Annual Bluegrass Control Research Articles

Herbicide Programs for Annual Bluegrass (Poa annua L.) Control in Nebraska

Core Ideas Research done on annual bluegrass (ABG) control in other areas of the US are likely applicable to Nebraska. However, extreme weather can dramatically affect short‐term annual bluegrass cover and emphasize the need for long‐term control studies. Three fall POST applications of mesotrione plus prodiamine applied preemergence in August and/or November were effective for ABG control in Kentucky bluegrass fairways. Replacing mesotrione with ethofumesate was also effective when combined with prodiamine in August and November. June applications of bispyribac‐sodium at 4 oz/ac was highly effective for controlling ABG in creeping bentgrass fairways, and adding two more fall applications at the same rate improved control slightly, but there was no benefit to raising the rate to 6 oz/ac. Annual bluegrass (Poa annua L.) (ABG) is common in golf courses, and its control has been thoroughly researched in cool‐season turf east of the Mississippi River in the United States. However, ABG response to herbicides varies widely among environments and/or biotypes, and little ABG control research has been done in the northern Great Plains. Therefore, our objective was to validate ABG herbicide control systems in golf course fairways of Kentucky bluegrass (Poa pratensis L.) (KBG) or creeping bentgrass (Agrostis stolonifera L.) (CBG) in Nebraska. Preemergence (PRE) treatments of prodiamine or mesotrione were applied in late summer over 3 yr with or without fall postemergence (POST) treatments of mesotrione or ethofumesate for ABG control in a low‐mow KBG fairway. We also evaluated rate and frequency of bispyribac‐sodium applications with or without a late summer–applied PRE (dithiopyr) in early September for ABG control over 3 yr in a CBG fairway. Our research indicates that ABG control work done in other areas are likely applicable to Nebraska. Three fall POST applications of mesotrione plus prodiamine applied as a PRE in August and/or November was effective for ABG control in KBG fairways. Replacing mesotrione with ethofumesate was also effective when combined with prodiamine in August and November. June applications of bispyribac‐sodium at 4 oz/ac were highly effective for controlling ABG in CBG fairways, and adding two more fall applications at the same rate improved control slightly, but there was no benefit to raising the rate to 6 oz/ac. Lastly, extreme weather in one summer and one winter dramatically affected short‐term ABG cover and emphasized the need for long‐term control studies in areas with dramatic weather cycles.

Confirmation and Control of Annual Bluegrass (Poa annua) with Resistance to Prodiamine and Glyphosate

Poor annual bluegrass control was reported in golf course roughs following treatment with prodiamine (1120 gaiha−1) and glyphosate (840 gaeha−1) during hybrid bermudagrass dormancy. Research was conducted to determine if this annual bluegrass phenotype was resistant to both prodiamine and glyphosate and to determine the efficacy of herbicide mixtures for controlling this phenotype in the field. In PRE or POST dose-response experiments, 9 to 31 times more prodiamine or glyphosate was needed to control (or reduce dry biomass of) this resistant phenotype by 50% compared to an herbicide-susceptible phenotype. Moreover, glyphosate-susceptible plants accumulated 50% more shikimic acid (898 mgkg−1) 6 d after treatment than those resistant to glyphosate (394 mgkg−1). October (fall) applications of herbicide mixtures containing trifloxysulfuron, simazine,S-metolachlor, or mesotrione controlled this resistant annual bluegrass phenotype 84 to 98% in April (spring), with no differences detected among treatments. Our findings document the second instance of annual bluegrass evolving multiple resistance in a managed turfgrass system. However, several herbicide mixtures can be used to effectively manage this resistant phenotype.

