at an osmotic potential of -1.1 MPa. The ‘1513’ population of Japanese foxtail demonstrated tolerance to soil salinity, with 98% germination at 80 mM NaCl compared with 25 and 40% germination for populations ‘1532’ and ‘1544’, respectively. High amounts of crop residue (10 t ha−1) suppressed Japanese foxtail emergence 38 to 55%. Germination of seeds placed at 160 C for 5 min was completely inhibited for dry seeds, with a similar effect at 130 C for pre-soaked seeds. Seed burial in the soil from 0 to 4 cm had no effect on seedling emergence, but burial at 7 cm completely inhibited seedling emergence. POST herbicides mesosulfuron-methyl (13.5 g ai ha−1), clodinafop-propargyl (67.5 g ai ha−1), pyroxsulam (13.5 g ai ha−1), pinoxaden (67.5 g ai ha−1) and isoproturon (1125 g ai ha−1) reduced plant dry weight 80% or more when applied at three- to seven-leaf stage, but control declined with application at later growth stages. The information from this study helps to develop an integrated approach to Japanese foxtail management.

Sweet potato clones were evaluated for metribuzin tolerance in field and greenhouse studies. ‘Tinian’ was the most tolerant and ‘SC-1149-19’ and ‘J-2’ were the most susceptible clones. ‘Jewel’, a clone widely grown commercially, was sensitive to metribuzin in the field and greenhouse. ‘Sumor’ and ‘White Triumph’ exhibited intermediate metribuzin tolerance. All metribuzin application-by-rate treatments reduced plant stands, caused season-long crop injury, and reduced yields. Metribuzin applied 3 wk posttransplant at 1.1 kg ha−1 did not reduce total yield of Tinian. Total yield of all the clones except Tinian were reduced by metribuzin regardless of timing or rate.

DPX PE350, an experimental herbicide, has shown excellent potential for controlling a wide range of problem broadleaf weeds in cotton. PPI, PRE, and POST applications of DPX PE350 at 0.1 and 0.2 kg ai/ha were evaluated under weedfree conditions in 1991 and 1992 for effects on ‘Paymaster HS26’ cotton growth, yield, and fiber quality. In 1991, DPX PE350 applied PPI, PRE, or POST did not affect cotton population, height, yield, or fiber quality. In 1992, DPX PE350 applied PPI at 0.1 or 0.2 kg/ha or PRE at 0.2 kg/ha injured the cotton and reduced yield and micronaire value.