Postemergence (POST) herbicides that control troublesome weeds during hybrid bermudagrass establishment via sprigs are limited due to potential turfgrass phytotoxicity and herbicide-resistant weeds. Research experiments were conducted in Blacksburg, VA, and Hope, AR, in 2016 and 2023 to evaluate herbicide programs to control goosegrass and smooth crabgrass and the response of hybrid bermudagrass sprigs to POST herbicides applied 3 to 5 wk after establishment (WAE). Another study was conducted to assess the tolerance of ‘Latitude 36’, ‘Tahoma 31’, and ‘TifTuf’ hybrid bermudagrass sprigs to POST herbicides applied 4 to 5 WAE. Thiencarbazone + foramsulfuron + halosulfuron did not injure hybrid bermudagrass > 6% across four cultivars and a total of 10 site-yr but reduced goosegrass and smooth crabgrass cover equivalent to the best-performing treatments. Topramezone + metribuzin injured turfgrass > 25% at 14 d after treatment (DAT), but tank mixing with thiencarbazone + foramsulfuron + halosulfuron reduced injury by 5% to 22%. Quinclorac injured hybrid bermudagrass 17% to 58%, depending on site, which was more than most other treatments. Mesotrione-, quinclorac-, or topramezone-based programs injured hybrid bermudagrass and also reduced turfgrass cover, the dark green color index, and the normalized difference vegetation index, but turfgrass recovered by 28 DAT. Results suggest that turfgrass managers have a variety of herbicides that can control smooth crabgrass and goosegrass during hybrid bermudagrass sprig establishment, but the margin of selectivity is relatively low for mesotrione, quinclorac, and topramezone and may be dependent on herbicide rate or hybrid bermudagrass cultivar.

Winter annual weeds begin to germinate as zoysiagrass enters winter dormancy in autumn. These weeds can suppress zoysiagrass shoot development the following spring through competition for sunlight, moisture, and nutrients. Previous research involving winter annual weed control in dormant turfgrass has been conducted primarily on bermudagrass, but less is known about how various herbicides used for this purpose will influence zoysiagrass after dormancy transition. Two field studies were conducted over 7 site-years between 2016 and 2020 to evaluate 17 herbicide treatments that are typically marketed for broadleaf weed control in spring and 18 herbicide treatments that are typically marketed for annual bluegrass control during winter for their effects on a variety of weeds and semidormant ‘Meyer’ and dormant ‘Zeon’ zoysiagrass, respectively. Glufosinate, glyphosate + simazine, and indaziflam + simazine controlled Persian speedwell by more than 90% and control was significantly greater with auxin-type and other herbicide combinations. Dandelion and Persian speedwell were better controlled with a combination of simazine and glyphosate than when glyphosate was applied alone. Glufosinate controlled dandelion, hairy bittercress, and Persian speedwell more effectively than glyphosate. In Meyer zoysiagrass, glyphosate and glufosinate controlled annual bluegrass equivalently, whereas in Zeon zoysiagrass, glyphosate controlled annual bluegrass better than glufosinate did. Foramsulfuron or treatments that contained simazine resulted in >90% control of annual bluegrass. A flumioxazin admixture with diquat, glufosinate, or glyphosate improved annual bluegrass control. Herbicide treatments that contain diquat, glufosinate, glyphosate, and metsulfuron alone or in a tank-mix should not be applied to Meyer zoysiagrass with 5% visual green turf cover due to high injury potential. In both studies, glufosinate was more injurious to Meyer and Zeon zoysiagrass than glyphosate. Overall, several herbicides that control annual bluegrass or broadleaf weeds can be safely applied to Zeon zoysiagrass during dormancy or Meyer zoysiagrass during post-dormancy transition.

