Lambert B. McCarty

Differential Response of Five Bahiagrass (Paspalum notatum) Cultivars to Metsulfuron1

Bahiagrass is used for roadsides, pastures, and lawns in the southeastern United States mainly because of drought and nematode tolerance. Metsulfuron is a sulfonylurea herbicide, which selectively controls bahiagrass in bermudagrass. Certain cultivars of bahiagrass were observed to be tolerant to recommended rates of metsulfuron. Therefore, research was conducted to investigate the susceptibility of five major bahiagrass cultivars to metsulfuron applied at increasing rates to 42 g ai/ha. Five bahiagrass cultivars were evaluated: ‘Pensacola’, ‘Tifton-9’, ‘Argentine’, ‘Common’, and ‘Paraguayan’. Argentine, Common, and Paraguayan cultivars showed a four- to fivefold increased tolerance to metsulfuron compared with Pensacola. Because of yearly inconsistencies, results for Tifton-9 were inconclusive. Nomenclature: Metsulfuron; Argentine bahiagrass, Paspalum notatum Fluegge var. notatum ‘Argentine’; bermudagrass, Cynodon dactylon (L.) Pers; Common bahiagrass, Paspalum notatum Fluegge var. notatum ‘Common’; Paraguayan bahiagrass, Paspalum notatum Fluegge var. notatum ‘Paraguayan’; Pensacola bahiagrass, Paspalum notatum Fluegge var. saurae Parodi ‘Pensacola’; Tifton-9 bahiagrass, Paspalum notatum Fluegge var. saurae Parodi ‘Tifton-9’. Abbreviations: GR50, metsulfuron rate required to reduce regrowth to 50% of untreated; OM, organic matter; WAT, weeks after treatment.

Detecting Annual Bluegrass (Poa annua) Resistance to ALS-Inhibiting Herbicides Using a Rapid Diagnostic Assay

Abstract Annual bluegrass is the most problematic winter annual weed in managed turfgrass. Acetolactate synthase (ALS)-inhibiting herbicides are effective for annual bluegrass control, but reliance on this mode of action can select for herbicide-resistant biotypes. Two annual bluegrass biotypes not controlled with ALS-inhibiting herbicides were reported at golf courses in South Carolina and Georgia. Research was initiated at Clemson University to verify the level of resistance of these biotypes to ALS inhibitors. Two ALS-susceptible (S) and suspected resistant (SCr, GAr) annual bluegrass biotypes were established in a greenhouse. Dose-response experiments were conducted on mature annual bluegrass plants using trifloxysulfuron, foramsulfuron, and bispyribac-sodium, all ALS-inhibiting herbicides. Additionally, a rapid diagnostic ALS activity assay was optimized and conducted using the same herbicides. For dose-response experiments, the rate of herbicide that reduced shoot biomass 50% (I50) values for the S biotypes were 13.6 g ai ha−1 for trifloxysulfuron, 7.0 g ai ha−1 for foramsulfuron, and 38.3 g ai ha−1 for bispyribac-sodium. Fifty percent shoot biomass reduction was not observed in either the SCr or GAr biotypes at eight times the labeled field rate of all ALS-inhibiting herbicides tested. For in vivo tests of ALS activity, the SCr biotype yielded I50 (concentration of herbicide that reduced ALS activity 50%) values 3,650, 3,290, and 13 times the S biotypes following treatment with trifloxysulfuron, foramsulfuron, and bispyribac-sodium, respectively. Similarly, I50 values for the GAr biotype were 316, 140, and 64 times greater than the S biotypes following the same herbicide treatments. This research indicates high levels of annual bluegrass resistance to multiple ALS-inhibiting herbicides in South Carolina and Georgia. Future research should focus on the mechanisms of ALS resistance in these annual bluegrass biotypes as well as alternative options for control not targeting the ALS enzyme. Nomenclature: Bispyribac-sodium; foramsulfuron; trifloxysulfuron; annual bluegrass, Poa annua L.

‘Tifway’ Bermudagrass Growth Regulation with the Use of Trinexapac-Ethyl and Flurprimidol1

