Deertongue is a perennial, warm-season grass, and is problematic in naturalized areas of golf courses due to limited control options. Research was conducted to evaluate several herbicides for deertongue control in naturalized areas consisting primarily of fine fescue. Greenhouse studies assessed 24 herbicide admixtures and indicated that fluazifop, glyphosate, imazapic, and thiencarbazone + iodosulfuron + dicamba (TID) reduced deertongue biomass by >80% at 10 wk after initial treatment (WAIT). Subsequent field trials were conducted on golf course naturalized areas. The first site was on a woodland edge and was partially shaded for 6 h each day, and the second trial site was 50 m away from the woodland edge and not subjected to more than 1 h of daily shade. At 9 WAIT, fluazifop at 420 g ai ha−1 applied once or three times at 3-wk intervals and topramezone at 37 g ai ha−1 applied thrice at 3-wk intervals injured fine fescue by ≤10% at both sites. Glyphosate applied at 1,120 g ae ha−1, imazapic at 105 g ai ha−1, and imazapic at 53 g ai ha−1 tank-mixed with glyphosate at 560 g ae ha−1 injured fine fescue by ≥50% under shaded conditions, whereas glyphosate alone did not injure fine fescue under sunny conditions. Fine fescue was completely recovered by 52 WAIT from injury following herbicide treatments, except for glyphosate-containing treatments at the shaded site and glyphosate + imazapic at both sites. At 52 WAIT, glyphosate-containing treatments and sequential applications of fluazifop controlled deertongue by ≥93% and reduced shoot density to ≤5 shoots m−2 averaged over both sites. Fluazifop at 420 g ha−1 applied thrice at 3-wk intervals selectively controls deertongue with excellent safety to fine fescue. Glyphosate also controls deertongue, but unacceptably injures fine fescue when managed under shaded conditions. Future research will assess how different light intensities influence fine fescue epicuticular wax deposits and associated response to glyphosate.

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

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

In the transition zone, turfgrass managers generally utilize the dormancy period of warm-season turfgrass to apply herbicides for managing winter annual weeds. Although this weed control strategy is common in bermudagrass [Cynodon dactylon (L.) Pers.], it has been less adopted in zoysiagrass (Zoysia spp.) due to variable turfgrass injury during post-dormancy transition. Previous research reported that air temperature could affect weed control and crop safety from herbicides. Growth-chamber studies were conducted to evaluate zoysiagrass response to glyphosate and glufosinate as influenced by three different temperature regimes during and after treatment. A field research study was conducted at four site-years to assess the influence of variable heat-unit accumulation on zoysiagrass response to seven herbicides. In the growth-chamber study, glufosinate injured zoysiagrass more than glyphosate and reduced time to reach 50% green cover reduction, regardless of the rate, when incubated for 7 d under different temperature levels. When green zoysiagrass sprigs were incubated for 7 d at 10 C, the rate of green cover reduction was slowed for both herbicides; however, green cover was rapidly reduced under 27 C. After treated zoysiagrass plugs having 5% green cover were incubated at 10 C for 14 d, glyphosate-treated plugs reached 50% green cover in 22 d, similar to nontreated plugs but less than the 70 d required for glufosinate-treated plugs. Zoysiagrass response to glyphosate was temperature dependent, but glufosinate injured zoysiagrass unacceptably regardless of temperature regime. Diquat, flumioxazin, glufosinate, and metsulfuron + rimsulfuron injured zoysiagrass at 200 or 300 growing-degree days at base 5 C (GDD5C) application timings, but foramsulfuron and oxadiazon did not injure zoysiagrass regardless of GDD5C. The relationship of leaf density to green turf cover is dependent on zoysiagrass mowing height, and both metrics are reduced by injurious herbicides. Research indicates that glufosinate injures zoysiagrass more than glyphosate, and the speed and magnitude of herbicide injury generally increase with temperature.