Hair fescue is a perennial grass weed in lowbush blueberry fields that forms dense sods and reduces yield. As a result of natural tolerance or resistance of this grass to other currently registered herbicides growers rely on preemergence (PRE) applications of pronamide and postemergence (POST) applications of the Group 2 herbicides foramsulfuron and nicosulfuron + rimsulfuron for hair fescue management. This causes repeated application of Group 2 herbicides, which is compounded by the recent registration of flazasulfuron for POST suppression of hair fescue in lowbush blueberry. Mixtures of Group 2 herbicides with the amino acid–inhibiting herbicides glyphosate (Group 9) and glufosinate (Group 10), however, can improve weed control and may delay herbicide resistance development. This research used a factorial arrangement of Group 2 herbicides (none, foramsulfuron [35 g ai ha−1], nicosulfuron + rimsulfuron [13 + 13 g ai ha−1], flazasulfuron [50 g ai ha−1]) and mixtures (none, with glyphosate [902 g ae ha−1], and with glufosinate [750 g ai ha−1]) to identify possible mixtures that improve weed control and delay resistance development. Herbicides were applied in spring nonbearing year, fall bearing year, and fall nonbearing year, with each application timing conducted as a separate experiment. Foramsulfuron and nicosulfuron + rimsulfuron were not effective as fall applications, and spring applications of these herbicides with glyphosate or glufosinate improved hair fescue suppression. Glyphosate and glufosinate were more effective as fall rather than spring applications. Flazasulfuron was effective across all application timings, although its mixture with glufosinate generally improved hair fescue suppression. Flazasulfuron + glufosinate is tentatively recommended as an effective mixture for management of spring nonbearing-year and fall bearing-year hair fescue in lowbush blueberry.

Five johnsongrass populations collected from corn grown in northern Greece were studied to elucidate the levels and mechanisms of resistance to acetolactate synthase (ALS)- and acetyl-CoA carboxylase (ACCase)-inhibiting herbicides. Whole-plant response assays indicated that two populations were highly cross-resistant to all ALS inhibitors tested (foramsulfuron, nicosulfuron, rimsulfuron, and imazamox) but were effectively controlled by the recommended rate of the ACCase-inhibiting herbicides propaquizafop and clethodim. The ALS gene sequence revealed a point mutation that resulted in the substitution of Trp574 by Leu in the ALS enzyme, suggesting that the resistance mechanism is target-site mediated. These findings highlight a serious threat against the sustainable use of the ALS-inhibiting herbicides in controlling johnsongrass and other grass weeds in cornfields, suggesting rotational use of herbicides with different modes of action, along with the use of nonchemical methods, for viable Johnsongrass management.

Hair fescue is a common perennial grass that reduces yields in lowbush blueberry fields. This grass is suppressed with nonbearing-year foramsulfuron applications, though suppression may be improved through use of sequential glufosinate and foramsulfuron applications. The objective of this research was to determine the main and interactive effects of fall bearing-year glufosinate applications, spring nonbearing-year glufosinate applications, and spring nonbearing-year foramsulfuron applications on hair fescue. The experiment was a 2 by 2 by 2 factorial arrangement of fall bearing-year glufosinate application (0, 750 g ai ha–1), spring nonbearing-year glufosinate application (0, 750 g ai ha–1), and spring nonbearing-year foramsulfuron application (0, 35 g ai ha–1) arranged in a randomized complete block design at lowbush blueberry fields located in Parrsboro and Portapique, NS, Canada. Fall bearing-year glufosinate applications, spring nonbearing-year glufosinate applications, and spring nonbearing-year foramsulfuron applications alone provided inconsistent hair fescue suppression. Fall bearing-year glufosinate applications followed by spring nonbearing-year foramsulfuron applications, however, reduced nonbearing-year total tuft density, flowering-tuft density, and flowering-tuft inflorescence number at each site and reduced seed production at Portapique. Sequential fall bearing-year and spring nonbearing-year glufosinate applications or sequential spring nonbearing-year glufosinate and foramsulfuron applications reduced flowering-tuft density and flowering-tuft inflorescence number at each site but did not consistently reduce total tuft density. Sequential herbicide treatments reduced bearing-year seedling density and may therefore contribute to hair fescue seed bank management in lowbush blueberry.

