Dinitroaniline herbicides are major herbicides used to control annual grass weeds in cool-season turfgrasses. At least three herbicides, benefin, pendimethalin, and trifluralin are labeled preemergence to control weeds in established turfgrass. Prodiamine could be a competitive product. Benefin at 2.2 to 3.4 kg ai/ha, pendimethalin at 1.7 to 3.4 kg ai/ha, prodiamine at 0.6 to 1.7 kg ai/ ha, and benefin plus trifluralin at 1.1 plus 0.6 to 2.3 plus 1.1 kg ai/ha effectively control many annual grass weeds, including large and smooth crabgrass, yellow and green foxtail, barnyardgrass, goosegrass, fall panicum, and annual bluegrass. Most dinitroaniline herbicides provide residual preemergence weed control for the entire growing season. In general, Kentucky bluegrass, perennial ryegrass, tall fescue, red fescue, and other cool-season turfgrasses tolerate most of these herbicides, although higher-than-normal rates of any dinitroaniline herbicide could restrict root growth and cause stand thinning in turfgrass species.

A study was conducted to evaluate effects of application timing and sulfometuron rate on weed control and bermudagrass tolerance. Sulfometuron was applied at rates from 13 to 105 g ai/ha and compared to 1120 g ae/ha 2,4-D amine. Control of Italian ryegrass and common vetch was not affected by October, November, December, or March application dates and 39 to 105 g/ha sulfometuron provided equivalent control of both species 6 mo after the initial treatment. Percent green cover of bermudagrass at 6 mo after the initial treatment was 22% or less following March applications compared to 36% or greater when applied in October, November, or December. More bermudagrass injury occurred following March treatments of 52 g/ha or greater sulfometuron where green cover was 14% and less compared to 22 and 30% green cover following 13 g/ha sulfometuron or 1120 g/ha 2,4-D amine, respectively.

CGA 163935 was evaluated for its growth regulating effect on common bermudagrass for two years and ‘Tifway’ bermudagrass for four years. The vegetative growth of mowed common bermudagrass was suppressed for 5 wk when CGA 163935 was applied at 0.2 kg ha–1 followed by 0.1 kg ha–1 2 wk later and mowed Tifway bermudagrass was suppressed for 4 wk after application of 0.2 kg ha–1. CGA 163935 suppressed vegetative growth of non-mowed common bermudagrass for 9 wk and non-mowed Tifway bermudagrass for 2 to 8 wk at the same rates. Common bermudagrass tolerated CGA 163935 when applied initially at 0.2 kg ha–1 and followed by 0.1 kg ha–1 at a 2-wk interval for a total 0.3 kg ha–1 rate. However, common bermudagrass was severely injured (> 30%) when CGA 163935 was applied at 0.2 kg ha–1 in each of two applications for a total rate of 0.4 kg ha–1. Tifway bermudagrass tolerated CGA 163935 when applied at 0.2 kg ha–1 as a single application or when the 0.2 kg ha–1 was followed by 0.1 kg ha–1 at a 4-wk interval. Tifway bermudagrass was severely injured (> 30%) when CGA 163935 was applied at 0.4 kg ha–1 as a single application or when 0.2 kg ha–1 was followed by 0.1 kg ha–1 at 2- or 3-wk interval. Seedheads were suppressed in common bermudagrass for 1 to 2 wk with CGA 163935 at 0.4 kg ha–1.