Mesotrione typically requires multiple applications to control emerged weeds in turfgrass. As it is absorbed by both foliage and roots, a controlled-release (CR) formulation could eliminate the need for multiple applications. Research was conducted to evaluate simulated-release scenarios that mimic a potential CR mesotrione formulation. A soluble-concentrate formulation of mesotrione was titrated to produce a stepwise change in mesotrione rates, which were applied daily to mimic predetermined release scenarios over a 3-wk period. CR scenarios were compared to a broadcast treatment of mesotrione at 280 g ai ha–1 applied twice at 3-wk intervals, and a nontreated. Mesotrione applied in three temporal-release scenarios controlled creeping bentgrass, goosegrass, nimblewill, smooth crabgrass, and white clover equivalent to the standard sprayed mesotrione treatment in every comparison. However, each CR scenario injured tall fescue two to seven times more than the standard treatment. Soil- and foliar-initiated repeat treatments were equivalent in most comparisons. Our data indicate that mesotrione applied in a temporal range to simulate controlled-release scenarios can deliver desired weed control efficacy comparable to sequential broadcast applications. More research is needed to elucidate proper timings and release scenarios to minimize turfgrass injury.

Some fineleaf fescues have demonstrated tolerance to glyphosate, and this broad-spectrum, nonselective herbicide would be a valuable tool for controlling various weeds in low-input turf areas. A study was conducted to evaluate tolerance of 56 fineleaf fescue varieties to glyphosate applied at 0.0, 0.4, 0.6, and 1.0 kg ae ha−1. The defunct 2003 National Turfgrass Evaluation Program fineleaf fescue variety trial at the Turfgrass Research Center in Blacksburg, VA, provided main plots on which glyphosate treatments were randomized independently on May 16, 2011, and June 26, 2013. Hard (HF) and sheep fescues (SF) were the most tolerant to glyphosate, followed by strong creeping red fescues (STC) and slender creeping red fescues (SLC). The most sensitive species was Chewings fescue (CH), most varieties of which were injured 50% to 65% per kilogram of glyphosate at 2 wk after treatment (WAT). At 8 WAT, 12 of 14 CH varieties were injured over 30% per kilogram of glyphosate, but predicted injury and normalized difference vegetation index (NDVI) of all varieties were acceptable at a more typical 0.5 to 0.7 kg ha−1 glyphosate rate. Nontreated seed head density of CH varieties ranged from 87 and 126 seed heads m−2 at 8 WAT compared with 2.8 to 42 seed heads m−2 from HF varieties. Glyphosate at 0.15 to 0.5 kg ha−1 eliminated 90% of seed heads regardless of fineleaf fescue variety. These data suggest that all fineleaf fescue varieties are inherently tolerant of glyphosate at rates at or below approximately 0.7 kg ha−1, but can be generally separated from most to least tolerant in the following order: HF, SF, STC, SLC, and CH.

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.

Plant growth regulators paclobutrazol and flurprimidol were evaluated for suppression of Poa annua spp. reptans, a perennial biotype of annual bluegrass, in a creeping bentgrass green. Paclobutrazol at 0.6 kg ai/ha applied on Mar. 15, followed by 0.3 kg/ha on Apr. 29, 0.6 kg/ha on Oct. 1, and 0.3 kg/ha on Nov. 12 for each of 2 yr suppressed P. annua spp. reptans 28% approximately 4 mo after the final treatment. When paclobutrazol was applied at 0.3 kg/ha in each of four applications during the same period, suppression was similar to that with the higher rate 1 and 2 mo after final treatment but declined to 7% by 4 mo. Suppression of P. annua spp. reptans from flurprimidol applied four times during each of 2 yr was 22 to 27% 1 mo after final treatment but no suppression was noted 2 mo after the final treatment. Maximum creeping bentgrass injury was less than 20% when either paclobutrazol or flurprimidol was applied in the spring. However, creeping bentgrass injury was approximately 30% in the fall when either chemical was applied in the spring and repeated in October at 0.6 kg/ha.

Two experiments were conducted over a two-year period for large crabgrass control in centipedegrass. The experiments were: (a) sequential applications of PRE and POST herbicides, and (b) POST herbicides applied as sequential or tank-mixed applications. Large crabgrass control was greater than 80% throughout the spring and summer when dithiopyr was applied PRE at 0.14 kg/ha late in February or when tank mixed at the same rate with sethoxydim at 0.11 kg/ha and applied POST in late May. Control was similar from a sequential program of dithiopyr applied PRE at 0.14 kg/ha in February and followed either by dithiopyr at 0.14 kg/ha or sethoxydim at 0.11 kg/ha as POST in early to mid-summer. Dithiopyr at 0.28 kg/ha as a POST application in late May did not control large crabgrass consistently. Control was > 80% for 6 to 8 wk when the POST dithiopyr treatment was repeated at the same rate 1 mo later. Sethoxydim applied POST controlled large crabgrass greater than 80% throughout the spring and summer when applied once at 0.22 kg/ha or twice at 0.11 kg/ha in each of two applications. Dithiopyr applied alone or with sethoxydim as sequential or tank-mixed treatments caused slight to moderate centipedegrass injury but was commercially acceptable (< 30%). However, injury from tank-mix herbicides was similar to either applied alone. Quinclorac severely injured (> 30%) centipedegrass, and 8 to 10 wk were required for recovery.