Studies were conducted for 12 wk from June 16 to September 8, 2003 and July 10 to October 4, 2004 with the objective of evaluating growth regulation, lateral regrowth, and injury of Tifway bermudagrass [Cynodon dactylon (L.) × C. transvaalensis Burtt-Davy Tifway] in response to two GA-inhibiting plant growth regulators, trinexapac-ethyl and flurprimidol. Trinexapac-ethyl was applied alone at 0, 0.052, and 0.104 kg ai/ha and flurprimidol alone at 0, 0.14, and 0.28 kg ai/ ha, plus all combinations. Applications were made every 3 wk for the duration of the study. Tifway bermudagrass clipping yield was reduced 33% and 54% by trinexapac-ethyl at 0.104 kg/ha at 4 and 8 wk after initial treatment (WAIT), respectively. Flurprimidol at 0.28 kg/ha reduced clipping yield 49% 8 WAIT. Lateral regrowth was reduced 20% 2 WAIT by trinexapac-ethyl at 0.104 kg/ha, and 26% 2 WAIT by flurprimidol at 0.28 kg/ha. Lateral regrowth was reduced 13% 4 WAIT by trinexapac-ethyl at 0.104 kg/ha, and 15% 4 WAIT by flurprimidol at 0.28 kg/ha. Overall, acceptable injury (<30%) was observed with a trinexapac-ethyl and flurprimidol tank mixture; however, this evaluation did not indicate an advantage in growth regulation when using a tank mixture of these products, compared to using them alone. Nomenclature: Flurprimidol; trinexapac-ethyl; Tifway bermudagrass, Cynodon dactylon (L.) × C. transvaalensis Burtt-Davy Tifway. Additional index words: Plant growth regulator, fairways, injury, clipping reduction, percent lateral regrowth, turfgrass. Abbreviations: GA, gibberellic acid; PGRs, plant growth regulators.

Nutrient allocation of 'TifEagle' bermudagrass as influenced by trinexapac-ethyl

ABSTRACT Inhibiting shoot growth of dwarf bermudagrass [Cynodon dactylon(L.) Pers. × C. transvaalensis Burtt-Davey] with a plant-growth retardant, trinexapac-ethyl (TE), may redirect nutrients and photosynthate away from leaf tissue to promote root growth and improve nutrient-use efficiency. Two greenhouse experiments evaluated three rates of TE, 0.025, 0.05, and 0.075 kg a.i. ha−1, applied every three weeks on ‘TifEagle’ bermudagrass for 12 weeks. Lysimeters constructed to United State Golf Association specifications were arranged in a randomized complete block design with four replications. Increased TE rates quadratically reduced clipping yield 38%–75%, improved turf quality 6%–13%, and enhanced chlorophyll concentrations 30%–70% over the untreated grass. Dry-root mass increased with TE rate 11%–37% after 12 weeks. Total clipping nutrients recovered from five sampling dates were reduced by approximately 50%, 85%, and 90% for turf receiving TE at 0.025, 0.05, and 0.075 kg ha−1 3 wk−1, respectively. Thatch (stolons and rhizomes) and roots had higher nitrogen (N) concentration and retention with increased TE rate, suggesting inhibited leaf growth increased N storage in belowground plant tissue. Overall, TE may effectively enhance turf quality, root growth, and nutrient-use efficiency of dwarf-type bermudagrasses. Chemical name used: trinexapac-ethyl, [4-(cyclopropyl-[α]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethylester].

Mowing and Nitrogen Influence Green Kyllinga (Kyllinga brevifolia) Infestation in Tifway Bermudagrass (Cynodon dactylon × C. transvaalensis) Turf1

Abstract: A field study evaluated the effects of green kyllinga establishment method (seed vs. stolon), two mowing heights (2.5 and 5.0 cm), and three nitrogen (N) rates (0, 24, and 49 kg/ha/mo) on green kyllinga infestation in ‘Tifway’ bermudagrass turf. The study was initiated in vigorous and newly established or “weak” bermudagrass turf in May 1997 and continued until December 1998. The green kyllinga area was measured periodically each year and plant dry weight (g/500 cm2) was calculated in December 1997 and 1998. In 1997, stolon established green kyllinga plots were twice as large as seeded plots in vigorous turf and four times larger in weak turf. Method of establishment, however, was less important in 1998 as seedling populations became more established. In weak turf, increasing N rate to 49 kg/ha/mo decreased green kyllinga spread by 50% in 1997 and by 40% in 1998 compared to no N. In vigorous turf, mowing height influenced green kyllinga infestation more than N. Low mowing height (2.5 cm) increased green kyllinga infestations nearly twofold in vigorous turf in 1997 and more than fivefold in 1998. Golf course fairways are often maintained at clipping heights shorter than 2.5 cm, and green kyllinga is a prevalent weed at these sites. Green kyllinga may gain a competitive advantage in bermudagrass turf at lower mowing heights. Nomenclature: Green kyllinga, Kyllinga brevifolia Rottb.; bermudagrass, Cynodon dactylon Burtt-Davey × C. transvaalensis L. Pers. Tifway. Additional index words: Turfgrass cultural practices, weed competition, weed ecology. Abbreviations: N, nitrogen.

