Knotroot foxtail has become more prevalent and problematic in pastures and hayfields in the southeastern United States. Gaps exist in our knowledge of which herbicide practices are best for managing this species in bermudagrass forage production. This study was conducted to determine the efficacy of various ways to control knotroot foxtail in bermudagrass with herbicide applications in autumn, postemergence (POST), with and without also applying a herbicide in preemergence (PRE), in spring. The study was a randomized complete block with a factorial arrangement of treatments and included a nontreated control for both fall and spring timings. Glyphosate at two rates (0.35 or 0.7 kg ae ha−1), nicosulfuron (0.07 kg ai ha−1) + metsulfuron (0.012 kg ai ha−1), and hexazinone (1.3 kg ai ha−1) were applied alone in the fall or followed by indaziflam (0.067 kg ai ha−1) or pendimethalin (4.46 kg ai ha−1) in the spring. Three harvests were conducted throughout the growing season to evaluate weed species (knotroot foxtail, large crabgrass, and horsenettle) and bermudagrass biomass as well as overall species composition. The combination of fall and spring treatments did not affect weed species or bermudagrass biomass. Therefore, treatment main effects were analyzed by fall or spring application timing. A spring application of either pendimethalin or indaziflam increased bermudagrass biomass compared with that of the nontreated control. However, neither PRE herbicide effectively reduced knotroot foxtail biomass compared with the nontreated control, although pendimethalin did reduce season-long knotroot foxtail composition. Spring PRE herbicides are an effective tool for forage producers, but further research is needed to identify effective herbicides and additional approaches for the control of knotroot foxtail.

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.

Sugarcane infested with bermudagrass and harvested as seed cane introduces the potential for weedy propagules to reinfest fields. Research was conducted in 2018 and 2019 following sugarcane harvest for seed cane to evaluate bermudagrass management with photosystem II (PSII)- and 4-hydroxyphenylpyruvate dioxygenase (HPPD)–inhibiting herbicides applied alone or mixed with triclopyr. Combinations of diuron at 2.8 kg ha–1 with clomazone at 1.5 kg ha–1 or triclopyr at 1.1 kg ha–1 and hexazinone at 0.74 kg ha–1 with triclopyr applied early POST (EPOST) in mid-February injured bermudagrass 85% to 86%, and injury was greater than diuron or hexazinone alone (16% and 10%) in mid-March. Bermudagrass injury decreased to 45% to 56% for these combination treatments by April; however, injury differences were similar to the earlier rating. Late POST (LPOST) mid-March application of these treatments indicated similar bermudagrass injury trends when evaluated in early April. By mid-May, however, no treatment resulted in greater than 18% bermudagrass injury. Clomazone plus diuron applied LPOST resulted in 19% sugarcane injury by early April; however, all other treatments resulted in 7% sugarcane injury or less. In mid-May, a mid-April EPOST application of topramezone at 0.025 kg ha–1 plus triclopyr at 1.1 kg ha–1 resulted in 62% bermudagrass injury, which was equivalent to that observed with other topramezone rates in this combination (0.012 and 0.037 kg ha–1) (54% to 60%). Bermudagrass injury from triclopyr mixed with mesotrione (32%) or triclopyr mixed with atrazine, mesotrione, and S-metolachlor (47% to 55%) resulted in bermudagrass injury similar to that with topramezone plus triclopyr (54% to 62%). Data showed the flexibility of triclopyr when mixed with several HPPD- or PSII-inhibitor herbicides for bermudagrass management in a Louisiana sugarcane cropping system. Greater flexibility in application timing for HPPD-inhibitor herbicides than for PSII-inhibitor herbicides (diuron or hexazinone), and mixed with triclopyr, may suppress bermudagrass POST in April and May with minimal sugarcane injury.

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.

