Plant growth regulators (PGRs) improve turf color by inhibiting leaf growth and may reduce fertilization requirements of bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt‐Davy] golf greens by reducing nutrients removed through clipping collection. To test this hypothesis, growth, color, and nutrient allocation of ‘TifEagle’ bermudagrass maintained at 3.2 mm were investigated in field experiments conducted in Clemson, SC, from April to August in 2003 and 2004. Ammonium nitrate was applied at 6, 12, 18, or 24 kg N ha−1 wk−1 with a PGR, trinexapac‐ethyl {[4‐(cyclopropyl‐[α]‐hydroxymethylene)‐3,5‐dioxo‐cyclohexane carboxylic acid ethyl ester]} (TE), at 0 or 0.05 kg a.i. ha−1 3 wk−1 Turf required 18 to 24 kg N ha−1 wk−1 from May to June and ≤12 kg N ha−1 wk−1 from July to August to maintain acceptable color (≥7, 1–9 scale). Trinexapac‐ethyl initially caused discoloration but bermudagrass recovered and had color enhanced 10 to 25% from nontreated. Trinexapac‐ethyl reduced clippings 67% from nontreated while clippings, percentage of lateral regrowth, and aerification recovery increased with N rate. Bermudagrass treated with TE had similar root mass to nontreated but 5% greater stolon and rhizome mass, 18% higher chlorophyll concentration, up to 67% reduced lateral regrowth, and up to 38% reduced aerification recovery. Trinexapac‐ethyl reduced leaf N, P, K, Mg, S, and Fe concentrations 10 to 25% and increased rhizome concentrations 8 to 36%. Nutrients recovered through clippings were reduced ≈70% from TE applications while TE‐treated turf had increased N, P, K, Ca, Mg, S, Mn, and Fe retention in stolons and rhizomes. Overall, TE enhanced color while reducing nutrient translocation from rhizomes to leaves, thus increasing bermudagrass nutrient retention.

Amicarbazone has potential for selective annual bluegrass control in cool-season turfgrasses, but seasonal application timings may influence efficacy. To test this hypothesis, field experiments in New Jersey and Indiana investigated amicarbazone efficacy from fall or spring applications and growth chamber experiments investigated the influence of temperature on efficacy. Fall treatments were more injurious to creeping bentgrass and Kentucky bluegrass than spring applications, but fall applications were also more efficacious for annual bluegrass control. In growth chamber experiments, injury and clipping weight reductions were exacerbated by increased temperatures from 10 to 30 C on annual bluegrass, creeping bentgrass, Kentucky bluegrass, and perennial ryegrass. Results suggest that amicarbazone use for annual bluegrass control in cool-season turf may be limited to spring applications, but increased temperature enhances activity on all grasses.

Dwarf bermudagrass (Cynodon dactylon × C. transvaalensis Burtt‐Davy) and creeping bentgrass (Agrostis stolonifera L.) are planted for golf greens in the U.S. transition zone, but management regimes, such as the use of a plant growth regulator (PGR), often vary for long‐term culture of the two species. The objective of this experiment was to investigate application regimens of the PGR trinexapac‐ethyl (TE), on growth, quality, and performance of creeping bentgrass and bermudagrass putting greens in Clemson, SC. ‘L‐93’ creeping bentgrass and ‘TifEagle’ bermudagrass putting greens, established in summer 2002 and mowed at 3.2 mm, received TE over 12 wk in three regimens: 0.017 kg ha−1 wk−1, 0.033 kg ha−1 2 wk−1 (biweekly), or 0.05 kg ha−1 3 wk−1 (triweekly) from May to August 2003 and 2004. Creeping bentgrass was not discolored from TE, but unacceptable bermudagrass discoloration (>20%) occurred on one, two, and six dates for weekly, biweekly, and triweekly regimens, respectively. All TE regimens reduced bermudagrass clippings approximately 50% from nontreated bermudagrass across all dates, while creeping bentgrass clipping reductions, approximately 20 to 35% from nontreated grass, were inconsistent. The root masses of both species treated with TE regimens were similar to nontreated turf. Bermudagrass aerification recovery was reduced on two, two, and four dates after weekly, biweekly, and triweekly TE regimens, respectively. All TE regimens increased morning and evening bermudagrass golf ball roll distance approximately 25 cm from morning distances of nontreated turf.

Methiozolin controls annual bluegrass in creeping bentgrass but application timing and temperature could influence efficacy in turf. In field experiments, sequential methiozolin applications totaling 3.36 kg ai ha−1provided excellent (> 90%) annual bluegrass control at 8 wk after initial treatment when treatments were initiated in February/March or May but programs totaling 0.84 and 1.68 kg ha−1provided poor control (< 70%) at both timings. Methiozolin at all rates caused minimal turf injury (< 8%) but creeping bentgrass was only injured from February/March applications. In growth chamber experiments, creeping bentgrass injury from methiozolin at 10 C was 2 and 4 times greater than at 20 C and 30 C, respectively, while annual bluegrass injury was similar across temperatures. In laboratory experiments, annual bluegrass had more foliar absorption of14C-methiozolin than creeping bentgrass at 30/25 C (day/night), compared to 15/10 C, but translocation was similar at both temperatures as > 90% of absorbed14C remained in the treated leaf after 72 h. Annual bluegrass distributed and recovered more radioactivity to shoots from root-applied14C-methiozolin than creeping bentgrass while both species had about 2 times more distribution to shoots at 30/25 C than 15/10 C. Metabolites were not detected in annual bluegrass or creeping bentgrass at 1, 3, or 7 d after treatment when grown at 15/10 C or 30/25 C suggesting uptake and translocation contributes to methiozolin selectivity in turfgrass.