Yellow Nutsedge (Cyperus esculentus) Management and Tuber Reduction in Bermudagrass (Cynodon dactylon × C. transvaalensis) Turf with Selected Herbicide Programs1

Abstract: A 4-yr field study was conducted to evaluate yellow nutsedge suppression in ‘Tifway’ bermudagrass. Herbicide programs included preemergence (PRE) applications of metolachlor (3.4 kg ai/ha) and postemergence (POST) applications of imazaquin (0.28 kg ai/ha) plus MSMA (2.2 kg ai/ha) or halosulfuron (0.07 kg ai/ha) plus MSMA (2.2 kg/ha). Herbicides were applied to the same plots each year. Yellow nutsedge shoot suppression and tuber numbers were determined each year. Suppression of yellow nutsedge shoots increased over the 4-yr period from <74% in 1993 to >83% by 1996 with two annual applications of imazaquin plus MSMA or halosulfuron plus MSMA. PRE metolachlor applications did not suppress shoot production in any year; nor did they enhance suppression from POST treatments. Sequential applications of halosulfuron plus MSMA and imazaquin plus MSMA increased shoot suppression by 17 to 24% at 3 mo after initial treatment (MAIT) compared to single applications. All treatments reduced tuber numbers (>60%) after 4 years compared to untreated plots. Nomenclature: Halosulfuron, methyl 5-{[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl-aminosulfonyl}-3-chloro-1-methyl-1-H-pyrazole-4-carboxylate; imazaquin, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid; metolachlor, [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide]; MSMA, monosodium salt of methylarsonic acid; yellow nutsedge, Cyperus esculentus L. #3 CYPES; bermudagrass, Cynodon dactylon Burtt-Davey X C. transvaalensis L. Pers. ‘Tifway’. Abbreviations: MAIT, months after initial treatment; POST, postemergence; PRE, preemergence; WAIT, weeks after initial treatment.

Comparison of Enzyme and Growth Characteristics in ALS-Inhibitor Susceptible and Resistant Annual Bluegrass (Poa annua) Biotypes

Abstract Acetolactate synthase–- (ALS-) inhibiting herbicides are frequently used to control annual bluegrass in managed turfgrass systems. Recently, the number of annual bluegrass populations resistant to these herbicides has increased on golf courses. Previous research involving annual bluegrass resistance to ALS inhibitors has included elucidating the mechanism of resistance and in vivo response of ALS to ALS-inhibiting herbicides. The purpose of this research was to generate baseline information on enzymatic parameters of resistant (R) and susceptible (S) annual bluegrass biotypes and further distinguish these biotypes by comparing vegetative growth and reproductive characteristics. The R biotype contained a mutation in the ALS gene resulting in a Trp574 to Leu amino acid substitution. Compared to the S biotype, the R biotype exhibited a 27- and 10-fold resistance to trifloxysulfuron at the whole-plant level and under in vitro conditions, respectively. No significant differences were observed in substrate concentration at one-half maximum rate of enzyme activity (pyruvate) or extractable ALS activity between biotypes, but the maximum rate of enzyme activity was higher for the R biotype. The feedback inhibition of ALS activity by the branched-chain amino acids was higher for the R biotype than the S biotype, with leucine, valine, and isoleucine inhibiting ALS activity 20, 6, and 4% more in the R biotype, respectively. The R biotype produced more inflorescences and seeds per plant in comparison with the S biotype, but relative growth rates between biotypes were similar at all harvest intervals. Our research provides baseline information regarding ALS enzyme response, vegetative growth, and reproductive characteristics of annual bluegrass biotypes resistant and susceptible to ALS-inhibiting herbicides. Nomenclature: Trifloxysulfuron; annual bluegrass, Poa annua L.

Kyllinga squamulata Control in Bermudagrass Turf1

Abstract: Kyllinga squamulata has become problematic in bermudagrass turf in recent years, probably related to shifts in herbicide use strategies. Preemergence and postemergence greenhouse and field herbicide studies evaluated K. squamulata control in bermudagrass turf. Excellent (≥90%) postemergence control at 6 wk after initial treatment (WAIT) followed single and sequential applications of imazaquin at 0.42 kg ai/ha, MSMA plus imazaquin at 1.12 + 0.42 kg ai/ha, and sulfentrazone at 0.56 kg ai/ha. In one of two experiments, unacceptable (>30%) bermudagrass injury occurred with imazaquin at 0.42 and 0.56 kg ai/ha and MSMA plus imazaquin at 1.12 + 0.42 kg ai/ha 1 wk after application; however, plots recovered fully by 2 wk. In the field at 18 WAIT, preemergence control of greater than 70% was obtained with a single application of oxadiazon at 1.12 or 2.24 kg ai/ha and sequential applications of 1.12 kg ai/ha each 8 wk apart. Sequential applications 8 wk apart of sulfentrazone at 0.28 followed by 0.28 kg/ha also provided greater than 70% preemergence control. In two greenhouse studies, oxadiazon at 2.24 kg/ha and sulfentrazone at 0.56 kg/ha provided greater than 90% preemergence control. Nomenclature: Imazaquin; MSMA; oxadiazon; sulfentrazone; cocks comb kyllinga (proposed common name), Kyllinga squamulata Thonn. ex Vahl; hybrid bermudagrass, Cynodon dactylon Burtt-Davey × C. transvaalensis L. Pers. ‘Tifway’. Abbreviations: fb, followed by, WAIT, weeks after initial treatment, WAT, weeks after treatment.