Hair fescue is a common tuft-forming perennial grass weed that reduces yields and hinders mechanical harvest in lowbush blueberry fields. PRE terbacil applications traditionally controlled hair fescue but currently only provide suppression in most fields. Terbacil use has not, however, been evaluated in conjunction with other currently registered herbicides in lowbush blueberry. The objective of this research was to evaluate a range of terbacil-based herbicide treatments for hair fescue management in lowbush blueberry. The experiment was conducted at three lowbush blueberry fields in Nova Scotia, Canada. Spring nonbearing-year terbacil applications (2,000 g ai ha–1) exhibited variable efficacy on hair fescue with reduced total tuft density at one site and reduced flowering-tuft density and flowering-tuft inflorescence number at two sites. Suppression was limited to the year of application only. Terbacil followed by (fb) foramsulfuron (35 g ai ha–1) did not improve suppression. A terbacil tank mixture with glufosinate (750 ai ha–1), however, reduced flowering-tuft density and flowering-tuft inflorescence number at each site and reduced total tuft density at one site, suggesting improved suppression with terbacil + glufosinate relative to terbacil alone. Terbacil + glufosinate fb foramsulfuron gave additional reductions in total tuft density at two sites and reduced bearing-year flowering-tuft density at two sites, indicating that hair fescue suppression with this herbicide combination extends into the bearing year. Although less effective than the industry standard pronamide applications, terbacil + glufosinate or terbacil + glufosinate fb foramsulfuron could be used as part of a weed management program for hair fescue in lowbush blueberry.

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%).

Hair fescue is a widespread, seed-limited perennial grass in lowbush blueberry fields. Growers rely on pronamide, an expensive and difficult herbicide to use, for hair fescue management. Recent herbicide registrations provide opportunity to reduce pronamide use, though effects of these herbicides on hair fescue suppression and seedbank reduction are not well understood. The objectives of this research were to determine (1) the effects of herbicides currently registered in lowbush blueberry on suppression of hair fescue tufts and (2) whether suppression of hair fescue with these herbicides reduces hair fescue seedbanks. Pronamide gave the most consistent reductions in flowering tuft density, though applications after both autumn pruning and autumn of the nonbearing year were required to reduce the hair fescue seedbank by >60% across sites. Nonbearing-year hexazinone applications did not control hair fescue or reduce the seedbank. Nonbearing-year terbacil applications reduced flowering tuft density, but hair fescue recovered in the bearing year, and the seedbank was not reduced. Glufosinate applications following autumn pruning or in the spring of the nonbearing year did not suppress hair fescue or reduce the seedbank. Spring nonbearing-year foramsulfuron applications, alone or after autumn or spring glufosinate applications, reduced hair fescue flowering tuft density, but hair fescue recovered in the bearing year, and the seedbank was not reduced. In contrast, autumn and spring glufosinate applications followed by spring nonbearing-year foramsulfuron applications, when combined with autumn nonbearing-year pronamide applications, reduced flowering tuft density in both the nonbearing and bearing years and reduced the hair fescue seedbank by 58% to 83% across sites. Results indicate that hair fescue seedbanks can be reduced in lowbush blueberry fields and that a reduction in pronamide use will require alternative bearing-year treatments to prevent tuft recovery and seed production.

Goldenrods are common perennial weeds in lowbush blueberry fields in Nova Scotia. Management options are limited to mowing and suppression with POST mesotrione applications. The objectives of this research were to (1) compare efficacy of single versus sequential nonbearing-year POST mesotrione applications on goldenrod (2) identify the optimal interval between sequential POST mesotrione applications (3) evaluate nonbearing-year POST bicyclopyrone applications on goldenrod, and (4) evaluate nonbearing-year summer and fall herbicide spot treatments on goldenrod. POST mesotrione applications at 144 g ai ha−1 caused 39% to 77% injury but did not reduce goldenrod shoot density. In contrast, mesotrione applications at 144 g ai ha−1 followed by sequential mesotrione application at 14, 21, or 28 days after initial treatment caused greater than 90% injury to goldenrod and reduced both nonbearing- and bearing-year shoot density. POST bicyclopyrone applications at 50 g ai ha−1 caused 69% to 80% injury to goldenrod but did not reduce shoot density. A bicyclopyrone plus mesotrione tank mixture did not improve goldenrod control relative to mesotrione or bicyclopyrone alone. Summer spot applications of glyphosate (7.24 g ae L water−1), glufosinate (0.75 g ai L water−1), and mesotrione (0.72 g ai L water−1) consistently injured goldenrod and reduced both nonbearing- and bearing-year shoot density. Summer spot applications of bicyclopyrone (0.25 g ai L water−1), flazasulfuron (0.31 g ai L water−1), dicamba (1 g ae L water−1), dicamba plus diflufenzopyr (0.7 g ae L water−1 plus 0.3 g ai L water−1), triclopyr (1.68 g ai L water−1), clopyralid (0.08 g ai L water−1), tribenuron methyl (0.2 g ai L water−1), and foramsulfuron (0.2 g ai L water−1) injured goldenrod but did not consistently reduce shoot density. When these herbicides were evaluated as fall spot applications, only glyphosate reduced goldenrod shoot density in the year after application.

