Yellow and knotroot foxtail are two common weed species infesting turfgrass and pastures in the southeastern region of the United States. Yellow and knotroot foxtail share morphological similarities and are frequently misidentified by weed managers, thus leading to confusion in the herbicide selection. Greenhouse research was conducted to evaluate the response of yellow and knotroot foxtail to several turfgrass herbicides: pinoxaden (35 and 70 g ai ha-1), sethoxydim (316 and 520 g ai ha-1), thiencarbazone+dicamba+iodosulfuron (230 g ai ha-1), nicosulfuron+rimsulfuron (562.8 g ai ha-1), metribuzin (395 g ha-1), sulfentrazone (330 g ai ha-1), sulfentrazone+imazethapyr (504 g ai hai-1), imazaquin (550 g ai ha-1). All treatments controlled yellow foxtail >87% with more than 90% reduction of the biomass. By comparison, only sulfentrazone alone controlled knotroot foxtail 90% and completely reduced above-ground biomass. Sethoxydim (520 g ai ha-1), metribuzin, and imazaquin controlled knotroot foxtail >70% at 28 DAA. In a rate response evaluation, non-linear regression showed yellow foxtail was approximately eight times more susceptible to pinoxaden and two times more susceptible to sethoxydim than knotroot foxtail based on log (WR50) values, which were 50% reduction in fresh weight. Our research indicates that knotroot foxtail is more difficult to control across a range of herbicides making differentiation of these two species important before herbicides are applied.

Goosegrass and smooth crabgrass in creeping bentgrass turf are difficult to control due to a lack of selective herbicides. Based on preliminary field observations, we hypothesized that paclobutrazol and flurprimidol would reduce the overall competitiveness of goosegrass and smooth crabgrass in creeping bentgrass. Greenhouse and field studies were designed to evaluate the effect of several plant growth regulators (PGRs) on goosegrass and smooth crabgrass competitive indices. In greenhouse studies, flurprimidol, paclobutrazol, trinexapac-ethyl, and prohexadione-calcium were applied either preemergence only or preemergence plus two biweekly postemergence applications to goosegrass and smooth crabgrass plants to simulate the first 1.5 mo of typical PGR programs used on golf courses. Two weeks after the final postemergence treatment, aboveground biomass and root biomass were recorded. Programmatic flurprimidol and paclobutrazol applications reduced smooth crabgrass aboveground biomass by 67% and 69%, respectively, and more than trinexapac ethyl or prohexadione-calcium. When averaged across application programs, flurprimidol and paclobutrazol reduced smooth crabgrass root biomass by 74% and goosegrass biomass by 73% to 80%. Field studies were established to further evaluate the influence of PGRs on smooth crabgrass coverage in creeping bentgrass turf. Treatments consisting of flurprimidol, trinexapac-ethyl, flurprimidol plus trinexapac-ethyl, paclobutrazol, and fenoxaprop-p were applied every 3 wk from April to August. Weed coverage data were collected throughout the growing season, and final smooth crabgrass control data were collected at the end of the season. In general, flurprimidol-containing treatments more effectively reduced smooth crabgrass coverage throughout the growing season than trinexapac ethyl. After the studies, regimens that contained flurprimidol controlled smooth crabgrass by 68% to 73%, greater than any other PGR program evaluated. Results from these studies indicate that flurprimidol may be used to effectively control smooth crabgrass or goosegrass in creeping bentgrass turf. These are the first reported data regarding the use of flurprimidol for smooth crabgrass or goosegrass control in turf.