Response of 110 Kentucky Bluegrass Varieties and Winter Annual Weeds to Methiozolin

Methiozolin is a new isoxazoline herbicide that has scarcely been tested in Kentucky bluegrass turf. A field trial was conducted in Blacksburg, VA, to determine response of 110 Kentucky bluegrass varieties and winter annual weeds to sequential fall applications of methiozolin. At 1.5 and 6 mo after initial treatment (MAIT), Kentucky bluegrass injury I30values (predicted methiozolin rate that causes 30% Kentucky bluegrass injury) ranged between 3.4 to more than 10 times the recommended methiozolin rate for annual bluegrass control. Methiozolin at all rates reduced cover of annual bluegrass, common chickweed, corn speedwell, hairy bittercress, mouseear chickweed, and Persian speedwell but increased cover of parsley-piert. For all varieties, methiozolin at 2 kg ai ha−1increased Kentucky bluegrass cover, turf quality, and turf normalized difference vegetation index (NDVI) relative to the nontreated check at 6 MAIT. Kentucky bluegrass relative cover change (RCC) was attributed primarily to weed control but was inversely correlated with methiozolin rates because of increased weed control and reduced Kentucky bluegrass growth. Despite the decline in RCC with increasing methiozolin rates, most Kentucky bluegrass varieties treated with the highest methiozolin rate (6 kg ha−1) still had greater Kentucky bluegrass cover than the nontreated check at 6 MAIT. Results from this study indicate that two fall applications of methiozolin at rates beyond that previously reported for annual bluegrass control can safely be applied to a broad range of Kentucky bluegrass varieties spanning most of the known genetic classifications.

Selective Broadleaf Weed Control in Turfgrass with the BioherbicidesPhoma macrostomaand Thaxtomin A

Both regulatory and consumer forces have increased the demand for biopesticides, particularly in amenity areas such as turfgrass. Unfortunately, few natural products are available for selective weed control in turfgrass. Two bioherbicides reported to control broadleaf weeds without injuring turfgrass arePhoma macrostomaand thaxtomin A. Field and container experiments were conducted to evaluate PRE and POST efficacy ofP. macrostomaand thaxtomin A on regionally important broadleaf weeds. In container experiments, PRE applications ofP. macrostomaprovided 65 to 100% control of dandelion, marsh yellowcress, and flexuous bittercress, equivalent to that of pendimethalin. Control of yellow woodsorrel, henbit, hairy galinsoga, common chickweed, or annual bluegrass was less than with pendimethalin. In contrast, POST applications did not control any species as well as an industry-standard synthetic auxin herbicide. PRE or POST applications of thaxtomin A controlled six of the eight species tested as well as the industry-standard PRE or POST herbicides. In field tests, overall PRE broadleaf weed control withP. macrostomaand thaxtomin A peaked 4 wk after treatment at 64 and 72%, respectively, and declined afterward, suggesting that these bioherbicides possess short residuals and therefore must be reapplied for season-long control. Overall POST broadleaf weed control usingP. macrostomaand thaxtomin A was only 41 and 25%, respectively. PRE followed by early-POST applications of thaxtomin A provided ≥ 86% henbit control. These results suggest that bothP. macrostomaand thaxtomin A are capable of controlling certain broadleaf weeds in turfgrass. However, both lack efficacy on some important weed species, particularly chickweed. Thaxtomin A efficacy on henbit was improved by increased dose and by PRE followed by early-POST applications.

Efficacy of the Bioherbicide Thaxtomin A on Smooth Crabgrass and Annual Bluegrass and Safety in Cool-Season Turfgrasses

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

Growth Stage Influences Mesotrione Efficacy and Fate in Two Bluegrass (Poa) Species

