Methiozolin is commonly used for the safe and selective removal of annual bluegrass from creeping bentgrass golf greens. Studies were conducted in 2013 and 2014 with the objective of assessing fertility programs consisting of synthetic fertilizers and biostimulants, with and without the plant growth regulator trinexapac-ethyl, to aid putting green canopy recovery following annual bluegrass removal via methiozolin. Additional studies were conducted to compare recovery of creeping bentgrass following an aggressive core aerification event with fertility programs with and without methiozolin. In all cases, the addition of 7 kg ha−1 of N-P-K from fertilizer or biostimulant biweekly to greens increased turfgrass recovery time by 1 to 3 wk compared to a standard green’s fertility program alone. Creeping bentgrass treated with biostimulants recovered equivalent to or quicker than creeping bentgrass treated with synthetic fertilizer (SF) in all cases. In the presence of methiozolin treatments, trinexapac-ethyl reduced time to 90% recovery (T90) by 0.25 to 0.5 wk at two locations, and increased T90 recovery time by 0.1 wk at one location. Otherwise, plots treated with SF plus trinexapac-ethyl were equivalent to plots treated with SF only. Methiozolin slowed turfgrass recovery time at one location where severe drought stress occurred but not at the other location that did not experience drought stress. These results suggest that turf managers should increase fertilizer treatments but will not need to discontinue trinexapac-ethyl use to maximize creeping bentgrass recovery following annual bluegrass control with methiozolin. These data also suggest that methiozolin has the potential to negatively affect creeping bentgrass recovery when drought stress is experienced.

Methiozolin is an isoxazoline herbicide that selectively controls annual bluegrass in cool-season turf and may control roughstalk bluegrass, another weedy Poa species that is problematic in many turfgrass systems. However, the majority of research to date is limited to evaluating methiozolin efficacy for annual bluegrass control in creeping bentgrass putting greens. Research was conducted comparing various application regimes of methiozolin and other herbicides for long-term roughstalk bluegrass control in creeping bentgrass golf fairways. Methiozolin-only treatments did not injure creeping bentgrass or reduce normalized difference vegetative index (NDVI) at 2 golf course locations based on 20 evaluation dates over a 2.5-yr period. The 2.5-yr average turf quality generally declined as roughstalk bluegrass control increased due to transient turf cover loss. At 1 yr after last treatment, methiozolin at 1500 g ai ha-1 applied four times in fall reduced roughstalk bluegrass cover 85%. This was equivalent to methiozolin at 1000 g ha-1 applied four times in fall, but greater than low rates of methiozolin applied four times in spring or twice in fall and spring. Amicarbazone, primisulfuron, and bispyribac-sodium alone either did not effectively reduce roughstalk bluegrass cover, or did so at the expense of increased creeping bentgrass injury. Results of this study suggest that methiozolin alone or tank-mixed with amicarbazone or primisulfuron is an effective long-term approach for selectively controlling roughstalk bluegrass in creeping bentgrass.

A field experiment was conducted over a 2-yr period to determine the effects of reduced PRE herbicide rates on large crabgrass infestation in six tall fescue cultivars. With the exception of oryzalin and benefin plus oryzalin in 1993, there was no cultivar by herbicide interaction for large crabgrass infestation when final ratings were made in 1993 and 1994. This interaction was caused by moderate to severe turfgrass injury that thinned the turf. When cultivars were disregarded, prodiamine was the only herbicide applied at one-third recommended rate in 1993 that effectively suppressed large crabgrass for the full season. Prodiamine and dithiopyr were the only PRE herbicides applied at one-third recommended rates for two consecutive years that effectively suppressed large crabgrass in 1994. Two-thirds recommended rate was needed for two consecutive years for oxadiazon, pendimethalin, oryzalin, benefin plus oryzalin, and benefin plus trifluralin to maintain optimum large crabgrass suppression in 1994.

A field study was conducted on tolerance of four seashore paspalum cultivars to postemergence (POST) herbicides in Georgia during 1995 and 1996. Quinclorac (0.8 kg/ha) and MON 12000 (0.07 kg/ha) at recommended rates were the only POST herbicides that did not affect the performance of any seashore paspalum cultivar (≥ 89%). When the rates were increased to three times recommended, the quality of ‘AP 10’ (≥ 96%) and ‘PI 28960’ (93%) cultivars was not affected, but the quality of ‘HI 25’ (≥ 84%) and ‘K-7’ (77%) was lower when compared with respective untreated plots. HI 25 recovered within 4 wk, but K-7 required 6 wk or longer. Dicamba at 1.7 kg/ha affected the quality of K-7 (69%) more at 2 wk than the other cultivars (85 to 92%). Diclofop, imazaquin, and 2,4-D plus mecoprop plus dicamba significantly reduced the quality of all cultivars 2 wk after treatment (WAT). The quality of all cultivars was similar at 2 WAT with diclofop at 1.1 kg/ha (79 to 84%). However, when treated with imazaquin at 0.4 kg/ha, the quality of K-7 (65%) was lower than AP 10 (85%), HI 25 (77%), and PI 28960 (81%), and when treated with 2,4-D plus mecoprop plus dicamba at 1.1 + 0.6 + 0.1 kg/ha, the quality of AP 10 (75%), PI 28960 (72%), and K-7 (57%) was lower than HI 25 (87%). POST applications of quinclorac, dicamba, and MON 12000 were safe to use for weed control in paspalum cultivars, whereas the safety of diclofop and imazaquin was marginal, and 2,4-D plus mecoprop plus dicamba was unacceptable.