Methiozolin is labeled for goosegrass and smooth crabgrass control in golf course putting greens, but no peer-reviewed literature exists regarding this use. Greenhouse experiments were conducted evaluating goosegrass and smooth crabgrass response to increasing rates of methiozolin as affected by weed growth stage. In general, as weed growth stage increased, the methiozolin rate required to reduce weed biomass 90% (WR90) increased. Goosegrass was more sensitive to preemergence-applied methiozolin than smooth crabgrass, and the WR90 was 30.4 and 118 g ai ha–1 for goosegrass and smooth crabgrass, respectively. However, smooth crabgrass was generally more sensitive to postemergence-applied methiozolin than goosegrass. Subsequent field studies were conducted to evaluate goosegrass and smooth crabgrass control with methiozolin applied singularly or sequentially at standard preemergence timings. Results indicated methiozolin applied singularly or sequentially at the label-recommended rate (500 g ha–1) is not persistent enough to provide season-long control of goosegrass and smooth crabgrass. Ten field studies were conducted in Alabama, California, Florida, and Virginia to evaluate frequent methiozolin application programs with the objective of providing selective, season-long goosegrass and smooth crabgrass control. Results from these studies indicate methiozolin can be safely applied to hybrid bermudagrass and creeping bentgrass putting greens despite exceeding the yearly maximum use rate for putting greens (2,500 g ha–1) with some treatments. Methiozolin effectively controlled smooth crabgrass throughout the growing season in California and Virginia when 10 biweekly applications were applied at 250 g ha–1 or higher. In Florida, methiozolin did not acceptably (80%) control goosegrass regardless of application rate. In Virginia, methiozolin acceptably controlled goosegrass only when applied at rates and frequencies that exceeded the maximum yearly methiozolin usage rate. These data indicate that methiozolin has the potential to control smooth crabgrass preemergence when applied frequently, but does not provide acceptable goosegrass control at labeled rates.

Herbicide resistance coupled with a dearth of selective herbicide options has increased the complexity of annual bluegrass control in hybrid bermudagrass putting greens. Cumyluron, endothall, and methiozolin are herbicides that control annual bluegrass by inhibiting novel sites of action compared with the herbicides currently used for turfgrass management in the United States. However, peer-reviewed literature contains no information on hybrid bermudagrass putting green tolerance to these herbicides. Sixteen field studies were established on eight golf greens in Midlothian, VA, in 2021 and 2022 to evaluate effects of cumyluron, endothall, methiozolin, pronamide, and trifloxysulfuron on bermudagrass spring transition. The 16 studies were split equally between initiation during full dormancy versus mid-spring transition. Methiozolin applied at 500 and 1,000 g ai ha−1 typically increased the heat units (growing degree days with a base temperature of 15 C) required for hybrid bermudagrass to visibly achieve 90% green coverage (T90) when applied to fully dormant hybrid bermudagrass. This delay in green coverage was more pronounced at sites where hybrid bermudagrass vigor was seemingly reduced via abiotic stressors. Endothall was generally more injurious than all other treatments when applied to hybrid bermudagrass during mid-transition. Endothall applied at 840 g ai ha−1 injured hybrid bermudagrass for 0 to 9 d over a threshold of 30% (DOT30), depending on location. In two site-years characterized by increased abiotic stress, methiozolin applied at 1,000 g ai ha−1 caused 44 DOT30. Cumyluron never injured hybrid bermudagrass by more than 30% or delayed T90 regardless of application timing. These results indicate that methiozolin should be applied only within labeled rates to actively growing hybrid bermudagrass putting greens, cumyluron can be safely applied at 6,450 g ai ha−1 to dormant or actively growing bermudagrass greens, and endothall applications should be limited to dormant bermudagrass greens unless transient phytotoxicity is acceptable.

Few herbicides are registered for goosegrass control in creeping bentgrass turfgrass. Topramezone controls goosegrass and is labeled for use on creeping bentgrass, but potential injury risks lead many turf managers to frequently apply it at a low-dose. This application practice increases the likelihood that topramezone treatments will be mixed with fungicide treatments. Previous research found that fungicides can reduce the activity of some herbicides, but their effects on topramezone efficacy are unknown. Four studies were established between Blacksburg, VA, and North Brunswick, NJ, in 2021 to determine whether chlorothalonil reduces goosegrass control from topramezone. In controlled environment dose-response studies the amount of topramezone needed to reduce goosegrass biomass by 50% increased from 3.04 g ha−1 to 5.27 g ha−1 when chlorothalonil (7,400 g ha−1) was added to the mixture. In field experiments, topramezone at 3.7 and 6.1 g ha−1 controlled goosegrass by 50% and 63%, respectively, at 42 d after treatment when averaged across herbicide admixtures. The addition of chlorothalonil alone and chlorothalonil plus acibenzolar-S-methyl to topramezone reduced goosegrass control from 73% to 52% and 45%, respectively, when averaged across topramezone rate. From these studies we can conclude that chlorothalonil has the potential to reduce goosegrass control when topramezone is applied at the maximum allowable rate (6 g ae ha−1) or less. This is the first report of fungicides acting to reduce herbicidal weed control efficacy in turfgrass systems.