Mesotrione provides PRE and early POST control of annual bluegrass during Kentucky bluegrass establishment from seed, but applications do not effectively control multitiller plants. The physiological effects of growth stage on efficacy and the basis of mesotrione selectivity between species is not well understood. The objectives of this research were to evaluate mesotrione behavior in these species at three growth stages: pretiller (3 to 5 leaves), 1-tiller, and multitiller (5 to 7 tillers). In greenhouse experiments, a single mesotrione application at 280 g ai ha−1injured pretiller, 1-tiller, and multitiller annual bluegrass 54, 33, and 11% at 4 wk after initial treatment (WAIT), respectively. A sequential application of mesotrione increased injury to pretiller and 1-tiller annual bluegrass by 20 and 17% from a single treatment, respectively. Sequential mesotrione applications caused at least 14% injury to multitiller annual bluegrass and Kentucky bluegrass at all growth stages and did not reduce tillering compared to the nontreated. Annual bluegrass absorbed 34% more root-applied14C-mesotrione than Kentucky bluegrass in hydroponic culture, but relative differences (Bq g−1) among growth stages were not detected for both species. Averaged across growth stages, annual and Kentucky bluegrass absorbed 31 and 35% of the applied radioactivity after foliar treatments, respectively. However, averaged across species, multitiller plants metabolized approximately two times more14C-mesotrione than pretiller and 1-tiller plants. Overall, the selectivity of mesotrione for annual bluegrass control during Kentucky bluegrass establishment results from differential levels of root absorption. Mesotrione has limited efficacy for controlling multitiller annual bluegrass due to enhanced degradation compared to pretiller and 1-tiller plants.

Late Pre-Emergent Control of Annual Bluegrass with Flazasulfuron & Indaziflam

Late Pre-Emergent Control of Annual Bluegrass with Flazasulfuron & Indaziflam

Flumioxazin Tank-Mixtures with Six Herbicides for Annual Bluegrass (Poa annua) Control in Bermudagrass

Flumioxazin is a protoporphyrinogen oxidase inhibitor with potential for POST annual bluegrass control and PRE smooth crabgrass control in bermudagrass. However, flumioxazin applications are often less effective in winter, compared with fall, because of reduced efficacy on mature annual bluegrass. The objective of this research was to evaluate tank-mixtures of flumioxazin with six other herbicide mechanisms of action for POST annual bluegrass control in late winter and residual smooth crabgrass control. Flumioxazin at 0 or 0.42 kg ai ha−1was evaluated in combination with flazasulfuron at 0.05 kg ai ha−1, glufosinate at 1.26 kg ai ha−1, glyphosate at 0.42 kg ae ha−1, mesotrione at 0.28 kg ai ha−1, pronamide at 1.68 kg ai ha−1, or simazine at 1.12 kg ai ha−1. Flumioxazin alone controlled annual bluegrass 61 to 70% at 8 wk after treatment (WAT) in three experiments from 2012 to 2014 in central Georgia. Flumioxazin tank-mixed with flazasulfuron, glyphosate, glufosinate, pronamide, and simazine provided good (80 to 89%) to excellent (> 90%) control of annual bluegrass at 8 WAT in 2 of 3 yr. These tank-mixtures were also more effective than flumioxazin alone in 2 of 3 yr, and control was greater or equal to the tank-mix partners applied alone. Treatments that included flumioxazin provided excellent (≥ 90%) control of smooth crabgrass at 6 mo after treatment in all 3 yr. Overall, tank-mixing flumioxazin with other herbicide chemistries may improve POST annual bluegrass control, compared with exclusive treatments, and effectively control smooth crabgrass in bermudagrass.

Evaluating Annual Bluegrass Herbicide Resistance Evolution in Golf Course Fairways

Annual bluegrass is one of the most diverse plant species in the world and is the most problematic winter annual weed in commercial turfgrass. Continuous application of the same herbicide mechanism of action for annual bluegrass control on golf courses has increased herbicide-resistant populations. The purpose of this research was to simulate six herbicide-use strategies to evaluate the risk of annual bluegrass resistance evolution to glyphosate. In a worst-case scenario of yearly glyphosate applications at dormancy, resistance evolved within 10 yr and was predicted to evolve in > 90% of populations by yr 20. When glyphosate was rotated on alternate years with a unique mechanism of action, resistance was delayed for 12 to 15 yr. Season-long control of annual bluegrass often requires multiple herbicide applications. Therefore, additional strategies were simulated in which glyphosate was applied at dormancy with combinations of PRE and/or POST herbicides at various timings. Resistance was most effectively delayed with a PRE application in late summer, a POST application in fall, and alternating glyphosate with a different POST option at dormancy. This delayed resistance by 25 yr and a 35% risk was predicted after 50 yr. Strategies utilizing three annual herbicide applications with unique mechanisms of action were more effective for controlling population growth compared to other strategies. Resistance was predicted to evolve within 35 yr for each of the strategies simulated. However, these results indicate annual bluegrass herbicide resistance can be managed by using an integrated herbicide program, rotating unique mechanisms of action as frequently as possible.