Plant growth regulators were evaluated on common and African ‘Tifway’ bermudagrass. Flurprimidol plus mefluidide applied at 1.1 plus 0.14 kg ha-1 and followed by 0.56 plus 0.14 kg ha-1 at 2- to 3-week interval suppressed vegetative growth of mowed common bermudagrass for 5 wk (17 to 23%) and unmowed turf for 6 wk (40%), but severely injured the turf. The injury ranged from 25 to 32% from 2 to 6 wk after treatment. The plant growth regulators that injured common bermudagrass less than flurprimidol plus mefluidide did not suppress the mowed turf for as long a period. Vegetative growth of common bermudagrass not mowed was suppressed for 6 wk when treated once with flurprimidol plus mefluidide and twice with flurprimidol, mefluidide, imazethapyr, paclobutrazol (1.1 plus 1.1 kg ha-1), and paclobutrazol plus mefluidide. Of the plant growth regulators evaluated, only imazethapyr suppressed common bermudagrass seedheads. The suppression was 70% for 4 wk, but reduced to <70% by 5 wk. Paclobutrazol applied initially at 1.1 kg ha-1 and followed at 0.56 kg ha-1 suppressed vegetative growth of mowed Tifway bermudagrass for 5 wk and unmowed turf for 8 wk without causing severe injury. The suppression of mowed Tifway bermudagrass with two applications of paclobutrazol was as good or better than with any other plant growth regulator. All plant growth regulators suppressed vegetative growth of unmowed Tifway bermudagrass for 8 wk.

Imazethapyr, glyphosate-isopropylamine salt, and glyphosate-sodium sesqui salt plus 2,4-D injured bahiagrass severely for 4 to 6 wk after treatment (WAT) but effectively controlled seedheads for 10 WAT without permanently reducing turf density. Imazethapyr applied twice at 0.08 kg ha-1 suppressed vegetative growth of mowed bahiagrass by 5 WAT while unmowed turf was suppressed 62% by 6 WAT. Glyphosate-isopropylamine salt suppressed vegetative growth by 3 WAT, but did not consistently suppress unmowed bahiagrass. Bahiagrass treated with glyphosate-sodium sesqui salt injured bahiagrass more than glyphosate-isopropylamine salt when each was applied at the same rate. CGA 163935 suppressed bahiagrass seedheads for 8 WAT and vegetative growth from 2 to 4 WAT. The activity of mefluidide, MON 4620 plus paclobutrazol, paclobutrazol plus mefluidide, and flurprimidol plus mefluidide was minimal on bahiagrass.

A mixture of bermudagrass with creeping bentgrass on golf greens results in a poor putting surface. An experiment was conducted to determine the frequency of herbicides applied alone or with flurprimidol on growth suppression of three bermudagrass cultivars and on tolerance of creeping bentgrass. Ethofumesate plus flurprimidol applied initially in mid-March or early April at 1.7 + 0.8 kg ha−1 and followed by four applications of 0.4 + 0.2 kg ha−1 beginning 6 wk later and then at 3-wk intervals, effectively suppressed bermudagrass growth throughout the growing season regardless of cultivar. Creeping bentgrass treated with ethofumesate plus flurprimidol at 1.7 + 0.8 kg ai ha−1 caused > 30% injury for 3 to 4 wk following application in 2 of 3 yr, but the turfgrass fully recovered. Injury was < 30% when ethofumesate plus flurprimidol was applied as repeated applications at 0.4 + 0.2 kg ha−1. Siduron plus flurprimidol applied initially in March or April at 54 + 0.8 kg ai ha−1 and followed by four additional applications at 14 + 0.2 kg ha−1 did not effectively suppress bermudagrass growth. Results with siduron alone at 54 kg ha−1 in March or April and repeated at monthly intervals at the same rate throughout the summer were similar to that obtained with siduron plus flurprimidol. Fenoxaprop applied at 0.07 kg ai ha−1 in early April and repeated at monthly intervals through August at the same rate effectively suppressed growth of common bermudagrass but did not suppress growth of Tifway or Tifgreen bermudagrasses. Creeping bentgrass was severely injured following fenoxaprop treatments.