Data from a national survey of 348 U.S. sports field managers were used to examine the effects of participation in Cooperative Extension events on the adoption of turfgrass weed management practices. Of the respondents, 94% had attended at least one event in the previous 3 yr. Of this 94%, 97% reported adopting at least one practice as a result of knowledge gained at an Extension turfgrass event. Half of the respondents had adopted four or more practices; a third adopted five or more practices. Nonchemical, cultural practices were the most-adopted practices (65% of respondents). Multiple regression analysis was used to examine factors explaining practice adoption and Extension event attendance. Compared to attending one event, attending three events increased total adoption by an average of one practice. Attending four or more events increased total adoption by two practices. Attending four or more events (compared to one event) increased the odds of adopting six individual practices by 3- to 6-fold, depending on the practice. This suggests that practice adoption could be enhanced by encouraging repeat attendance among past Extension event attendees. Manager experience was a statistically significant predictor of the number of Extension events attended but a poor direct predictor of practice adoption. Experience does not appear to increase adoption directly, but indirectly, via its impact on Extension event attendance. In addition to questions about weed management generally, the survey asked questions specifically about annual bluegrass management. Respondents were asked to rank seven sources of information for their helpfulness in managing annual bluegrass. There was no single dominant information source, but Extension was ranked more than any other source as the most helpful (by 22% of the respondents) and was ranked among the top three by 53%, closely behind field representative/local distributor sources at 54%.

Annual bluegrass is a troublesome weed in turfgrass, with reported resistance to at least 12 herbicide sites of action. The mitotic-inhibiting herbicide pronamide has both preemergence and postemergence activity on susceptible annual bluegrass populations. Previous studies suggest that postemergence activity may be compromised due to lack of root uptake, as well as target-site- and translocation-based mechanisms. Research was conducted to determine the effects of spray droplet spectra on spray coverage and control of annual bluegrass with pronamide, flazasulfuron, and a mixture of pronamide plus flazasulfuron. Herbicides were delivered to annual bluegrass plants having two to three leaves via five different spray spectra based on volume median diameters (VMD) of 200, 400, 600, 800, and 1,000 µm. Fluorescent tracer dye was added to each treatment solution to quantify the effects of herbicide and spray droplet spectra on herbicide deposition. In another experiment, the efficacy of 0.58, 1.16, and 2.32 kg pronamide ha−1; 0.022, 0.044, and 0.088 kg flazasulfuron ha−1, or a combination of the two, were assessed in iteration with droplet spectrum sprays of 400 and 1,000 µm on two pronamide-resistant and two pronamide-susceptible annual bluegrass populations. Spray droplet spectrum affected the deposition of pronamide and flazasulfuron, applied alone and in combination. Pronamide foliar deposition decreased with increasing droplet spectra. Pronamide efficacy was affected by droplet spectrum, with the largest (1,000 µm) exhibiting improved control. Flazasulfuron efficacy and pronamide plus flazasulfuron efficacy were not affected by droplet spectra. Pronamide plus flazasulfuron mixture controlled all four populations more effectively than pronamide alone, regardless of droplet spectra. A mixture of pronamide plus flazasulfuron applied with relatively large droplets may be optimal for annual bluegrass control, which offers valuable insights for optimizing herbicide application and combatting herbicide resistance. However, applications in this controlled-growth pot study may not mimic conditions in which thatch and turfgrass canopy limit the soil deposition of pronamide.