POST goosegrass and other grassy weed control in bermudagrass is problematic. Fewer herbicides that can control goosegrass are available due to regulatory pressure and herbicide resistance. Alternative herbicide options that offer effective control are needed. Previous research demonstrates that topramezone controls goosegrass, crabgrass, and other weed species; however, injury to bermudagrass may be unacceptable. The objective of this research was to evaluate the safening potential of topramezone combinations with different additives on bermudagrass. Field trials were conducted at Auburn University during summer and fall from 2015 to 2018 and 2017 to 2018, respectively. Treatments included topramezone mixtures and methylated seed oil applied in combination with five different additives: triclopyr, green turf pigment, green turf paint, ammonium sulfate, and chelated iron. Bermudagrass bleaching and necrosis symptoms were visually rated. Normalized-difference vegetative index measurements and clipping yield data were also collected. Topramezone plus chelated iron, as well as topramezone plus triclopyr, reduced bleaching potential the best; however, the combination of topramezone plus triclopyr resulted in necrosis that outweighed reductions in bleaching. Masking agents such as green turf paint and green turf pigment were ineffective in reducing injury when applied with topramezone. The combination of topramezone plus ammonium sulfate should be avoided because of the high level of necrosis. Topramezone-associated bleaching symptoms were transient and lasted 7 to 14 d on average. Findings from this research suggest that chelated iron added to topramezone and methylated seed oil mixtures acted as a safener on bermudagrass.

South Texas is home to a high diversity of species due to its location at the confluence of subtropical, desert, and coastal ecoregions. Historical overgrazing of South Texas rangelands transformed the savanna and prairie to a landscape dominated by woody plants and shrubs interspersed with low seral grass species and bare ground. During the first half of the 20th century, exotic grass species, coupled with the application of industrial agricultural practices appeared to be the future of forage production in South Texas and elsewhere. Several of these exotic species, namely King Ranch bluestem [Bothriochloa ischaemum (L.) Keng], Kleberg bluestem [Dichanthium annulatum (Forssk.) Stapf], Angelton bluestem [Dichanthium aristatum (Poir.) C.E. Hubbard], buffelgrass [Pennisetum ciliare (L.) Link], guineagrass [Urochloa maxima (Jacq.) R. Webster], Lehmann lovegrass (Eragrostis lehmanniana Nees), and Bermudagrass [Cynodon dactylon (L.) Pers.], have escaped pasture cultivation. Additionally, the native grass tanglehead [Heteropogon contortus (L.) P. Beauv. ex Roem. & Schult.] has begun displaying invasive behaviors. The monoculture growth habit of these species simplifies vegetation structure, reduces biodiversity, and decreases habitat for many species of wildlife. These grasses also alter natural fire regimes and nutrient cycling. This landscape-level transformation of vegetation composition and structure requires monitoring to quantify and assess the spatial and temporal distributions of invasive species as a basis to inform management practices. Current advances in remote sensing technologies, such as very high spatial resolution coupled with daily satellite imagery and unmanned aerial vehicles, are providing tools for invasive vegetation monitoring. We provide a synthesis of the natural history of these grasses, including their introductions, an overview of remote sensing applications in South Texas, and recommendations for future management practices.

Bermudagrass is a major forage species throughout Georgia and the Southeast. An essential part of achieving high-yielding, top-quality forages is proper weed control. Indaziflam is a residual herbicide that controls many broadleaf and grass species by inhibiting cellulose biosynthesis. Research conducted in Tift and Colquitt counties in Georgia determined optimal PRE rates for indaziflam for bermudagrass forage production. Treatments applied at spring greenup of established ‘Alicia’ bermudagrass included indaziflam at 47, 77, 155, or 234 g ai ha−1 PRE, pendimethalin at 4,480 g ha−1 PRE, a split application of indaziflam at 47 g ha−1 PRE followed by the same rate applied POST after the first cutting, and a nontreated control (seven treatments in all). Forages were machine harvested three times each year for each location beginning at least 47 d after treatment (DAT), with final cuttings up to 168 DAT. For all treatments, fresh- and dry-weight yields at each harvest and totals for the season did not differ from the nontreated control. Indaziflam at 155 and 234 g ha−1 did cause minor stunting at 44 DAT, but this was transient and not observed at the second harvest. Indaziflam applied PRE has the potential to provide residual control of troublesome weeds in bermudagrass forage and hay production, with ephemeral stunting at the recommended application rates.