During 1989 and 1990, herbicides were applied to suppress common bermudagrass in a mixed stand of common bermudagrass and ‘Emerald’ zoysiagrass. When the mixed stand was treated with fluazifop at 0.2 kg ha-1 mid-May and 0.1 kg ha-1 1 mo later for two consecutive years, the common bermudagrass cover was reduced from 35 to 7% and the zoysiagrass cover increased from 65 to 85%. Similar results were achieve when fenoxaprop was applied at 0.2 kg ha-1 mid-May and repeated at monthly intervals for a total of four applications each year for 2 yr. The quality of mixed common bermudagrass and zoysiagrass turf was reduced immediately after each treatment; however, zoysiagrass recovered and treatments did not result in permanent damage. Sethoxydim suppressed common bermudagrass during the second year of treatment, but reduced the zoysiagrass stand each year. Ethofumesate applied along or with flurprimidol severely reduced the zoysiagrass stand with an increase of common bermudagrass.

Glyphosate [N-(phosphonomethyl)glycine] consistently controls many winter annual weeds in dormant bermudagrass [Cynodon dactylon (L.) Pers.] but injures actively growing turf. Experiments were conducted to determine the effects of dates of glyphosate treatments on control of winter annuals in different stages of maturity and on the tolerance of bermudagrass when applied to the turf at different stages of greenness from dormant turf in the winter to actively growing turf in the spring. Glyphosate was applied at rates of 0, 0.3, 0.6, 1.1, and 2.2 kg/ha to different plots of winter annuals and bermudagrass at 3-week intervals from February 13 to May 3. Glyphosate at 0.3 kg/ha controlled at least 90% of annual bluegrass (Poa annua L.), spur weed (Soliva sessilis P. & K.), and corn speedwell (Veronica arvensis L.) within a 6-week period regardless of the date of treatment. All glyphosate treatments injured bermudagrass when applied to semi-dormant or actively growing turf. Bermudagrass treated with glyphosate at 0.3 kg/ha was injured the least and the turf had essentially recovered by 6 weeks after treatment. However, the injury from higher rates (0.6 to 2.2 kg/ha) was too severe to be acceptable in turf areas. Glyphosate did not severely injure bermudagrass when applied to dormant turf.

CGA 163935, paclobutrazol, and paclobutrazol plus mefluidide were evaluated for their growth regulating effect on centipedegrass over 3 yr. Paclobutrazol did not effectively suppress seedhead production or vegetative growth. Paclobutrazol plus mefluidide at 1.1 + 0.3 kg ai ha–1 in each of two applications at a 2-wk interval suppressed seedhead development 77% (average of 3 yr) at 10 wk after the initial treatment without severe injury or loss of stand, but duration of vegetative growth suppression was variable (0 to 6 wk). CGA 163935 applied at 0.4 kg ai ha–1 and followed by 0.2 kg ai ha–1 2 wk later suppressed vegetative growth of mowed and nonmowed centipedegrass for 10 wk, while suppressing seedhead production for 3 to 5 wk. CGA 163935 caused severe injury and stand loss of centipedegrass.

Pronamide was applied to a ‘Tifway’ bermudagrass golf green overseeded with perennial ryegrass during 1988 and 1989 to determine how herbicide rate and date affected ryegrass injury on transition back to a bermudagrass monostand. In most instances, perennial ryegrass was injured less when pronamide was applied at 0.28 or 0.56 kg ai/ha March 30 or April 13 than when application was delayed until April 28 or May 14. Perennial ryegrass injury lasted longer when 0.28 kg/ha was applied twice (March and/or April) than when applied singly at 0.28 kg/ha March 30 or April 13. The optimum time and rate of pronamide for effective transition was April 13 and 0.56 kg/ha, respectively.