The mitotic-inhibiting herbicide pronamide controls susceptible annual bluegrass (Poa annua L.) pre- and postemergence, but in some resistant populations, postemergence activity is compromised, hypothetically due to a target-site mutation, lack of root uptake, or an unknown resistance mechanism. Three suspected pronamide-resistant (LH-R, SC-R, and SL-R) and two pronamide-susceptible (BS-S and HH-S) populations were collected from Mississippi golf courses. Dose–response experiments were conducted to confirm and quantify pronamide resistance, as well as resistance to flazasulfuron and simazine. Target sites known to confer resistance to mitotic-inhibiting herbicides were sequenced, as were target sites for herbicides inhibiting acetolactate synthase (ALS) and photosystem II (PSII). Pronamide absorption and translocation were investigated following foliar and soil applications. Dose–response experiments confirmed pronamide resistance of LH-R, SC-R, and SL-R populations, as well as instances of multiple resistance to ALS- and PSII-inhibiting herbicides. Sequencing of the α-tubulin gene confirmed the presence of a mutation that substituted isoleucine for threonine at position 239 (Thr-239-Ile) in LH-R, SC-R, SL-R, and BS-S populations. Foliar application experiments failed to identify differences in pronamide absorption and translocation between the five populations, regardless of harvest time. All populations had limited basipetal translocation—only 3% to 13% of the absorbed pronamide—across harvest times. Soil application experiments revealed that pronamide translocation was similar between SC-R, SL-R, and both susceptible populations across harvest times. The LH-R population translocated less soil-applied pronamide than susceptible populations at 24, 72, and 168 h after treatment, suggesting that reduced acropetal translocation may contribute to pronamide resistance. This study reports three new pronamide-resistant populations, two of which are resistant to two modes of action (MOAs), and one of which is resistant to three MOAs. Results suggest that both target site– and translocation-based mechanisms may be associated with pronamide resistance. Further research is needed to confirm the link between pronamide resistance and the Thr-239-Ile mutation of the α-tubulin gene.

False-green kyllinga is a problematic C4 perennial Cyperaceae species. Previous research examined herbicide efficacy but has not integrated nonchemical practices with herbicides. Replicate field experiments were conducted to evaluate late-summer postemergence applications of herbicides in combination with turf-type tall fescue interseeding for false-green kyllinga control. Seven herbicide treatments and a nontreated control formed a complete factorial, with tall fescue interseeding or no seeding (eight-by-two factorial). Six herbicide treatments consisted of single postemergence applications of halosulfuron-methyl (70 g ha–1), imazosulfuron (420 g ha–1), and sulfentrazone + carfentrazone (280 + 30 g ha–1) applied 4 wk before tall fescue interseeding (WBS) and the day of interseeding. Glyphosate (220 g ae ha–1) applied the day of interseeding was the seventh herbicide treatment. Tall fescue was interseeded in September, and false-green kyllinga control was evaluated the following summer. In combination with tall fescue interseeding, imazosulfuron and halosulfuron applied 4 WBS as well as glyphosate applied the day of interseeding controlled false-green kyllinga better than all other treatments. In July, imazosulfuron and halosulfuron treatments applied 4 WBS and combined with interseeding had 1% to 6% false-green kyllinga cover, respectively, compared to 28% and 62% cover, respectively, without interseeding. Interseeding alone controlled false-green kyllinga <50%. Imazosulfuron, halosulfuron, and sulfentrazone + carfentrazone applied the day of seeding severely injured emerging tall fescue seedlings and reduced turfgrass quality the following spring. Applying imazosulfuron or halosulfuron in late summer and interseeding turf-type tall fescue 4 wk later or applying glyphosate the day of seeding are effective strategies for postemergence false-green kyllinga control. Integrating herbicides and the cultural practice of tall fescue interseeding provided more false-green kyllinga control than either practice alone.