Response of ‘TifEagle’ Bermudagrass (Cynodon dactylon × Cynodon transvaalensis) to Ethephon and Trinexapac-ethyl1

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. Nomenclature: Ethephon, (2-chloroethyl)phosphonic acid; trinexapac-ethyl, 4-(cyclopropyl-[α]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester; annual bluegrass, Poa annua L.; TifEagle bermudagrass, Cynodon dactylon × C. transvaalensis. Additional index words: Dwarf bermudagrass, plant growth regulator, turf injury. Abbreviations: GA, gibberellic acid; PGR, plant growth regulator; TE, trinexapac-ethyl; WAIT, weeks after initial treatment.

Postemergence Tropical Signalgrass (Urochloa subquadripara) Control with Nonorganic Arsenical Herbicides

Tropical signalgrass (TSG) has become a serious weed problem in tropical and subtropical regions such as Florida in recent years in association with the ban of organic arsenical herbicide use in turf. The purpose of this research was to identify alternative POST herbicides that control TSG. Two field experiments were conducted in bermudagrass golf course fairways in south and central Florida in 2014 and 2015. Several nonorganic arsenical herbicide treatments controlled TSG. In the first experiment, treatments containing amicarbazone alone and in combination with other herbicides provided > 97% TSG control 12 wk after initial treatment (WAIT) in 2014 and 2015. These included a single application of amicarbazone at 0.49 kg ai ha−1, or sequential applications of amicarbazone at 0.25 kg ha−1 in combination with foramsulfuron at 0.04 kg ai ha−1, sulfentrazone + imazethapyr at 0.25 kg ai ha−1, thiencarbazone + foramsulfuron + halosulfuron at 0.14 kg ai ha−1, and thiencarbazone + iodosulfuron + dicamba at 0.18 kg ai/ae ha−1. In the second experiment, sequential applications of thiencarbazone + foramsulfuron + halosulfuron at 0.14 kg ha−1 in combination with either quinclorac at 0.84 kg ai ha−1 or metribuzin at 0.28 kg ai ha−1 provided ≥ 85% TSG control 12 WAIT in both years. Nomenclature: Amicarbazone; dicamba; foramsulfuron; halosulfuron; imazethapyr; iodosulfuron; metribuzin; quinclorac; sulfentrazone; thiencarbazone; bermudagrass, Cynodon dactylon (L.) Pers.; tropical signalgrass, Urochloa subquadripara (Trin.) R.D. Webster. En años recientes, Urochloa subquadripara (TSG) se ha convertido en un problema serio de malezas en regiones tropicales y subtropicales, como Florida, en asociación con la prohibición de uso de herbicidas de arsénico orgánico en céspedes. El objetivo de esta investigación fue identificar alternativas de herbicidas POST que controlen TSG. Se realizaron dos experimentos de campo en fairways de campos de golf con césped bermuda en el sur y centro de Florida en 2014 y 2015. Varios tratamientos con herbicidas con arsénico no-orgánico controlaron TSG. En el primer experimento, los tratamientos que contenían amicarbazone solo o en combinación con otros herbicidas brindaron > 97% de control de TSG 12 semanas después del tratamiento inicial (WAIT) en 2014 y 2015. Estos incluyeron una sola aplicación de amicarbazone a 0.49 kg ai ha−1, o aplicaciones secuenciales de amicarbazone a 0.25 kg ha−1 en combinación con foramsulfuron a 0.04 kg ai ha−1, sulfentrazone + imazethapyr a 0.25 kg ai ha−1, thiencarbazone + foramsulfuron + halosulfuron a 0.14 kg ai ha−1, y thiencarbazone + iodosulfuron + dicamba a 0.18 kg ai/ae ha−1. En el segundo experimento, aplicaciones secuenciales de thiencarbazone + foramsulfuron + halosulfuron a 0.14 kg ha−1 en combinación con quinclorac a 0.84 kg ai ha−1 o metribuzin a 0.28 kg ai ha−1 brindaron ≥ 85% de control de TSG 12 WAIT en ambos años.