Postemergence grass weed control in turf-type bermudagrass is currently available only with repeated applications of organic arsenicals and/or with combinations of metribuzin which decrease turf quality. Research was conducted to determine tolerance of the turf-type bermudagrass cultivars, Tifway, Ormond, and common, to diclofop rates ranging from 0.54 to 4.48 kg ai ha-1 with and without MSMA (2.2 kg ai ha-1) and metribuzin (0.2 kg ai ha-1). Bermudagrass cultivars tolerated diclofop well. When injury was evident, a rate response was noted, with higher rates (3.4 and 4.5 kg ha-1) resulting in increased phytotoxicity. However, this level of phytotoxicity was acceptable and the turf soon recovered (3 to 14 d). The addition of crop oil concentrate (1.25% v/v) did not affect turf quality. Addition of MSMA resulted in slightly lower turf quality than diclofop alone. However, these responses were acceptable and usually the turf recovered by 14 d after treatment. Metribuzin applied alone or in combination with diclofop damaged turf to unacceptable levels and up to 21 d were required for turf recovery.

Turf managers combine ethephon with trinexapac-ethyl (TE) on bentgrass greens to suppress annual bluegrass, inhibit turf growth, and enhance turf quality; however, effects of this growth regulator combination have not been reported on bermudagrass greens. Two experiments were conducted at the Clemson University Greenhouse Complex to investigate the response of ‘TifEagle’ bermudagrass to ethephon and TE. TifEagle bermudagrass plugs were placed in pots with 23-cm depths, 324-cm2 total surface areas, and a soil medium of an 85:15 (v/v) sand and peat moss mix. Ethephon was applied at 0, 3.8 (EP1), and 7.6 (EP2) kg ai/ha/3 wk with TE at 0 and 0.04 kg ai/ha/ 3 wk over a 9-wk period. Initial responses of bermudagrass to ethephon included chlorotic leaves and severe thinning. Bermudagrass treated with ethephon had quality reduced as much as 33% from nontreated turf. TE enhanced turf quality 4 to 22% from 4 to 9 wk after initial treatment. TE helped mask ethephon-induced quality decline after the third application. In the presence of TE, bermudagrass clipping yield was reduced from nontreated turf by 57, 70, and 72% when ethephon was applied at 0, 3.8, and 7.6 kg/ha/3 wk. Ethephon linearly reduced root mass after 9 wk from nontreated turf by 20 and 33% at 3.8 and 7.6 kg/ha/3 wk, respectively. Compared with respective ethephon rates alone, bermudagrass treated with TE and ethephon at 0, 3.8, and 7.6 kg/ha/3 wk, averaged 28, 8, and 15% more root mass. Ethephon at 3.8 and 7.6 kg/ha/3 wk without TE reduced TifEagle bermudagrass root length 14 and 16%, respectively, compared with untreated turf. Bermudagrass treated with ethephon at 0, 3.8, and 7.6 kg/ha/3 wk with TE averaged 3, 11, and 17% higher root length compared with respective ethephon rates after 9 wk. Overall, ethephon may have negative effects on TifEagle root mass, root length, and turf quality. However, combining ethephon with TE may help reduce these deleterious effects.

Aminocyclopyrachlor (AMCP) is a newly developed synthetic auxin herbicide for broadleaf weed control in turfgrass systems. AMCP has been observed to undergo rapid photodecomposition in shallow water when exposed to sunlight. Most herbicide applications on golf courses occur during the morning when dew is still present on the turfgrass canopy. These conditions could result in efficacy loss if photolysis occurred while AMCP is suspended in dew droplets. Research was conducted to determine the effect of ambient moisture on AMCP efficacy. AMCP (79 and 105 g ae ha−1), aminopyralid (280 g ae ha −1), and two AMCP granular formulations (84 g ha−1) were applied to dew-covered (WET) and dew-excluded (DRY) ‘Tifway' bermudagrass plots. Herbicide treatments applied to WET plots had greater visually rated bermudagrass injury than respective treatments applied to DRY plots at 7 and 21 d after treatment (DAT), with the exception of aminopyralid at 21 DAT. Normalized difference vegetative index on turfgrass quality complemented visual ratings, indicating greater turfgrass quality reductions when applied to WET vs. DRY plots. These results indicate that AMCP applications made to dew-covered turfgrass can increase herbicidal efficacy, and no significant losses due to photodegradation were observed.