Acetolactate synthase (ALS) inhibitors provide postemergence control of green kyllinga (Kyllinga brevifolia Rottb.) in turfgrass and other cropping systems. A suspected resistant (R) biotype of K. brevifolia was collected from a golf course and evaluated for resistance to ALS inhibitors. In greenhouse experiments, the sulfosulfuron rates required to cause 50% shoot biomass reduction from the nontreated at 4 wk after treatment (WAT) were 10 and 792 g ai ha−1 for the susceptible (S) and R biotypes, respectively. The rates required to cause 50% injury at 4 WAT were 189 and >3,360 g ai ha−1, respectively. In other experiments, shoot mass of the R biotype was not reduced by imazaquin, trifloxysulfuron-sodium, pyrimisulfan, thiencarbazone + foramsulfuron + halosulfuron, florasulam + halauxifen-methyl, and bentazon compared with the nontreated, while sulfentrazone reduced biomass similarly for both R and S biotypes. Gene sequencing of the R biotype revealed a mutation at Asp-376-Glu that has previously conferred resistance to five families of ALS inhibitors. This is the first report of ALS-inhibitor resistance in K. brevifolia.

The annual bluegrass weevil (ABW) is a pest of fine turfgrass, but recent research has found that withholding insecticides for ABW control can reduce annual bluegrass cover. The objective of this research was to evaluate threshold-based insecticide and paclobutrazol programs for annual bluegrass control. The effect of three insecticide programs (preventive, threshold, and no insecticide) and four rates of paclobutrazol (0, 70, 105, or 210 g ha−1 applied monthly) were evaluated. Replicate experiments were conducted from April to November in both 2018 and 2019 on a mixed creeping bentgrass and annual bluegrass fairway in North Brunswick, NJ. By the conclusion of both experiments, all paclobutrazol programs exhibited reduced annual bluegrass cover compared with the nontreated plots. In threshold and no-insecticide programs, reduction in annual bluegrass cover was enhanced by paclobutrazol applied at 105 g ha−1 in both years, and at 70 g ha−1 in the 2019 experiment. Paclobutrazol at 210 g ha−1 resulted in annual bluegrass cover of <20% regardless of insecticide program. In 2019, threshold-based ABW control without paclobutrazol provided similar annual bluegrass control as monthly applications of paclobutrazol at 70 and 105 g ha−1 with the preventive insecticide program. A reduction in turfgrass quality from threshold-based insecticide programs persisted for a shorter duration than the no-insecticide program, regardless of paclobutrazol treatment. Threshold-based ABW insecticide programs that allow ABW feeding damage to occur can result in reduced annual bluegrass cover. These reductions were further enhanced by paclobutrazol applications. The combination of threshold-level insecticide with moderate rates of paclobutrazol (70 to 105 g ha−1) provided reductions in annual bluegrass cover that were similar to the highest rate of paclobutrazol (210 g ha−1) without ABW damage. Turfgrass managers who integrate the threshold-level insecticide approach and monthly paclobutrazol applications may achieve greater annual bluegrass control than either strategy alone if temporary reductions in turf quality can be tolerated.

Immediate posttreatment irrigation has been proposed as a method to reduce hybrid bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt Davy] phytotoxicity from topramezone. Immediate irrigation is impractical, because it would take a turfgrass sprayer 10 to 15 min to cover an average golf course fairway or athletic field. There is also insufficient evidence regarding how posttreatment irrigation, immediate or otherwise, influences mature goosegrass [Eleusine indica (L.) Gaertn.] control from topramezone or low-dose topramezone plus metribuzin programs. We sought to investigate bermudagrass and E. indica response to immediate, 15-min, and 30-min posttreatment irrigation compared with no irrigation following topramezone at 12.3 g ae ha−1, the lowest labeled rate, or topramezone at 6.1 g ha−1 plus metribuzin at 210 g ai ha−1. We also evaluated placement of each herbicide and their combination on soil, foliage, and soil plus foliage to help elucidate the mechanisms involved in differential responses between species and herbicide mixtures. Responses were largely dependent on trial due to bermudagrass injury from high-dose topramezone being nearly eliminated by immediate irrigation in one trial and only slightly affected in another. When posttreatment irrigation was postponed for 15 or 30 min, topramezone alone injured bermudagrass unacceptably in both trials. Bermudagrass was injured less by low-dose topramezone plus metribuzin than by high-dose topramezone. All posttreatment irrigation timings reduced E. indica control compared with no posttreatment irrigation. The herbicide placement study suggested that topramezone control of E. indica is highly dependent on foliar uptake and that phytotoxicity of both bermudagrass and E. indica is greater from topramezone than metribuzin. Thus, posttreatment irrigation likely reduces topramezone rate load with a concomitant effect on plant phytotoxicity of both species. Metribuzin reduced 21-d cumulative clipping weight and tiller production of plants, and this may be a mechanism by which it reduces foliar white discoloration from topramezone.