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.

Preemergence herbicides were applied at recommended and three times the recommended rates during 1995, 1996, and 1997 to eight established zoysiagrass (Zoysia spp.) cultivars. Oxadiazon was the only herbicide that did not significantly reduce the quality of any zoysiagrass cultivar. The zoysiagrass cultivars had intermediate tolerance to prodiamine and pendimethalin, while oryzalin, dithiopyr, and benefin plus oryzalin caused the highest injury. ‘Emerald’ and ‘Meyer’ cultivars were least affected by herbicide application. ‘Diamond,’ ‘El Toro,’ ‘Cavalier,’ and ‘Crowne’ showed moderate injury, while ‘Royal' and ‘Palisades’ had the greatest injury. When the performance of zoysiagrass cultivars was averaged across herbicides, turf quality in May was best for Meyer, El Toro, and Crowne. The quality of the majority of cultivars except for Royal improved during the summer and was similar to that of Meyer by late August both years.

The effects of five preemergence herbicides on turfgrass quality and control of crabgrass (Digitaria spp.) were measured to determine the influence of thatch on preemergence herbicide activity in Kentucky bluegrass (Poa pratensis L.) turf. Field applications of benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin -5-one], and prosulfalin {N-[[4-(dipropylamino)-3,5-dinitrophenyl] sulfonyl]-S,S-dimethylsulfilimine} to thatchy Kentucky bluegrass turf in spring caused injury that was apparent during periods of summer stress, while DCPA (dimethyl tetrachloroterephthalate) and bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] caused little or no injury. The same treatments on thatch-free sites revealed that only prosulfalin was injurious. Adsorption of benefin, bensulide, and DCPA from solution was greater by thatch than by soil; however, the mobility of these herbicides in undisturbed thatch profiles was greater than measured in undisturbed surface soil from thatch-free sites. Thus, turfgrass injury from preemergence herbicides on thatchy sites is due to at least two factors: the greater mobility of preemergence herbicides in thatch than in soil; and the inherent susceptibility of Kentucky bluegrass to injury from preemergence herbicides that come into direct contact with roots and other absorbing organs.

Preemergence (PRE) and postemergence (POST) herbicides were sequentially applied to common bermudagrass over a two-year period to determine the lowest herbicide rates required to maintain acceptable large crabgrass and goosegrass control. Large crabgrass control was consistently higher in late August when MSMA at 2.2 kg ha−1 was applied to plots previously treated with dithiopyr at 0.3 kg ha−1 (99%) in 1991, and either pendimethalin at 1.1 kg ha−1 (95%) or oxadiazon at 1.1 kg ha−1 (94%) in 1992 than when either herbicide was applied alone (≤ 79%). Goosegrass control was also higher in late August when MSMA plus metribuzin at 2.0 + 0.14 kg ha−1 was applied to plots treated with pendimethalin at 1.7 kg ha−1 (71%) in 1991, with oxadiazon at ≤ 2.2 kg ha−1 (≤ 89%) in 1992, and with dithiopyr at 0.4 kg ha−1 (≤ 96%) both years than when the herbicides were applied alone. Diclofop at 1.1 kg ha−1 applied alone as POST controlled ≥ 96% goosegrass throughout the two-year period.