Reductions in MSMA use for weed control in turfgrass systems may have led to increased common carpetgrass infestations. The objective of our research was to identify alternative POST herbicides for control of common carpetgrass using field and controlled-environment experiments. Field applications of MSMA (2.2 kg ai ha−1) and thiencarbazone + iodosulfuron + dicamba (TID) (0.171 kg ai ha−1) resulted in the greatest common carpetgrass control 8 wk after initial treatment (WAIT): 94% and 91%, respectively. Thiencarbazone + foramsulfuron + halosulfuron (TFH) (0.127 kg ai ha−1) applied in the field resulted in 77% control 8 WAIT, whereas all other treatments were ≤19% effective at 8 WAIT. All treatments resulted in greater common carpetgrass control when applied in the greenhouse. Applications of MSMA, TFH, and TID resulted in the highest common carpetgrass control in the greenhouse 8 WAIT: 94%, 94%, and 91%, respectively. Control with nicosulfuron (0.035 kg ai ha−1) and trifloxysulfuron (0.028 kg ai ha−1) (81% and 75%, respectively) was greater in the greenhouse than observed in the field 8 WAIT. Sequential applications of foramsulfuron (0.058 kg ai ha−1) resulted in only ≤11% common carpetgrass control 8 WAIT, regardless of application site. All herbicide treatments in the greenhouse resulted in reduced aboveground common carpetgrass biomass 8 WAIT compared to the nontreated control (12.9 g). Aboveground biomasses of common carpetgrass in response to MSMA, TID, TFH, nicosulfuron, and trifloxysulfuron were 1.6 to 2.1 g, regardless of treatment. Reduced efficacy of foramsulfuron was reflected in greater biomass (4.7 g) in response to treatments. Thiencarbazone + iodosulfuron + dicamba may be an alternative to MSMA for common carpetgrass control; however, long-term assessment may be warranted to evaluate treatment effectiveness. Further investigation into application timing may be necessary to enhance the efficacy of TFH for the control of common carpetgrass.

Common chickweed [Stellaria media (L.) Vill.] is an annual weed found in grain fields and pastures. This creeping weed produces a mat-like canopy that competes with crop seedlings for light and nutrients. This species is almost exclusively autogamous. Acetolactate synthase (ALS)-inhibiting herbicides are frequently used to control this broadleaf weed, and two mutations in the S. media ALS gene (Pro-197-Gln and Trp-574-Leu) have been reported to confer herbicide resistance. Seeds from several plants that survived an application of thifensulfuron-methyl/tribenuron-methyl (16 g ai ha−1) were collected from the same field in Québec, Canada. Seedlings were grown, tested for the presence of mutations in the ALS gene, and treated with different rates of foramsulfuron, flumetsulam, and imazethapyr, each belonging to different families of ALS inhibitors. Two herbicide resistance–conferring mutations were identified in this population. One biotype had the previously reported Pro-197-Gln, while a new mutation, Pro-197-Ser, was identified in different plants from the same population. The new mutation (Pro-197-Ser) confers a lower level of resistance to sulfonylureas than Pro-197-Gln, and both biotypes are susceptible to imizadolinone and triazolopyrimidines.