Herbicide management information is lacking for recently developed turf-type bahiagrass germplasm. The objective of this study was to evaluate the herbicide tolerance of nine experimental bahiagrass genotypes compared to the industry standard ‘Argentine’. The experimental entries included Argentine and ‘Wilmington’ mutants, and wild-type breeding lines. Plants were grown under greenhouse conditions, and 12 herbicides were applied at 1× and 2× labeled rates. Bentazon, bromoxynil, carfentrazone + 2,4-D + MCPP + dicamba, and carfentrazone were classified as safe. Fluroxypyr, halosulfuron, and triclopyr + clopyralid reduced growth >50% when applied at twice the label rate. Fenoxaprop, sulfentrazone + imazethapyr, and thiencarbazone + iodosulfuron + dicamba reduced growth and caused turfgrass injury above an acceptable threshold (≥20%). In general, the Argentine mutants showed greater herbicide injury compared to the Wilmington mutants. However, metsulfuron exceeded the acceptable injury threshold and stopped growth in all the genotypes, Argentine and genotype WT6 were the least injured by this herbicide. The experimental genotype WT6 consistently showed the greatest herbicide tolerance. Except for one genotype (WT4), the experimental genotypes responded similarly or better than Argentine to the tested herbicides, except for metsulfuron.

Goosegrass [Eleusine indica (L.) Gaertn.] remains problematic for bermudagrass [Cynodon dactylon (L.) Pers.] turf managers due to the ineffective, selective control of mature plants with available postemergence herbicides and lack of sufficient residual activity from those herbicides to control seedling plants. Topramezone controls mature E. indica, but past efforts to suppress potential injury to bermudagrass turf have been inconsistent. We hypothesized that metribuzin at 210 g ai ha−1 in admixture with topramezone would improve bermudagrass tolerance while conserving mature E. indica control. In preliminary field studies, metribuzin mixed with topramezone at 1.2 or 2.5 g ae ha−1 applied twice at a 3-wk interval reduced bermudagrass injury and white discoloration compared with topramezone applied alone, but metribuzin did not safen bermudagrass to mesotrione. Topramezone at 3.7 g ha−1 plus 210 g ha−1 metribuzin applied twice at a 3-wk interval offered improved bermudagrass tolerance while it still controlled mature E. indica during 15 field and 2 greenhouse studies in Virginia. This program offered a 10-fold decrease in suprathreshold duration of white discoloration compared with topramezone alone at 6.1 g ha−1. Bermudagrass absorbed three times less radioactivity than E. indica at timings up to 48 h after treatment with [14C]topramezone. Bermudagrass also metabolized twice as much topramezone compared with E. indica at 48 h after treatment. Metribuzin reduced 14C absorption by approximately 25% in both species. These studies confirm the performance of a novel, low-dose topramezone plus metribuzin program for mature E. indica control in bermudagrass turf and suggest that selectivity between bermudagrass and E. indica to topramezone is due to differential absorption and metabolism. The fact that metribuzin reduces topramezone absorption in both species suggests that it may help reduce bermudagrass phytotoxic response to topramezone, but its role in altering selectivity between bermudagrass and E. indica may be due to other factors.