Field and greenhouse studies were conducted to evaluate annual bluegrass (Poa annua L. # POAAN) control and phytotoxicity of ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] to selected warm- and cool-season turfgrass species. Annual bluegrass control in non-overseeded dormant hybrid bermudagrass [Cynodon dactylon (L.) Pers. X C. tranvaalensis Burtt-Davy Tifgreen’ # CYNDA] was 75% or greater with at least two ethofumesate applications at monthly intervals starting in December. Tifgreen bermudagrass spring growth was delayed with more than two applications of ethofumesate at 1.1 kg ai/ha, or when the second application was made after January. Under greenhouse conditions the growth of both Tifgreen and Tifdwarf bermudagrass was less when treated with ethofumesate. Stand and shoot growth of 29 cultivars of ryegrass (Lolium spp.), bluegrass (Poa spp.), bentgrass (Agrostis spp.), and red fescue (Festuca rubra L. # FESRU) were reduced by ethofumesate at 1.1 kg/ha as a preemergence or split (0.5 kg/ha preemergence + 0.5 kg/ha postemergence) application. Postemergence applications were less phytotoxic to cool-season turfgrasses than preemergence applications. Perennial ryegrass stands were generally not reduced by postemergence application of ethofumesate at 1.1 kg/ha. However, shoot growth of perennial ryegrass was reduced.

For most producers, unmanned aerial vehicles (UAV) are a novelty that has been little employed in their agricultural operations. An UAV will not fix every problem on the farm, but there are some practical applications for which UAVs have demonstrated value. Three examples of how UAVs have been used in weed science applications are presented here; the methods are transferable to other agricultural commodities with similar characteristics. The first of these is quantification of the extent and severity of non-target herbicide injury. The second application is calculation of spray thresholds based on weed populations. The third application is development of site-specific herbicide treatment.

The presence of weeds during bermudagrass putting green establishment can reduce growth and turf quality. Three field experiments were conducted in Georgia to investigate efficacy of dimethenamid, S-metolachlor, and oxadiazon on the establishment of ‘TifEagle’ bermudagrass from sprigs. Dimethenamid at 0.85 and 1.7 kg ai ha−1, S-metolachlor at 1.1 and 2.2 kg ai ha−1, and oxadiazon at 1.1, 2.2, and 4.4 kg ai ha−1 did not reduce bermudagrass cover from the untreated after 8 wk. S-metolachlor at 4.4 kg ha−1 was the only treatment that reduced sprig cover from the untreated after 12 wk. All S-metolachlor and oxadiazon treatments provided excellent (≥ 90%) green kyllinga control by 8 wk after treatment (WAT) while dimethenamid at 0.85, 1.7, and 3.4 kg ha−1 provided 78, 85, and 92% control, respectively. Dimethenamid treatments provided poor control (< 70%) of spotted spurge but fair control (70 to 79%) was achieved from S-metolachlor at 4.4 kg ha−1 and oxadiazon at 2.2 and 4.4 kg ha−1 by 8 WAT. Overall, low to middle rates of the herbicides tested appear to temporarily inhibit TifEagle bermudagrass sprig establishment but high rates of dimethenamid and S-metolachlor may reduce cover from the untreated.