Annual Bluegrass Control on Putting Greens from Three or Four Years of Season‐long Applications of Herbicides or Plant Growth Regulators in Three States

Annual bluegrass (Poa annua L.) may be the most troublesome and studied weed on golf courses in the United States. Given the genetic variability of annual bluegrass and its ability to adapt to different environments, it is important to understand how control methods vary across environments or regions. Our objective was to evaluate seven season‐long regimes of herbicide or growth regulators for annual bluegrass control in creeping bentgrass (Agrostis stolonifera Huds.) putting greens over 3 or 4 years in three states in the midwestern United States. Depending on the product, applications were made as often as every 2 weeks from April through September. Effectiveness of treatments varied widely by location and time, with treatments most effective in Indiana and Nebraska. Paclobutrazol was the most effective plant growth regulator for annual bluegrass control, followed closely by flurprimidol. Intermediate at reducing annual bluegrass was flurprimidol + trinexapac‐ethyl and trinexapac‐ethyl was ineffective. Among herbicides, the now discontinued experimental cumyluron was most effective and four applications of bispyribac‐sodium at 2 oz/acre every 2 weeks in August and September was more effective than 1 oz/acre applied every 2 weeks from May through September or applications of cumyluron. Though a number of products will reduce annual bluegrass on golf greens, overall control was relatively low, reinforcing the need to maximize cultural practices before attempting chemical control. Furthermore, our results reinforce the importance of superintendents’ experimenting and refining treatment regimes in their specific location to maximize efficacy.

Safety of Sequential Fall Methiozolin Applications on Creeping Bentgrass Putting Greens

Methiozolin is an herbicide with preemergence (PRE) and postemergence (POST) activities for control of annual bluegrass (AB; Poa annua L.). Previous research reported that fall applications provide better control than spring applications when methiozolin is applied as a POST, and PRE application appears to show a higher degree of efficacy than POST applications. Preemergence application for AB control on creeping bentgrass (CB; Agrostis stolonifera L.) putting greens requires treatment starting in late summer to early fall, when CB greens are likely under summer stress. Three field studies were conducted to evaluate the safety of fall sequential methiozolin applications on CB greens. Treatments consisted of methiozolin at 0.22, 0.45, 0.67, or 0.89 lb a.i./acre applied 1, 2, or 4 weeks apart, totaling 1.78 to 2.01 lb a.i./acre per season. Phytotoxicity was consistently observed in one out of three studies but was at an acceptable level (≥6 on a scale of 1–9) in all evaluations. Methiozolin applications, regardless of rate or application interval, resulted in a consistent AB control up to 95% over the season, compared with the nontreated control. Results suggest that sequential applications of methiozolin in fall with the initial treatment starting in late summer to early fall may provide effective AB control with acceptable safety to CB putting greens.

Seashore Paspalum Tolerance to Amicarbazone at Various Seasonal Application Timings