Indaziflam controls annual grassy weeds by inhibiting cellulose biosynthesis. Research was conducted from 2008 to 2011 in Tennessee, Texas, and Georgia evaluating the efficacy of indaziflam for PRE and POST control of annual bluegrass in bermudagrass turf. In Texas, indaziflam at 30, 40, 50, and 60 g ai ha−1 applied PRE provided 93 to 100% annual bluegrass control through 28 wk after treatment. When applied PRE at 80 g ai ha−1 and at 4, 8, and 12 wk after PRE (WAP), indaziflam controlled annual bluegrass 67 to 100% 32 wk after initial treatment (WAIT) in Tennessee; however, reduced efficacy was observed with 12 WAP treatments in a single year of a 2-yr study. Similarly, annual bluegrass control with PRE applications or with 4 and 8 WAP applications of indaziflam at 35 and 52.5 g ai ha−1 ranged from 88 to 100% at 30 WAIT in Tennessee. In Georgia, these rates of indaziflam applied PRE and 4 WAP controlled annual bluegrass 96 to 100% on all evaluation dates and resulted in 97 to 100% reduction in plant counts relative to the untreated control at 30 WAIT. When applied 8 WAP, the 35 and 52.5 g ai ha−1 rates of indaziflam controlled annual bluegrass only 51 to 71% at 30 WAIT in Georgia. Although increasing the application rate of indaziflam treatments 8 WAP provided greater annual bluegrass control, each rate provided significantly lower control when applied 8 WAP compared with PRE or at 4 WAP. No bermudagrass injury was observed in this research. Results suggest indaziflam provides effective PRE and early POST control of annual bluegrass in bermudagrass turf. However, additional research is needed to determine the effects of plant size and maturity on indaziflam efficacy for POST annual bluegrass control.

Bispyribac-sodium is a POST herbicide that selectively controls annual bluegrass in creeping bentgrass, but inconsistent results with seasonal applications are believed to occur from temperature influences on bispyribac-sodium efficacy. Growth chamber experiments at the New Jersey Experimental Greenhouse Research Complex, New Brunswick, NJ, investigated three temperature regimes on ‘L-93’ creeping bentgrass and annual bluegrass responses to bispyribac-sodium. Annual bluegrass and creeping bentgrass exhibited contrasting responses to bispyribac-sodium as temperature increased from 10 to 30 C. Regressions of 4 week after treatment (WAT) data revealed as temperature increased from 10 to 30 C, required bispyribac-sodium rates for 50% clipping reduction (CR50) of annual bluegrass decreased from 85 to 31 g ai/ha and required rates for 50% leaf chlorosis decreased from greater than 296 to 98, indicating increased herbicidal efficacy at higher temperatures. In contrast, required bispyribac-sodium rates for creeping bentgrass CR50increased from 200 to greater than 296 as temperature increased from 10 to 30 C. Bispyribac-sodium discolored creeping bentgrass 0 to 20% at 20 and 30 C and discoloration increased 10 to 50% at 10 C. Thus, warmer temperatures (20 and 30 C) increase bispyribac-sodium efficacy for annual bluegrass control with minimal bentgrass discoloration; however, cooler temperatures (10 C) have minimal efficacy on annual bluegrass and increase bentgrass chlorosis.

Indaziflam is an alkylazine herbicide that controls annual grasses by inhibiting cellulose biosynthesis. Compared with other PRE herbicides like prodiamine, indaziflam has a longer half-life in soil (> 150 d), which may allow for greater flexibility with application timing. Research was conducted in 2010 in Tennessee and Georgia evaluating smooth crabgrass control efficacy with indaziflam applied at early PRE, PRE, and early POST timings on the basis of soil temperature. Regardless of application timing, all rates of indaziflam (35, 52.5, and 70 g ai ha−1) controlled smooth crabgrass 89 to 100%. Prodiamine at 840 g ai ha−1applied PRE provided ≥ 99% smooth crabgrass control on all rating dates. Smooth crabgrass plant counts were significantly correlated (r= −0.961; p < 0.0001) with visual ratings of smooth crabgrass control at the end of the study. Application flexibility with indaziflam may benefit turf managers in scheduling herbicide applications for smooth crabgrass control in Tennessee and Georgia.

Glyphosate is used in the transition zone to control annual bluegrass in fully dormant warm-season grasses. A suspected resistant (R) biotype of annual bluegrass was identified on a golf course in South Carolina after at least 10 consecutive years of glyphosate application. Greenhouse bioassays revealed the R biotype was 4.4-fold resistant to glyphosate compared with a standard susceptible (S) biotype. Further studies were conducted to investigate the mechanism conferring glyphosate resistance in the R biotype. Leaf discs of both biotypes accumulated shikimate in response to increasing glyphosate concentration, but the glyphosate concentration resulting in 50% EPSP synthase inhibition as a result of shikimate accumulation (I50) was 4.2-fold higher in the R biotype compared with the S biotype. At the whole plant level, similar levels of shikimate accumulation were observed between biotypes at 6 and 24 h after treatment (HAT) with glyphosate, but greater shikimate accumulation occurred in the S biotype at 72, 120, and 168 HAT. Shikimate levels decreased in the R biotype after 72 HAT. There were no differences in14C-glyphosate absorption between biotypes. However, more14C-glyphosate translocated out of the treated leaf in the R biotype and into root tissues over time compared with the S biotype. Partial sequencing of the EPSP synthase gene revealed a point mutation that resulted in an Ala substitution at Pro106. Although other mechanisms may contribute to glyphosate resistance, these results confirm a Pro106to Ala substitution is associated with resistance to glyphosate in the R annual bluegrass biotype.