Tropical signalgrass (TSG) is one of the most problematic weeds found on golf courses, sports fields, and sod farms in south Florida. The recent ban of monosodium methane-arsonate (MSMA), an organic arsenical herbicide, from urban areas in Florida has left turfgrass managers searching for effective management options. In an effort to avoid relying solely on POST chemical control, this research examined the effect of combining a cultural practice, verticutting, along with PRE and POST herbicides as an integrated weed management approach to controlling TSG in hybrid bermudagrass. Field experiments were conducted at multiple locations over 2 yr in south Florida to: (1) determine whether verticutting before herbicide applications increases TSG control and (2) identify herbicide programs that effectively control TSG. No interactions between verticutting and herbicide programs were detected, but verticutting consistently provided a slight reduction (8% averaged across herbicide treatments) in TSG cover. Treatments containing a PRE herbicide resulted in a significant reduction (20% to 50%) in TSG cover at 52 wk after initial treatment (WAIT), while some POST herbicide treatments reduced TSG cover to <20% at 52 WAIT. A study was conducted to determine which POST herbicide combinations were most efficacious in controlling TSG. Amicarbazone alone provided ≤35% TSG control at 8 and 12 WAIT, but synergistic responses were observed between amicarbazone and mesotrione, trifloxysulfuron, and thiencarbazone+foramsulfuron+halosulfuron. Two- and three-way combinations of amicarbazone with these POST herbicides resulted in >80% TSG control at 4, 8, and 12 WAIT, with some reaching 100% TSG control at 4 WAIT. Based on these data, verticutting may provide limited complementary control, but certain combinations of POST herbicides exhibited excellent (>95%) TSG control.

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

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.

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.

The duration of the soil activity of an acetolactate synthase-(ALS) inhibiting herbicide which is currently under approval for sugar beet cultivation was determined in a field trial series in Germany in 2013 and 2014. The herbicide containing foramsulfuron (FSN; 50 g L−1) and thiencarbazone-methyl (TCM; 30 g L−1) was applied in different dosages (25+15, 37.5+22.5 and 50+30 g FSN+TCM ha−1) to the bare soil. Five weed species (rapeseed, common lambsquarters, wild chamomile, blackgrass, barnyardgrass) were sown at 5, 10, 15 and 20d after application. The duration of the soil activity was assessed by determining percent weed control in the treated plots. The longest duration was observed after applying 50+30 g FSN+TCM ha−1, but the influence of environment was much stronger than the dosage effect. The mean duration of soil activity was 10 to 15 d in 2013 and longer than 20 d in 2014. Differences among weed species in their response to the herbicide treatments were small.

Foramsulfuron (AE F130360) is a sulfonylurea herbicide for postemergence control of grasses and some broadleaf weeds in corn. Greenhouse and laboratory experiments were conducted to determine the physiological basis for differential tolerance of corn hybrids to foramsulfuron. Differences in corn tolerance were quantified by determining the herbicide rate required to cause injury and reduce corn height by 15% (GR15). Seven hybrids were screened in the greenhouse where GR15 values indicated that the some of the corn hybrids were sensitive to foramsulfuron. All but one of these hybrids exhibited an increase in tolerance when the safener, isoxadifen-ethyl, was applied with foramsulfuron. Experiments using 14C-foramsulfuron were conducted to determine whether isoxadifen-ethyl affected foramsulfuron absorption, translocation, and metabolism in two of the corn hybrids. There was no difference in absorption between a sensitive hybrid Novartis 58D1 and a more tolerant hybrid Novartis 59Q9, but the addition of isoxadifen-ethyl increased foramsulfuron absorption in both hybrids 24 h after treatment. Less than 1 and 3% of the 14C-foramsulfuron was translocated to plant portions above and below the treated leaf, respectively. Differences in hybrid tolerance were primarily due to differential herbicide metabolism. Foramsulfuron metabolism, with and without isoxadifen-ethyl, was similar at 4 h after treatment for both the sensitive and tolerant hybrids. However, by 24 h after treatment the more tolerant hybrid metabolized foramsulfuron to more polar compounds to a greater degree than the sensitive hybrid.