Topramezone and carfentrazone + 2,4-D + mecoprop-p + dicamba (SpeedZone®) are herbicides labeled for POST goosegrass (Eleusine indica L. Gaertn.) control in hybrid bermudagrass (Cynodon dactylon × C. transvaalensis Burtt Davy). Field research was conducted in Knoxville, TN, during 2019 and 2020 to evaluate goosegrass control and hybrid bermudagrass tolerance to these herbicides applied alone and in mixture. Treatments included topramezone (12.2 g ha–1), SpeedZone® [carfentrazone (33.6 g ha–1) + 2,4-D (1,029 g ha–1) + mecoprop-p (322 g ha–1) + dicamba (91 g ha–1)] and SpeedZone® + topramezone at 12.2, 6.1, 3.6, or 2.4 g ha–1. A nontreated control was included for comparison. Hybrid bermudagrass tolerance was assessed on four cultivars (‘Northbridge’, ‘Tifway’, ‘Tahoma 31’, and ‘TifTuf’) via visual ratings of turfgrass injury and assessments of normalized difference vegetation index (NDVI). At the termination of the experiment, SpeedZone® alone and in mixture with topramezone controlled goosegrass better than or equal to topramezone alone. Mixtures of SpeedZone® + topramezone reduced injury on all cultivars compared to topramezone alone, particularly when mixtures delivered ≤6.1 g ha–1 topramezone. Injury subsided on all cultivars by 28 d after treatment regardless of herbicide. Findings suggest that SpeedZone® can be mixed with topramezone at the rates tested herein to minimize hybrid bermudagrass injury from topramezone applications for goosegrass control.

Few options are available for controlling bermudagrass invasion of seashore paspalum. Bermudagrass and seashore paspalum tolerance to topramezone, triclopyr, or the combination of these two herbicides were evaluated in both greenhouse and field conditions. Field treatments included two sequential applications of topramezone (15.6 g ai ha−1) alone and five rates of topramezone + triclopyr (15.6 + 43.2, 15.6 + 86.3, 15.6 + 172.6, 15.6 + 345.2, or 15.6 g ai ha−1 + 690.4 g ae ha−1). Secondary greenhouse treatments included a single application of topramezone (20.8 g ha−1) or triclopyr (258.9 g ha−1) alone, or in combination at 20.8 + 258.9 or 20.8 + 517.8 g ha−1, respectively. Greenhouse and field results showed that topramezone applications in combination with triclopyr present opposite responses between bermudagrass and seashore paspalum. Topramezone increased bermudagrass injury and decreased seashore paspalum bleaching injury compared to topramezone alone. In field evaluations, topramezone + triclopyr at 15.6 + 690.4 g ha−1 used in sequential applications resulted in >90% injury to bermudagrass, however, injury decreased over time. Furthermore, sequential applications of topramezone + triclopyr at 15.6 + 690.4 g ha−1 resulted in >50% injury to seashore paspalum. Application programs including topramezone plus triclopyr should increase bermudagrass suppression and reduce seashore paspalum injury compared to topramezone alone. However, additional studies are needed because such practices will likely require manipulation of topramezone rate, application timing, application interval, and number of applications in order to maximize bermudagrass control and minimize seashore paspalum injury.

Goosegrass control options in bermudagrass are limited. Topramezone is one option that offers excellent control of mature goosegrass, but application to bermudagrass results in unacceptable symptoms of bleaching and necrosis typical of hydroxyphenylpyruvate dioxygenase inhibitors. Previous research has shown that adding chelated iron reduced the phytotoxicity of topramezone without reducing the efficacy of the herbicide, resulting in safening when applied to bermudagrass. Our objective was to examine additional iron sources to determine whether similar safening effects occur with other sources. Field trials were conducted in the summers of 2016 to 2018 (Auburn University). Mixtures of topramezone and methylated seed oil were combined with six different commercial iron sources, including sodium ferric ethylenediamine di-o-hydroxyphenyl-acetate (FeEDDHA), ferrous diethylenetriamine pentaacetic acid (FeDTPA), iron citrate, FeSO4, and a combination of iron oxide/sucrate/sulfate, some of which contained nitrogen. Bermudagrass necrosis and bleaching symptoms were visually rated on a 0% to 100% scale. Reflectance (normalized difference vegetation index) and clipping yield measurements were also collected. Application of FeDTPA and FeSO4 reduced symptoms of bleaching and necrosis when applied with topramezone. Other treatments that contained nitrogen did not reduce injury but did reduce bermudagrass recovery time following the appearance of necrosis. Inclusion of small amounts of nitrogen often negated the safening effects of FeSO4. The iron oxide/sucrate/sulfate product had no effect on bleaching or necrosis. Data suggest that the iron source had a differential effect on bleaching and necrosis reduction when applied in combination with topramezone to bermudagrass. Overall, FeSO4 and FeDTPA safened topramezone the most on bermudagrass.