Turfgrass injury from triazines has limited the use of photosystem II (PS II) inhibitors for weed control in seashore paspalum. Amicarbazone is a new PS II inhibitor with potential safety in seashore paspalum, but the effects of application timing on turf tolerance has received limited investigation. Field experiments were conducted in Griffin, GA to evaluate the tolerance of ‘Sea Isle 1’ seashore paspalum to amicarbazone applications in winter, spring, and summer. Seashore paspalum had minimal injury (< 5%) from amicarbazone treatments (98, 196, and 392 g ai ha−1) applied for annual bluegrass control in winter and spring. By 6 wk after treatment (WAT), amicarbazone at 392 g ha−1provided 78 and 90% annual bluegrass control in 2013 and 2014, respectively, and was similar to pronamide at 1,680 g ai ha−1. Amicarbazone at 196 g ha−1provided 71% control of annual bluegrass in 2014, but control was poor (< 70%) in 2013. Sequential amicarbazone applications at 98 g ha−1provided poor control in both years by 6 WAT. From six amicarbazone rates (up to 984 g ha−1) applied in summer, seashore paspalum required 510 and < 123 g ha−1for 20% turfgrass injury (I20) and 20% clipping reduction (CR20), respectively, whereas I20and CR20measured > 984 g ha−1for ‘Tifway’ bermudagrass. Overall, amicarbazone may be safely applied to seashore paspalum in winter, spring, and summer at rates and regimens evaluated. However, seashore paspalum may exhibit shoot growth inhibition up to 4 WAT, suggesting that end users should be cautious when using amicarbazone during active growth in summer.

Cultural and Chemical Practices for Quality Improvement of Overseeded Bermudagrass [Cynodon dactlyon (L.) Pers. × C. transvaalensis Burtt-Davy] and Annual Bluegrass (Poa annua L.) Suppression

Dormant bermudagrass (Cynodon dactlyon (L.) Pers. × C. transvaalensis Burtt-Davy) is overseeded with perennial ryegrass (Lolium perenne L.) to maintain green color through the fall and winter. Annual bluegrass (Poa annua L.) control is critical for overseeding success, as this weed can greatly decrease aesthetic quality and playability of turfgrass due to excessive seedhead production. Research was conducted to evaluate the influence of pre-seeding cultural practices (scalping, solid-tine aerification, vertical mowing, and vertical mowing plus scalping) on overseeding establishment. The effect of increasing overseeding rates of perennial ryegrass (111, 222, 444, and 888 kg pure live seed·ha−1; 100, 200, 400, and 800 lb·A−1) and roughstalk bluegrass (Poa trivialis L.) (55, 111, and 222 kg pure live seed·ha−1; 50, 100, and 200 lb·A−1) on annual bluegrass populations was also investigated. Additionally, plant growth regulators (PGRs) were evaluated for annual bluegrass seedhead suppression and turf injury. Mefluidide at 0.056 kg ae·ha−1 (0.05 lb ae·A−1), and paclobutrazol, flurprimidol, trinexapac-ethyl, and trinexapac-ethyl plus ethephon at 0.28, 0.42, 0.382, and 0.095 plus 3.82 kg ai·ha−1 (0.25, 0.37, 0.34, 0.085 plus 3.4 lb ai·A−1), respectively, were applied twice, sequentially with a four-week interval. Contrary to previous research, pre-seeding cultural practices did not improve overseeding success. Annual bluegrass density decreased with increasing perennial ryegrass overseeding rates from 50% in the non-overseeded to 14 to 17% when overseeded with rates up to 222 kg pure live seed·ha−1, and 4 to 8% when overseeded with rates between 444 and 888 kg pure live seed·ha−1. Roughstalk bluegrass overseeded reduced annual bluegrass density from 50% in the non-overseeded, to 7 to 13% when overseeded with 55, 111, or 222 kg pure live seed·ha−1, regardless of the overseeding rate. Overseeding bermudagrass with roughstalk bluegrass or perennial ryegrass increased turfgrass green cover during winter, especially 100 days after seeding. Paclobutrazol, flurprimidol, and trinexapac-ethyl were successful at suppressing annual bluegrass seedheads and were not injurious to perennial ryegrass. Mefluidide resulted in efficient annual bluegrass seedhead suppression; however, unacceptable turfgrass injury occurred in 2012.