Sulfonylurea herbicides used in turfgrass—including chlorsulfuron, flazasulfuron, foramsulfuron, halosulfuron, metsulfuron, rimsulfuron, sulfometuron, sulfosulfuron, and trifloxysulfuron—are all weak acids, with disassociation constants ranging from 3.3 to 5.2. Sulfonylureas are used at low rates ranging from 4 to 280 g ha−1. Although these use rates put their soil concentration in parts per billion, they still have residual activity with variable persistence. They have limited susceptibility to soil leaching with weak adsorption to soil clay minerals. Sulfonylurea herbicides used in turfgrass have variable soil organic matter adsorption, which is soil dependent. The persistence and activity of these sulfonylureas are affected by soil pH. At soil pH of 7.0 and greater, some of these sulfonylurea herbicides tend to persist for longer periods with half-lives extending into years rather than days. In normal use patterns with soil pH of 7.0 and less, dissipation occurs via chemical hydrolysis and microbial degradation with half-lives ranging from days to months. Overall, sulfonylurea herbicide adsorption is negatively correlated to increasing pH (increased persistence) and positively correlated to increased organic matter (decreased activity).

Field trials were conducted in 2004 and 2005 to identify sulfonylurea (SU) herbicides that would provide improved weed control, minimal soil residual, and crop safety to SU-resistant chicory. SU-resistant chicory had previously been selected in vitro for resistance to chlorsulfuron. Our research evaluated three commercial, nonresistant and three breeding lines of SU-resistant chicory. Each of the cultivars was treated POST at the two true-leaf growth stage with either foramsulfuron, rimsulfuron, rimsulfuron plus thifensulfuron, tribenuron, thifensulfuron, thifensulfuron plus tribenuron, triflusulfuron, flumetsulam, or imazamox at normal use rates. Established plant densities and root yields of SU-resistant chicory breeding lines were greater than or equal to the densities and root yields of commercial cultivars. The plant density of commercial chicory cultivars was reduced by rimsulfuron, rimsulfuron plus thifensulfuron, tribenuron, and thifensulfuron plus tribenuron, but SU-herbicides did not reduce the density of SU-resistant breeding lines. SU-resistant chicory differed in cross-resistance to SU-herbicides, with tribenuron causing the most crop injury and thifensulfuron, the least. Weed control varied between the SU-herbicides. The greatest reduction in weed biomass occurred with tribenuron, thifensulfuron plus tribenuron, and rimsulfuron plus thifensulfuron; the least reduction occurred with triflusulfuron, foramsulfuron, and rimsulfuron. Chicory root yields comparable to the hand-weeded treatment were achieved with rimsulfuron plus thifensulfuron and thifensulfuron plus tribenuron treatments. The SU herbicides that met the initial project objectives of crop tolerance and improved weed control were combinations of rimsulfuron plus thifensulfuron and thifensulfuron plus tribenuron.

Tropical signalgrass (TSG) has become a serious weed problem in tropical and subtropical regions such as Florida in recent years in association with the ban of organic arsenical herbicide use in turf. The purpose of this research was to identify alternative POST herbicides that control TSG. Two field experiments were conducted in bermudagrass golf course fairways in south and central Florida in 2014 and 2015. Several nonorganic arsenical herbicide treatments controlled TSG. In the first experiment, treatments containing amicarbazone alone and in combination with other herbicides provided > 97% TSG control 12 wk after initial treatment (WAIT) in 2014 and 2015. These included a single application of amicarbazone at 0.49 kg ai ha−1, or sequential applications of amicarbazone at 0.25 kg ha−1 in combination with foramsulfuron at 0.04 kg ai ha−1, sulfentrazone + imazethapyr at 0.25 kg ai ha−1, thiencarbazone + foramsulfuron + halosulfuron at 0.14 kg ai ha−1, and thiencarbazone + iodosulfuron + dicamba at 0.18 kg ai/ae ha−1. In the second experiment, sequential applications of thiencarbazone + foramsulfuron + halosulfuron at 0.14 kg ha−1 in combination with either quinclorac at 0.84 kg ai ha−1 or metribuzin at 0.28 kg ai ha−1 provided ≥ 85% TSG control 12 WAIT in both years.