Field experiments were conducted in 1997 and 1998 to evaluate the effect of mowing followed by hexazinone for West Indian dropseed/giant smutgrass (Sporobolus indicus var. pyramidalis) (hereafter referred to as dropseed) control. The experimental design was a split plot, with mowing (nonmowed [mature] and 35-cm regrowth) as the whole plot and hexazinone rate (0.0 [control], 0.56, 0.84, 1.12, 1.40, and 1.68 kg ai/ha) as the subplot treatments. The application of 0.84 kg/ha hexazinone provided 94 and 81% dropseed control, 365 d after treatment (DAT) during 1997 and 1998, respectively. Increasing application rate to 1.12 kg/ha hexazinone provided 87 and 88% dropseed control, 365 DAT during 1997 and 1998, respectively. Both the 0.84 and 1.12 kg/ha rates provided the same average control (87.5%); however, the 1.12 kg/ha rate provided consistent control over years. Mowing dropseed, followed by hexazinone application at 35-cm regrowth, provided no additional control when compared with no mowing treatments. Rates of hexazinone at 1.40 and 1.68 kg/ha caused phytotoxicity to bahiagrass and increased bare soil surface area, especially 90 and 120 DAT. Phytotoxic effect on bahiagrass and on bare soil decreased 365 DAT, resulting in 75 to 80% total forage cover. Concentration and yield of total nonstructural carbohydrates were significantly lower for the mowed 35-cm regrowth treatment than for the nonmowed plants; however, even in its weakened condition this reduction had no effect on dropseed control.

Annual bluegrass is the most problematic winter annual weed in managed turfgrass. Acetolactate synthase (ALS)-inhibiting herbicides are effective for annual bluegrass control, but reliance on this mode of action can select for herbicide-resistant biotypes. Two annual bluegrass biotypes not controlled with ALS-inhibiting herbicides were reported at golf courses in South Carolina and Georgia. Research was initiated at Clemson University to verify the level of resistance of these biotypes to ALS inhibitors. Two ALS-susceptible (S) and suspected resistant (SCr, GAr) annual bluegrass biotypes were established in a greenhouse. Dose-response experiments were conducted on mature annual bluegrass plants using trifloxysulfuron, foramsulfuron, and bispyribac-sodium, all ALS-inhibiting herbicides. Additionally, a rapid diagnostic ALS activity assay was optimized and conducted using the same herbicides. For dose-response experiments, the rate of herbicide that reduced shoot biomass 50% (I50) values for the S biotypes were 13.6 g ai ha−1 for trifloxysulfuron, 7.0 g ai ha−1 for foramsulfuron, and 38.3 g ai ha−1 for bispyribac-sodium. Fifty percent shoot biomass reduction was not observed in either the SCr or GAr biotypes at eight times the labeled field rate of all ALS-inhibiting herbicides tested. For in vivo tests of ALS activity, the SCr biotype yielded I50 (concentration of herbicide that reduced ALS activity 50%) values 3,650, 3,290, and 13 times the S biotypes following treatment with trifloxysulfuron, foramsulfuron, and bispyribac-sodium, respectively. Similarly, I50 values for the GAr biotype were 316, 140, and 64 times greater than the S biotypes following the same herbicide treatments. This research indicates high levels of annual bluegrass resistance to multiple ALS-inhibiting herbicides in South Carolina and Georgia. Future research should focus on the mechanisms of ALS resistance in these annual bluegrass biotypes as well as alternative options for control not targeting the ALS enzyme.

Glyphosate is regularly used to control annual bluegrass populations in dormant bermudagrass turf. A population of annual bluegrass not controlled by glyphosate at 840 g ha−1 (glyphosate resistant, GR) was identified on a golf course in Humboldt, TN in 2010. Mature tillers of GR plants were established in a greenhouse and treated with glyphosate at 0, 210, 420, 840, 1,680, 3,360, and 6,720 g ha−1. Mature tillers of a biotype known to be susceptible to glyphosate (SS) were also established in the greenhouse and subjected to the same treatments. At 14 d after treatment (DAT), glyphosate controlled the SS biotype > 95% at rates > 420 g ha−1. Comparatively, the GR biotype was only controlled 76% with glyphosate at 6,720 g ha−1. The rates required to provide 50% control (I50 values) for SS and GR biotypes were 236 and 2,812 g ha−1 respectively, resulting in a resistance factor of 12. Photochemical efficiency (Fv/Fm) values on SS plants treated with glyphosate at > 210 g ha−1 measured 0.000 at 14 DAT, whereas Fv/Fm values on GR plants were not significantly different from the untreated control with glyphosate rates ≤ 840 g ha−1 on the same date. In laboratory experiments, the SS biotype accumulated greater shikimate concentrations than the GR biotype 3 to 6 DAT. Future research should evaluate strategies for managing GR and SS annual bluegrass with alternative modes of action.