Bermudagrass growing in a creeping bentgrass green is a severe problem where both grasses are grown. An experiment was conducted to determine the effects of multiple flurprimidol-herbicide applications on tolerance of bentgrass and on suppression of three bermudagrass cultivars in bentgrass. Application of 1.4 kg ai ha–1 flurprimidol on April 15 and 0.8 kg ha–1 repeated on June 1 injured creeping bentgrass 44% in 1988 and 22% in 1989. Bermudagrass was suppressed from the two flurprimidol applications until mid-June in 1988. Growth in 1989 was not influenced by number of applications since bermudagrass was suppressed only until late May. Application of 0.8 + 54 kg ai ha–1 flurprimidol plus siduron on April 15 and 0.4 + 27 kg ha–1 on June 1 injured creeping bentgrass 23 to 28% and suppressed bermudagrass until mid-July in 1988 and mid-June in 1989. Application of 0.8 + 1.7 kg ha–1 flurprimidol plus ethofumesate on April 15 and 0.4 + 0.8 kg ha–1 on June 1 injured creeping bentgrass 25 to 28% and effectively suppressed bermudagrass until late August in 1988 and late June in 1989. Application of 0.8 + 54 kg ha–1 flurprimidol plus siduron or 0.8 + 1.7 kg ha–1 flurprimidol plus ethofumesate applied in June or June and July to plots treated in April did not improve bermudagrass suppression. In most instances there was an inverse relationship between bermudagrass suppression and number of bermudagrass stolons. There were interactions between flurprimidol-herbicide treatments on bermudagrass cultivars on number of stolons but not on suppression.

A two-year experiment was conducted to determine if tank-mixes of postemergence (POST) herbicides would consistently control large crabgrass and goosegrass in common bermudagrass turf compared to herbicide alone treatments. Tank-mixes of MSMA plus quinclorac at 2.2 + 0.6 kg/ha effectively controlled large crabgrass (≥ 81%) for 10 to 11 weeks during 1993 and 1994. The control from MSMA plus dithiopyr at 2.2 + 0.3 kg/ha was higher during this period than when each herbicide was applied alone at the same rate. There was no increase in large crabgrass control from tank-mixes of MSMA and diclofop applied in a single application, when compared with two applications of MSMA applied at 2.2 kg/ha. Goosegrass control at 9 wk after tank-mixed treatments of MSMA (2.2 kg/ha) and diclofop (≥ 0.3 kg/ha) in 1994 was lower (12 to 28%) than when diclofop at 1.1 kg/ha was applied alone (85%). Tank-mixes of MSMA with quinclorac or dithiopyr did not control goosegrass. In general, common bermudagrass injury was no higher from herbicide combinations than when each was applied alone. An exception occurred at 1 wk after treatment in 1993 when common bermudagrass injury was higher from tank-mixes of MSMA plus diclofop at 2.2 + 1.1 kg/ha, than when either herbicide was applied alone.

Sequential applications of preemergence (PRE) and postemergence (POST) herbicides were applied over a two-year period for large crabgrass and goosegrass control in common bermudagrass. Large crabgrass control was better when prodiamine at 0.3 kg ai ha−1 or oryzalin at 0.8 kg ai ha−1 were applied in late February, and followed by MSMA at 1.1 kg ai ha−1 in June than when prodiamine (0.8 kg ha−1) or oryzalin (2.4 kg ha−1) were applied at recommended rates. Goosegrass control was better when prodiamine was applied at 0.3 kg ha−1 followed by MSMA plus metribuzin at 2.2 + 0.1 kg ai ha−1, or when oryzalin was applied at 1.7 kg ha−1followed by MSMA plus metribuzin at 1.1 + 0.1 kg ha−1 than when prodiamine was applied at 0.8 kg ha−1 or oryzalin was applied at 3.3 kg ha−1. There was no increase in goosegrass control when diclofop was applied in sequence after prodiamine or oryzalin compared to diclofop alone. POST applications of diclofop, MSMA, and MSMA plus metribuzin did not injure common bermudagrass more severely when applied to plots previously treated with prodiamine and oryzalin than with POST herbicides alone.

Paclobutrazol and flurprimidol were evaluated for suppression of a perennial subspecies of annual bluegrass in a creeping bentgrass green. Three applications of paclobutrazol in the spring (Mar. 17, Apr. 17, and May 17) followed by three applications in the fall (Oct. 2, Nov. 2, and Nov. 30) suppressed the perennial subspecies ≥ 72% at 3 wk after the final treatment. However, suppression was reduced to ≤ 57% by 4 mo after the final fall application. Flurprimidol applied in three spring and three fall applications did not suppress the perennial subspecies as effectively as paclobutrazol. Suppression was ≤ 47% at 3 wk after the final flurprimidol treatment and was only ≤ 20% by mid-March. Neither chemical injured creeping bentgrass greater than 20% in the spring. However, leaf discoloration injury from the initial October application ranged from 26 to 30% for paclobutrazol in 1993 and 21 to 28% for flurprimidol in 1994. When injury occurred in October it was temporary and the creeping bentgrass recovered within 3 to 4 wk. Paclobutrazol and flurprimidol applied in November did not injure creeping bentgrass.