Dormant Turfgrass Paint and Glyphosate Application Timing Effects on Annual Bluegrass and Tall Fescue Control

Excellent annual bluegrass control can be achieved with dormant glyphosate and glyphosate + Endurant treatments applied November through February. The addition of Endurant to glyphosate in early applications (November and December) increases tall fescue control.

Methiozolin and Cumyluron for Preemergence Annual Bluegrass (Poa annua) Control on Creeping Bentgrass (Agrostis stolonifera) Putting Greens

Methiozolin and cumyluron are experimental herbicides that are reported to control annual bluegrass PRE or POST; however, no studies have compared these new herbicides to currently-registered herbicides for annual bluegrass control on putting greens over multiple years. Studies were conducted on three Virginia putting greens for 2 yr to compare methiozolin and cumyluron each at two rates to bensulide and bensulide plus oxadiazon at labeled rates for effects on annual bluegrass and creeping bentgrass cover, turf injury, normalized difference vegetative index (NDVI), turf quality, and annual bluegrass seedhead suppression. Methiozolin, cumyluron, bensulide, and bensulide plus oxadiazon did not significantly injure creeping bentgrass putting green turf, reduce quality, or reduce NDVI. Only methiozolin at 500 or 750 g ai ha−1 and cumyluron at 8,600 g ai ha−1 reduced area under the progress curve (AUPC) for annual bluegrass cover following four treatments over 2 yr applied in spring and fall each year. A concomitant increase in creeping bentgrass cover AUPC was also observed from the three treatments that reduced annual bluegrass cover. Methiozolin also reduced annual bluegrass seedhead cover at least 85% 1 mo after spring treatments and more than all other treatments except cumyluron at 8,600 g ha−1 (66%). These studies suggest that single treatments of methiozolin in spring and fall will not rapidly control existing annual bluegrass but can slowly reduce populations over time, presumably by preventing new seedling emergence. Methiozolin and cumyluron appear to be more effective than currently available herbicides bensulide and bensulide plus oxadiazon for PRE annual bluegrass control and seedhead suppression on golf putting greens.

Dithiopyr Efficacy, Absorption, and Fate in Annual Bluegrass, Goosegrass, Smooth Crabgrass, and Tall Fescue

Dithiopyr provides pre‐ and early postemergence (POST) control of smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl] in tall fescue (Festuca arundinacea Schreb.), and may allow greater application flexibility in spring than other herbicides. Dithiopyr also provides preemergence (PRE) control of annual bluegrass (Poa annua L.) and goosegrass [Eleusine indica (L.) Gaertn.], but POST applications are ineffective and may result from differential physiological fate compared to smooth crabgrass. Experiments were conducted to investigate efficacy, absorption, distribution, and metabolism of dithiopyr in annual bluegrass, goosegrass, smooth crabgrass, and tall fescue. From seven dithiopyr rates, 1.18, 1.03, 0.76, and >4.48 kg a.i. ha−1 were required to reduce shoot mass 50% from the nontreated for annual bluegrass, goosegrass, smooth crabgrass, and tall fescue, respectively. In laboratory experiments, smooth crabgrass had ≈75% more kBq kg−1 following root absorption of 14C‐dithiopyr than annual bluegrass, goosegrass, and tall fescue after 72 h. All species recovered >90% of foliar‐absorbed 14C in the treated leaf after 72 h, with limited 14C recovery (≤5%) in roots and nontreated shoots. Metabolism of dithiopyr increased from 1 to 7 d after treatment (DAT) in all grasses. Final metabolism measured 69, 52, 33, and 27% of total 14C recovered in smooth crabgrass, goosegrass, annual bluegrass, and tall fescue, respectively. Results suggest relative herbicide concentration and greater metabolism is associated with dithiopyr selectivity for POST control of smooth crabgrass compared to other grassy weeds in turf.