Bermudagrass is grown extensively in the southern United States as a livestock forage. Annual grass weeds can be problematic in bermudagrass hay production, few effective control measures are available. Bermudagrass hay is harvested approximately every 28 d. Because most annual grass weeds germinate whenever environmental conditions become appropriate, control options must address a target weed population that varies in age, and may or may not have been mowed during previous harvests. Cohort age has rarely been included in control studies that combine herbicides and mowing. We tested this idea in a greenhouse study. Barnyardgrass, large crabgrass, and green foxtail were seeded on a weekly schedule. The following four treatments were initiated when five cohort ages ranging 8 to 36 d were obtained: clipping only, herbicide only, clipping followed by (fb) herbicide, and a nontreated control. Time interval between clipping and herbicide application was 5 d. Plants were clipped at 5 cm above the soil surface. Herbicide application was a tank mixture of nicosulfuron + metsulfuron at 39.3 + 10.5 g ai ha−1, respectively. Shoots were harvested 21 d after the herbicide treatment, and dry weights of the first three treatments were expressed as percent biomass reduction relative to the age-equivalent nontreated control. Regression analyses indicated a similar response pattern for all three grass species within treatments. For clipping alone, biomass reduction increased as cohort age increased. Conversely for herbicide alone, biomass reduction decreased with age. However, biomass reduction with the clipping fb herbicide treatment was only nominally influenced by grass cohort age, providing ≥ 84% biomass reduction across all cohort ages and species.

Research was conducted in 2003 and 2004 to evaluate diflufenzopyr tank mixes for western ragweed control and injury to ‘Tifton 85′ bermudagrass. In 2003 at 94 DAT, picloram at 0.28 and 0.56 kg ae ha−1 with or without diflufenzopyr provided greater than 95% control of western ragweed, whereas triclopyr + dilfufenzopyr, dicamba + diflufenzopyr, triclopyr alone, and diflufenzopyr alone provided < 77% control. In 2004 at 95 DAT, only the highest rate of picloram alone provided 96% control, and the two highest rates of picloram + diflufenzopyr provided at least 95% control. Tifton 85 bermudagrass growth reduction increased with the addition of diflufenzopyr to picloram in 2003, but not in 2004. However, forage dry-matter yield was not reduced by any herbicide treatment compared to the nontreated control. Results of these studies indicate that picloram alone and picloram + diflufenzopyr provide excellent control of western ragweed. The tank mixture of picloram + diflufenzopyr can improve control over picloram alone. However, dicamba + diflufenzopyr, triclopyr + diflufenzopyr, triclopyr alone, and diflufenzopyr alone did not provide adequate control.

Pesticide sorption by soil is among the most sensitive input parameters in many pesticide-leaching models. For many pesticides, organic matter is the most important soil constituent influencing pesticide sorption. Increased fertility, irrigation, and mowing associated with highly maintained turfgrass areas result in constant deposition of organic material, creating a soil system that can change drastically with time. Changes in soil characteristics could affect the environmental fate of pesticides applied to turfgrass systems of varying ages. Sorption characteristics of simazine and S-metolachlor were determined on five soils from bermudagrass systems of increasing ages (1, 4, 10, 21, and 99 yr) and compared to adjacent native pine and bare-ground areas. Surface soil (0 to 5 cm) and subsurface soil (5 to 15 cm) from all sites were air-dried and passed through a 4-mm sieve for separation from plant material. Using a batch-equilibrium method, sorption isotherms were determined for each soil. Data were fit to the Freundlich equation, and K d (soil sorption coefficient) and K oc (organic carbon sorption coefficient) values were determined. Sorption and soil system age were directly related to organic matter content in the soil. Sorption of both herbicides increased with age of the soil system and was greatest on the surface soil from the oldest bermudagrass soil system. Herbicide sorption decreased at greater soil depths with lower organic matter. Greater amount of 14C–simazine sorbed to subsurface soil of the oldest turfgrass system compared to 14C–S-metolachlor. Results indicate that as bermudagrass systems age and accumulate higher organic matter levels increased herbicide sorption may decrease the leaching potential and bioavailability of simazine and S-metolachlor.