Tank-mix combinations of PRE and POST herbicides were applied to control emerged large crabgrass and goosegrass in common bermudagrass turf. Large crabgrass control was better when MSMA at 2.2 kg ai ha-1 was tank mixed with either pendimethalin at 1.7 kg ai ha-1 (≤ 85%) or dithiopyr at 0.3 kg ai ha-1 (≤ 94%), when compared with MSMA at 2.2 kg ai ha-1 (≤ 50%) alone. When MSMA plus metribuzin at 2.2 + 0.14 kg ai ha-1 was tank mixed with pendimethalin in 1992, large crabgrass control was better (≥ 96%) than when MSMA plus metribuzin was applied alone (≤ 73%). Quinclorac applied alone at 0.8 kg ai ha-1 controlled ≥ 94% large crabgrass, but control with diclofop was 32%. There was no increase in control when either quinclorac or diclofop was tank mixed with any PRE herbicide. Methyl ester of diclofop applied alone at 1.1 kg ai ha-1 provided 97% control of goosegrass at one location, but control was ≤ 62% at two other locations. Goosegrass control was better when diclofop at 1.1 kg ha-1 was tank mixed with dithiopyr at 0.6 kg ha-1 (≥ 77%) than when either diclofop (≤ 62%) or dithiopyr (≤ 50%) was applied alone. Goosegrass control was consistently better across years from combinations of dithiopyr plus diclofop at 0.6 + 1.1 kg ha-1 (82%) than from combinations of MSMA plus metribuzin with dithiopyr (34%) or pendimethalin (53%). Common bermudagrass injury at Griffin-Spalding Golf Course in 1991 was higher at 1 wk after combination treatments of MSMA plus metribuzin with dithiopyr (46 to 54%) or pendimethalin (50%) than with MSMA plus metribuzin applied alone (26%). Injury from the combinations was higher from single MSMA plus metribuzin treatment for 4 wk. Similar results occurred at the Georgia Station in 1992 from combinations of dithiopyr with MSMA plus metribuzin.

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.

The adaptation of herbicides to control the encroachment of one warm-season grass into another species is an important management practice. A field study was conducted in Georgia to determine the rates and frequency of herbicide applications needed to suppress three seashore paspalum cultivars and determine what effects these treatments will have on three bermudagrass cultivars. MSMA plus triclopyr plus clopyralid applied at a total of 2.7 kg/ha in each of three applications for a cumulative total of 8.1 kg/ha effectively suppressed (> 70%) ‘Sea Isle 1’ and ‘Sea Isle 2000’ for 13 wk during 1998 and 1999 and ‘K-3’ during 1998. The suppression of K-3 in 1999 was 56%. The suppression was higher in all instances when MSMA was applied with triclopyr plus clopyralid than when it was not included (< 45%). Four-way combinations of MSMA plus 2,4-D plus mecoprop plus dicamba applied at a total of 5.3 kg/ha in each of three applications for a cumulative total of 15.9 kg/ha suppressed K-3 from 37 to 66%, Sea Isle 2000 from 55 to 66%, and Sea Isle 1 from 59 to 65% for 13 wk. The suppression of three paspalum cultivars at 13 wk from tank mixes of MSMA plus 2,4-D plus dicamba applied at a total of 4.5 kg/ha in each of three applications for a total cumulative of 13.5 kgsol:ha was 7 to 12% lower using the four-way combination treatments. Injury to the bermudagrass cultivars from herbicide treatments was not a problem. In some instances, all herbicides caused some degree of bermudagrass injury on selected dates of treatment. Maximum injury from the herbicides ranged from 18 to 40% for ‘common’ bermudagrass, 18 to 39% for ‘Tifway’ and 30% for ‘TifEagle’ bermudagrass. When injury occurred, bermudagrass recovery was within 1- to 2-wk following treatments.