Annual sedge (Cyperus compressus L.) populations with resistance to halosulfuron were identified in turfgrass at two new locations in Georgia. Research was conducted to evaluate (1) resistance levels to two acetolactate synthase (ALS) inhibitors, (2) ALS enzyme susceptibility, (3) genetic differences associated with resistance, and (4) differential levels of ALS gene expression in these biotypes. In dose–response experiments, the biotypes were >160 times resistant to halosulfuron but only 12 times more resistant to imazaquin compared with a susceptible biotype. In vitro enzyme assays indicated that resistant (R) biotypes required 6.1-fold greater concentrations of imazaquin to reduce ALS activity 50% compared with the susceptible (S) biotype. Both R biotypes had a similar Pro-197-Ser amino acid substitution in the ALS gene that confers resistance to sulfonylureas. Compared with the S biotype, R biotypes had 4.4 times higher ALS gene expression than the S biotype. No differences in gene copy number were found between any biotypes for the ALS gene. Overall, ALS-resistant C. compressus selected by halosulfuron use in turfgrass may be exhibiting partial susceptibility to imazaquin but complete resistance to sulfonylureas. Differential levels of susceptibility to ALS inhibitors for these biotypes are associated with the Pro-197-Ser substitution and enhanced expression of the ALS gene.

Pinoxaden is a POST acetyl coenzyme A carboxylase (ACCase) inhibitor in the phenylpyrazolin chemical family and is labelled for turfgrass use at broadcast rates of 35.5 to 71 g ai ha−1 and spot spray rates of 156 to 310 g ai ha−1. A greenhouse rate-response study was conducted to characterize the efficacy of pinoxaden against common grassy weeds. Weed species examined in this study were yellow foxtail, southern sandbur, annual bluegrass, roughstalk bluegrass, large crabgrass, dallisgrass, bahiagrass, goosegrass, and perennial ryegrass. Nonlinear regressions were modelled to determine visible injury rates (the application rate at which 50% of the weed species were injured and the 90% [I90] rate) and weight reduction rates (the application rate at which there was a 50% reduction in fresh weight and 90% reduction [WR90]) for each weed species. Only annual bluegrass, bahiagrass, and goosegrass had visible injury I90 values greater than the maximum labelled spot spray rate of 310 g ai ha−1. Annual bluegrass, bahiagrass, southern sandbur, and goosegrass all had WR90 values greater than the maximum labelled spot spray rate of 310 g ai ha−1. Results from this study indicate that the evaluated weed species can be ranked, according to visible injury I90 values, from most to least susceptible: perennial ryegrass > yellow foxtail > dallisgrass > large crabgrass > southern sandbur > roughstalk bluegrass > bahiagrass > goosegrass > annual bluegrass.

Annual bluegrass (Poa annua L.) is a problematic annual weed in established turf where the intensive use of herbicides has resulted in the evolution of herbicide resistance. In 2017, 31 populations of P. annua suspected to be resistant to herbicides commonly used to control this weed in turf were collected from golf courses across southeastern Australia to check the resistance status to different herbicide groups. All populations were found to be resistant to multiple turf herbicides. Dose–response experiments confirmed resistance to propyzamide, simazine, rimsulfuron, foramsulfuron, endothall, and pinoxaden. Levels of resistance to rimsulfuron (>56-fold), foramsulfuron (>19-fold), endothall (>7-fold), and pinoxaden (>4.3-fold) compared with the susceptible population were high, but levels of resistance to propyzamide (>2-fold) and simazine (>2-fold) were lower. Considerable variation in resistance to endothall and pinoxaden was observed among the populations of P. annua. Target-site resistance was confirmed for acetolactate synthase and acetyl-CoA carboxylase inhibitors, but not for photosystem II and microtubule assembly inhibitors. This study documented the extensive resistance to herbicides in P. annua from turf in Australia. Three of the populations investigated exhibited multiple resistance to herbicides from five mechanisms of action. The identification of multiple-resistant P. annua on several golf courses is a serious concern for turf managers.