Dithiopyr and prodiamine are new preemergence herbicides for crabgrass control in tall fescue and bermudagrass turf. A field experiment was conducted over a 2-yr period to determine the lowest rates of dithiopyr and prodiamine needed to control large crabgrass effectively in tall fescue and common bermudagrass. Prodiamine applied at 0.17 kg ai/ha in each of two applications controlled 92 to 93% of large crabgrass by late August in common bermudagrass and 78 to 85% in tall fescue. Dithiopyr applied at 0.11 kg ai/ha in each of two applications controlled 85 to 89% of large crabgrass in common bermudagrass, but the control was not consistent across years at any rate in tall fescue. Dithiopyr applied at 0.56 kg/ha on tall fescue controlled 91% of large crabgrass in 1993, but only 38% in 1994. The higher control with dithiopyr in common bermudagrass was due to greater competition with germinating large crabgrass seeds and emerging seedlings during the summer, compared with little or no competition from tall fescue. The quality of tall fescue and common bermudagrass treated with dithiopyr and prodiamine was generally higher in plots where large crabgrass was effectively controlled than in plots with poor control. In general, dithiopyr did not control large crabgrass as effectively in tall fescue as in common bermudagrass, while the control with prodiamine was similar for the two turfgrass species.

The tolerance of four established seeded common bermudagrass types to PRE and POST herbicides was evaluated. Pendimethalin at 3.4 kg ai/ha, oryzalin at 3.4 kg ai/ha, and dithiopyr at 0.8 kg ai/ha suppressed the quality of bermudagrass 8 to 16% more than oxadiazon at 4.5 kg ai/ha and prodiamine at 0.8 kg ai/ha. When interactions of PRE herbicide by bermudagrass cultivars occurred, oxadiazon, prodiamine, and pendimethalin suppressed the quality of ‘common’ and ‘Sahara’ 18 to 20% more than ‘Tropica’; oryzalin suppressed the quality of common and Sahara 11 to 18% more than Tropica; and dithiopyr suppressed the quality of common and Sahara 9% more than Tropic and ‘Cheyenne.’ The quality of Cheyenne treated with either oxadiazon, prodiamine, or pendimethalin was generally intermediate to the other cultivars. When POST herbicides by bermudagrass cultivar interactions occurred, MSMA plus metribuzin applied at 2.2 + 0.1 kg ai/ha injured common and Sahara an average of 10 to 12% higher than Tropica during 1993 and 1994. Diclofop applied at 1.1 kg ai/ha and dicamba applied at 0.6 kg ae/ha injured common 9 to 12% higher than Tropica. There was no difference in injury to cultivars when treated with 2,4-D plus mecoprop plus dicamba at 1.1 + 0.6 + 0.1 kg ae/ha. In general, Tropica was affected least by PRE and POST herbicide treatments, while common and Sahara cultivars were affected the most.

Oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] applied to bermudagrasses [Cynodon dactylon (L.) Pers.] at 4.5 kg ai/ha/yr in September reduced turf quality more than when treatments were applied anytime from April through August. The quality of ‘Tifway’ was reduced more than ‘Tifgreen’, ‘Tifdwarf’, or ‘Ormond’, and Ormond was reduced less than the other cultivars 3 weeks following oxadiazon treatment. Turf cover at the end of the growing season was not reduced with annual oxadiazon application at 4.5 kg/ha, whereas the cover was less in all plots treated with 13.5 kg/ha after four and five annual treatments. When compared with respective untreated cultivars, the cover of Tifway was reduced more from 13.5 kg/ha rate of oxadiazon than the other cultivars. Bermudagrass growth was retarded in the spring following oxadiazon applied the previous year.

Field experiments were conducted in 1989 and 1990 to evaluate the tolerance of ‘Penncross' creeping bentgrass and ‘Tifway’ bermudagrass fall-overseeded with perennial ryegrass to irrigation water containing simazine. Creeping bentgrass was more sensitive to simazine than the bermudagrass/ryegrass mixture. The predicted critical simazine concentration necessary to reduce creeping bentgrass quality ≤ 60% was 0.22 mg L–1 which corresponded to a cumulative simazine rate of 98 g ha–1. For bermudagrass/ryegrass, the predicted critical simazine concentration and cumulative simazine rate that reduced quality ≤ 60% was 0.68 mg L–1 and 306 g ha–1, respectively.

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 I30 values (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−1 increased 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.

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.