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.

A study was conducted in 1994 and 1995 at two Mississippi locations to evaluate preplant incorporated (PPI) and preemergence (PRE) applications of alachlor, clomazone, SAN 582, metolachlor, pendimethalin, and trifluralin, and postemergence (POST) applications of AC 263,222 and imazethapyr alone or followed by clethodim late postemergence (LPOST) for red rice control in soybean. Applications of 110 g ai/ha clethodim increased red rice control when following any earlier herbicide application at one location that harbored a high natural infestation. In 1 yr at one location, red rice seedhead suppression from PPI and PRE herbicide applications alone was greater than 95% due to high activity from herbicides and drought conditions during red rice seedhead development. Early postemergence (EPOST) applications of 30 g ae/ha AC 263,222 suppressed at least 95% of red rice seedheads, regardless of year, location, or clethodim LPOST application. At one location, any treatment where 110 g/ha clethodim followed an earlier herbicide application suppressed red rice seedheads at least 95%. Compared to the nontreated control, only AC 263,222 injured soybean (30%) and reduced soybean yield (200 kg/ha).

A red fescue (Festuca rubra L.)- Kentucky bluegrass (Poa pratensis L.) turf was treated annually with amidochlor {N-[(acetylamino)methyl]-2-chloro-N-(2,6-diethylphenyl)acetamide} at 2.2, 2.8, and 3.4 kg ai/ha, mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} at 0.4 kg ai/ha, and ethephon [(2-chloroethyl) phosphonic acid] at 5.6 kg ai/ha for three consecutive years. Recuperative potential of treated turfgrass was determined in the field and in a greenhouse study. Amidochlor and mefluidide treatments injured turfgrass (11 to 64%) four weeks after application. However, turfgrass recovered after eight weeks. Amidochlor at 2.8 to 3.4 kg/ha and mefluidide at 0.4 kg/ha suppressed (75 to 100%) seedhead development. Ethephon at 5.6 kg/ha was ineffective. Turfgrass recovered normally each spring after amidochlor treatments, with no delay in spring green-up. Root length, root weight, and root:shoot weight ratio of the plugs from the greenhouse study were unaffected by three consecutive annual applications of amidochlor, mefluidide, and ethephon. One annual spring application of amidochlor, mefluidide, and ethephon for three consecutive years caused no adverse effects that would limit their use on red fescue-Kentucky bluegrass 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.

Research was conducted in 1990 through 1992 to examine the vegetative and reproductive growth regulating activity of imazaquin and AC 263,222 on common bermudagrass. AC 263,222 at 0.06 kg ha−1, alone and in combination with imazaquin (0.21 kg ai ha−1), significantly reduced seedhead number, seedhead height, and vegetative canopy height for a 4-wk period after both May and July treatment. Imazaquin (0.42 kg ai ha−1) applied alone resulted in less turfgrass discoloration, but suppressed vegetative and reproductive growth of common bermudagrass less as compared with treatments containing AC 263,222.

When centipedegrass was unmowed, seedhead suppression generally was better with imazethapyr than with mefluidide either alone or with flurprimidol, but these treatments were not effective for 8 weeks. In several instances, imazethapyr at 0.30 kg ai/ha and MH at 2.2 and 4.5 kg ai/ha severely injured (>30%) centipedegrass. Mowing weekly did not control seedhead development effectively, and none of the plant growth regulator plus mowing treatments effectively suppressed seedheads for 12 weeks. To effectively suppress seedhead production for 8 weeks, centipedegrass treated with mefluidide required mowing 3 weeks after treatment, while centipedegrass treated with imazethapyr or flurprimidol plus mefluidide required mowing at 3 and 6 weeks.

Clethodim was applied to tall fescue to determine the effects of application timing (fall, early spring, mid-spring), rate (0, 5.6, 11.2, or 22.4 g ai ha−1), and use of crop oil (0 or 2.3 L ha−1) on seedhead density and forage yield and quality of tall fescue. Increasing the rate of clethodim or adding crop oil reduced seedhead density and forage yield, and generally improved forage quality. There was no effect of application date in 1988 and 1990, but seedhead density and forage yield decreased from the November to the March application date in 1989.

Options for suppressing bermudagrass seedheads in managed turfgrass systems are limited. Experiments were conducted in 2009 and 2010 evaluating the use of fenoxaprop (25, 50, 75, and 100 g ha−1) for ‘Riviera’ bermudagrass seedhead suppression and growth regulation compared to imazapic (52 g ha−1), trinexapac-ethyl (91 g ha−1) and mefluidide (561 g ha−1). In field experiments, seedhead suppression ranged from 77 to 100% for fenoxaprop and imazapic at 35 d after treatment (DAT). Comparatively, seedhead suppression was < 25% for either trinexapac-ethyl or mefluidide at 35 DAT. Seedhead suppression was > 90% from 7 to 35 DAT for fenoxaprop applied at ≥ 50 g ha−1. Injury, determined visually, from fenoxaprop and imazapic in both the field and greenhouse measured < 25% on all rating dates, with no significant injury present after 21 DAT. In greenhouse experiments, fenoxaprop and trinexapac-ethyl showed similar reductions of bermudagrass growth; no differences in aboveground biomass were detected between these treatments at 42 DAT. Results of the current study illustrate that fenoxaprop and imazapic can be applied for bermudagrass seedhead suppression and growth regulation if moderate (< 25%) injury can be tolerated up to 21 DAT. Additional research is needed to evaluate the use of fenoxaprop and imazapic for seedhead suppression on other common and hybrid bermudagrasses.

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.