‘Replay' and ‘JS501’ perennial ryegrass cultivars have been conventionally bred for reduced sensitivity to glyphosate, potentially allowing the herbicide to be used for selective weed control in overseeded bermudagrass. Field experiments were conducted to evaluate optimal glyphosate application rate, regime (single and sequential applications), and timing for annual bluegrass control in bermudagrass overseeded with these cultivars. Additionally, greenhouse experiments were conducted to compare the sensitivity to glyphosate of Replay and JS501 to susceptible cultivars ‘Caddy Shack' and ‘Top Gun II' through log-logistic rate-response analysis. In field experiments, only two treatments resulted in > 90% annual bluegrass control and < 25% perennial ryegrass injury. These two treatments were a single application of 280 g ae ha−1 glyphosate in January and 140 g ha−1 followed by an additional 140 g ha−1 applied in January. Perennial ryegrass cultivars were compared using 50% inhibition (I50) values, i.e. 50% visible estimates of injury or 50% reduction in clipping weight. I50 values obtained 6 wk after treatment from injury data were 2.56, 2.64, 0.81, and 0.84 g ha−1 glyphosate for Replay, JS501, Caddy Shack, and Top Gun II, respectively. Replay and JS501 were similar in sensitivity to glyphosate and were up to four times more tolerant than Caddy Shack and Top Gun II across rating dates and data types.

Indaziflam is an alkylazine herbicide that controls annual grasses by inhibiting cellulose biosynthesis. Compared with other PRE herbicides like prodiamine, indaziflam has a longer half-life in soil (> 150 d), which may allow for greater flexibility with application timing. Research was conducted in 2010 in Tennessee and Georgia evaluating smooth crabgrass control efficacy with indaziflam applied at early PRE, PRE, and early POST timings on the basis of soil temperature. Regardless of application timing, all rates of indaziflam (35, 52.5, and 70 g ai ha−1) controlled smooth crabgrass 89 to 100%. Prodiamine at 840 g ai ha−1 applied PRE provided ≥ 99% smooth crabgrass control on all rating dates. Smooth crabgrass plant counts were significantly correlated (r = −0.961; p < 0.0001) with visual ratings of smooth crabgrass control at the end of the study. Application flexibility with indaziflam may benefit turf managers in scheduling herbicide applications for smooth crabgrass control in Tennessee and Georgia.

Indaziflam is an effective PRE herbicide for annual bluegrass control, but soil residual effects could inhibit spring turf establishment in treated areas. To test this hypothesis, field experiments were conducted to evaluate establishment of bermudagrass, centipedegrass, St. Augustinegrass, and zoysiagrass after fall indaziflam applications. Lateral spread of turfgrasses from plugs in summer generally had no meaningful differences from treatments. However, high indaziflam rates (70 and 140 g ai ha−1) had approximately two-fold more nonrooted stolons than the nontreated control while low rates (17.5 and 35 g ha−1), oxadiazon at 3360 g ai ha−1, and prodiamine at 840 g ai ha−1 were similar to the nontreated. Indaziflam at 70 g ha−1 and prodiamine applications in fall reduced sprig establishment of the four turf species from the nontreated control, but oxadiazon and low rates of indaziflam were similar. Bermudagrass establishment from seed was significantly reduced (20 to 50%) by indaziflam at 35 to 140 g ha−1, prodiamine, and oxadiazon, on several dates, but the low rate of indaziflam was similar to the nontreated at 10 wk after seeding. Overall, fall indaziflam applications at 17.5 to 35 g ha−1 appear safe on vegetative establishment of four warm-season turfgrasses in spring but reseeding bermudagrass in areas treated with rates > 17.5 g ha−1 may cause unacceptable delays in growth.