Methiozolin Efficacy, Absorption, and Fate in Six Cool‐Season Grasses

ABSTRACTSelective annual bluegrass (Poa annua L.) control in cool‐season turfgrasses is difficult with postemergence herbicides currently available to practitioners. Methiozolin is a new isoxazoline herbicide that controls annual bluegrass in cool‐season turfgrasses but physiological effects attributed to selectivity have received limited investigation. Experiments were conducted to evaluate injury, absorption, translocation, and metabolism of methiozolin in six cool‐season grasses. The rate of methiozolin required for 50% injury (I50) to annual bluegrass and tall fescue (Festuca arundinacea Schreb.) measured 1.67 and 5.11 kg ha−1, respectively, but I50 values measured >6.72 kg ha−1 for creeping bentgrass (Agrostis stolonifera L.), Kentucky bluegrass (Poa pratensis L.), perennial ryegrass (Lolium perenne L.), and red fescue (Festuca rubra L. var. rubra) at 4 wk after treatment (WAT). Annual bluegrass required 69 h to reach 50% foliar absorption of 14C‐methiozolin while other species required ≥90 h. At 96 h after treatment (HAT), all species retained ≥83% of foliar applied 14C‐methiozolin in the treated leaf while 7 to 13% and <5% was distributed to nontreated shoots and roots, respectively. Grasses had similar root absorption of 14C‐methiozolin and distributed <25% to shoots at 72 HAT. Metabolism in leaves was not detected at 3 or 7 d after treatment in any species. Extraction was poor (<30%) from multiple solvents evaluated in root metabolism experiments, and metabolites could not be quantified. Although differences in absorption were detected, no metabolism in shoots and poor root extraction suggest that differential target site binding or fate in roots probably contribute to methiozolin selectivity for annual bluegrass control in cool‐season grasses.

Annual Bluegrass (Poa annua) Control in Glyphosate-Resistant Perennial Ryegrass Overseeding

‘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−1glyphosate in January and 140 g ha−1followed by an additional 140 g ha−1applied 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.I50values obtained 6 wk after treatment from injury data were 2.56, 2.64, 0.81, and 0.84 g ha−1glyphosate 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.

Flazasulfuron Tank Mixtures with Amicarbazone for Annual Bluegrass Control in Seashore Paspalum

Flazasulfuron may be safely applied to actively growing seashore paspalum (Paspalum vaginatum Sw.), but applications for annual bluegrass control in late winter or spring could be injurious. A 3-year field experiment was conducted to evaluate tank mixtures of flazasulfuron with amicarbazone at turf dormancy or partial greenup to determine if combinations could enhance annual bluegrass control and mitigate seashore paspalum injury compared to exclusive treatments. Single applications of flazasulfuron at 26 g a.i. ha−1 at both timings provided good (80 to 89%) to excellent (>90%) control of annual bluegrass in 2 of 3 years, while sequential applications provided ≥86% control at both timings in all 3 years. Tank mixtures of flazasulfuron at 26 g ha−1 plus amicarbazone at 196 g ha−1 significantly improved annual bluegrass control from flazasulfuron alone at 26 g ha−1 at both timings in 2 of 3 years. Amicarbazone tank mixtures did not improve annual bluegrass control from flazasulfuron at 52 g ha−1 alone at either timing. Late winter applications of amicarbazone at 196 g ha−1 alone provided poor annual bluegrass control (<70%) in 2 of 3 years while applications at turf greenup provided ≥88% control in all 3 years. Pronamide provided fair control (70 to 78%) and excellent control (≥90%) of annual bluegrass in 2 of 3 years when applied at dormancy or at greenup, respectively. All flazasulfuron treatments caused 36 to 54% injury when applied at greenup but single applications at dormancy caused 13 to 29% injury. Amicarbazone and pronamide alone never injured seashore paspalum greater than 17% at both application timings and treatments at greenup provided the best combinations of annual bluegrass control and turf tolerance.

Evaluation of Adjuvants on Flumioxazin Efficacy for Postemergence Annual Bluegrass and Residual Smooth Crabgrass Control

Evaluation of Adjuvants on Flumioxazin Efficacy for Postemergence Annual Bluegrass and Residual Smooth Crabgrass Control