Field research was conducted to evaluate plant growth-regulator efficacy for tall fescue growth and seedhead suppression applied using application placement equipment. Specially designed equipment outfitted with fluid application systems applies low-volume plant growth regulator directly on plant foliage, reducing opportunity for drift and visible application. Wet-blade mowers are equipped to apply plant growth regulators and mow in a single pass, whereas rotary-wick applicators simply wipe chemicals directly on uncut vegetation. Therefore, a wet-blade, rotary-wick, and broadcast sprayer system were chosen to apply imazapic at three rates (9, 35, and 53 g ai/ha), and a mefluidide + chlorsulfuron tank mix at 7 + 140 g ai/ha to tall fescue roadsides for vegetative growth and seedhead suppression. Experiments were conducted during the spring and summer of 2004 in central and western North Carolina. Tall fescue was slightly injured and discolored by all treatments but fully recovered by 2 mo after treatment. Imazapic suppressed new vegetative growth 3 mo after treatment compared with the nonmowed–nontreated control (16.1 cm of growth) and the mowed–nontreated control (21.1 cm) when applied with the rotary-wick applicator (8.5 cm) and broadcast sprayer (6.2 cm). However, differences in vegetative height primarily occurred when application placement equipment treatments were compared with nontreated vegetation as opposed to mowed–nontreated plants. Although mowed–nontreated and wet-blade–treated plots had more new vegetative growth, nonmowed–nontreated plots still consistently had the greatest vegetative height. Seedhead suppression ranged from 87 to 100% when compared with the nonmowed–nontreated control, with wet-blade treatments consistently providing the least-effective seedhead suppression. Overall, application placement equipment did not improve plant growth-regulator efficacy when compared with the foliar broadcast spray.

Most tall fescue in the United States is infected with a fungal endophyte which imparts certain advantages to the plant, such as drought tolerance, insect feeding deterrence, and enhanced mineral uptake. However, the endophyte also produces ergot alkaloids that are harmful to livestock and contribute to fescue toxicosis. Because the alkaloids are concentrated in seed and stems, a potential way to reduce the likelihood of fescue toxicosis is by suppressing seedhead formation with herbicides. Research was conducted from 2012 to 2014 using metsulfuron applied alone and in combination with other herbicides in spring to determine the growth response of tall fescue, effects on forage quality, and ergot alkaloid concentration. Clipping or metsulfuron applied alone or in combination with aminocyclopyrachlor or aminopyralid reduced seedhead density by 36 to 55% compared to the nontreated control. Treatments containing metsulfuron reduced spring harvest yield 35 to 61%, but no differences were observed in the summer or year-after harvests. The same treatments increased crude protein levels by 1.03 to 2.14% and reduced acid detergent fiber levels by 1.60 to 2.76% compared to the nontreated control at spring harvest. Treatments containing metsulfuron reduced ergot alkaloid concentration 26 to 34% at the spring harvest, but no differences were observed in summer-harvested forage. Results from this study indicate metsulfuron applied alone or in combination with aminocyclopyrachlor or aminopyralid can potentially reduce the severity of fescue toxicosis and improve forage quality.

Experiments were initiated during 2003 and 2004 to evaluate application placement equipment for plant growth regulator (PGR) applications along bahiagrass roadsides. Recently designed equipment combine low-volume application and pesticide placement technology. Application placement equipment conceal the image of a traditional spray application. Evaluated application placement equipment included a wet-blade mower (Burch Wet Blade) and rotary-wick applicator (Weedbug™) compared with a traditional broadcast spray. Wet-blade mowers are designed to mow and simultaneously apply a pesticide solution to a cut stem or leaf in a single pass, whereas rotary-wick applicators are designed to wick a solution onto foliage. Evaluated PGRs included imazapic (9, 35, or 53 g ha−1) and sulfometuron-methyl (26 g ha−1). Bahiagrass injury varied with application placement equipment and was greater with rotary-wick applications in 2003, compared with foliar broadcast applications and the wet-blade mower. Bahiagrass seedhead suppression ranged from 31 to 60% with application placement equipment in July 2003 compared with 93% for a broadcast spray. In 2004, rotary wick- or broadcast-applied PGRs provided excellent (> 90%) seedhead suppression. Although application placement equipment may have advantages to broadcast-spray applications, evaluated equipment did not enhance bahiagrass suppression along roadsides in North Carolina compared with a foliar broadcast spray. Additional research is needed to determine if this type of application may provide consistent results with other species and compounds.

Options for suppressing zoysiagrass seedheads in managed turfgrass systems are limited. Experiments were conducted in 2010 and 2011 evaluating the use of imazamox (26, 52, and 70 g ai ha−1) or imazapic (52 g ai ha−1) for ‘Zenith' and ‘Meyer' zoysiagrass seedhead suppression. Imazamox and imazapic at ≥ 52 g ai ha−1 suppressed Zenith zoysiagrass seedheads ≥ 95% at 2 to 6 wk after initial treatment (WAIT) each year. Slight injury (< 10%) was observed with these treatments; however, effective seedhead suppression resulted in increased (i.e., darker) green color from 8 to 15 WAIT each year. Relative chlorophyll index values for imazamox- and imazapic-treated plots ranged from 100 to 147% of the nontreated control in 2010 and 89 to 125% of the nontreated in 2011. On Meyer zoysiagrass, imazamox and imazapic at ≥ 52 g ha−1 reduced seedhead counts greater than 90% in both Tennessee and Indiana. However, significant (> 25%) injury was reported with these treatments at one experimental location. Although imazamox and imazapic have efficacy for zoysiagrass seedhead suppression, additional studies are needed to determine factors affecting zoysiagrass injury potential from imazamox and imazapic applications.