Travis C. Teuton

Factors affecting seed germination of tropical signalgrass (Urochloa subquadripara)

Abstract Tropical signalgrass is one of the dominant weeds in the Florida turfgrass industry and is potentially troublesome for the southeastern turfgrass industry. Tropical signalgrass is especially problematic for St. Augustinegrass sod producers because of lack of control options. The objectives of our research were to determine the effect of light, pH, temperature, water potential, and planting depth on tropical signalgrass germination and emergence. Tropical signalgrass germination does not require light and is optimum at pH 5 to 6, temperature 25 C, and water potentials greater than − 0.4 MPa. Tropical signalgrass shoots emerged from depths of 0 to 7 cm, with maximum germination when placed on the soil surface. Tropical signalgrass seedlings emerged in the field during the second week of March in Ft. Lonesome, FL. Weekly mean soil and ambient air temperatures at the time of emergence were 20 C. Tropical signalgrass emergence was first observed at 118 and 73 growing degree-days (GDD) (13 C base temperature), with a peak emergence period at 222 and 156 GDD for 2001 and 2002, respectively. Nomenclature:  Tropical signalgrass, Urochloa subquadripara (Trin.) R. D. Webster BRASU; St. Augustinegrass, Stenotaphrum secondatum (Wait.) Kuntz.

Selection of Glyphosate-Resistant Annual Bluegrass (Poa annua) on a Golf Course

Abstract Annual bluegrass is a pervasive weed on golf courses in the Transition Zone of the United States and is difficult to selectively remove. For years, superintendents have applied glyphosate on dormant zoysiagrass to remove cool-season weeds. In 2007, a population of annual bluegrass in Columbia, MO, was not controlled with glyphosate after more than 10 yr of continuous applications. Greenhouse studies were established to compare the response of suspect glyphosate-resistant (CCMO1) and -susceptible annual bluegrass to glyphosate. Seedling plants were treated with glyphosate from 0 to 6.27 kg ae ha−1. At 21 d after treatment, reductions in biomass for susceptible annual bluegrass reached a maximum at glyphosate rates of 0.78 kg ha−1 or higher. Comparatively, the biomass of CCMO1 plants was only reduced by 50% at 0.78 kg ha−1, and reductions did not exceed 60% at rates up to 6.27 kg ha−1, which is eight times the labeled rate. At rates necessary to reduce plant dry weights by 50%, the resistance factor (RF) for CCMO1 was 5.2. Twenty-one days following biomass assessment, regrowth of plants was non-existent on susceptible plants at 0.78 kg ha−1 glyphosate or above, but CCMO1 plants reached 1.7 cm regrowth at the 6.27 kg ha−1 rate. Based on the regrowth, the RF for CCMO1 was 5.2. Results indicate a new species has been identified with resistance to glyphosate, and this represents the first report of glyphosate resistance in turfgrass. Nomenclature: Glyphosate; annual bluegrass, Poa annua L. POAAN; zoysiagrass, Zoysia japonica Steud.

Annual Bluegrass (Poa Annua) Control in Creeping Bentgrass (Agrostis Stolonifera) Putting Greens with Bispyribac-sodium

Annual bluegrass is one of the most difficult-to-control weeds in creeping bentgrass putting greens. Field trials were conducted in 2003 and 2005 to evaluate bispyribac-sodium for annual bluegrass management in creeping bentgrass greens maintained at a 3 mm mowing height. Bispyribac-sodium applied weekly at 12 or 24 g ai/ha controlled annual bluegrass 86% 12 wk after initial treatment (WAIT). In 2003, bispyribac-sodium applied at 12 and 24 g/ha/wk injured creeping bentgrass approximately 15 and 50% by 4 WAIT, respectively. However, injury was transient and was not evident by 12 WAIT. In 2005, the 12 and 24 g/ha/wk injured creeping bentgrass 15 and 85% by 8 WAIT, respectively, and was still evident throughout the trial. Putting green quality was reduced when compared to nontreated creeping bentgrass by the same treatments. The removal of annual bluegrass caused soil exposure until creeping bentgrass grew over the bare areas, contributing to decreased quality evaluations. Management of annual bluegrass in creeping bentgrass putting greens is possible with bispyribac-sodium. However, these results indicate bispyribac-sodium can cause excessive injury when applied to creeping bentgrass mowed at 3 mm. Nomenclature: Bispyribac-sodium; annual bluegrass, Poa annua L. POANN; creeping bentgrass, Agrostis stolonifera L. AGSST, ‘Penncross’.

Evaluation of oriental mustard (Brassica juncea) seed meal for weed suppression in turf.

Abstract Oriental mustard seed meal (MSM), a byproduct generated by pressing the seed for oil, exhibits herbicidal properties. In turfgrass, soil fumigants such as methyl bromide are used to control weeds prior to renovation of turf. Environmental concerns have resulted in deregistration of methyl bromide, prompting the need for alternatives. The objective of this research was to determine the effect of MSM on the establishment of selected turfgrass weeds as well as inhibitory effects on establishment of desirable turfgrasses. Greenhouse experiments were conducted in 2006 and 2007 at the University of Missouri. MSM was amended in soil at 0, 1,350 (low), 2,350 (medium), and 3,360 kg ha−1 (high) concentrations. Weed species included annual bluegrass, large crabgrass, buckhorn plantain, white clover, and common chickweed. Turfgrass species included: Rembrandt tall fescue, Evening Shade perennial rye, and Riviera bermudagrass. All species were seeded into soil amended with MSM and either tarped or left untarped. All treatments were compared to dazomet (392 kg ha−1), a synthetic standard. Plant counts and biomass of all species were recorded 4 wk after seeding. Overall, tarped treatments suppressed weed emergence 27 to 50% more compared to untarped treatments, except for large crabgrass. High rates of MSM suppressed emergence of all weeds ≥ 63%. Compared to the untreated control, the density of buckhorn plantain, white clover, and common chickweed was reduced by ≥ 42% at low rates of MSM. Biomass of buckhorn plantain, annual bluegrass, common chickweed, white clover, and large crabgrass was reduced from 37 to 99% at high rates of MSM. MSM at high rates reduced stand counts of tall fescue and perennial ryegrass up to 81% and 77% respectively, compared to the untreated control. Regardless of MSM rates or tarping, suppression of common bermudagrass emergence did not exceed 30%; tarped treatments actually increased bermudagrass emergence by 22%. The biomass for tall fescue, perennial ryegrass, and bermudagrass was reduced by 85, 68, and 10%, respectively, at high rates of MSM. For tall fescue, MSM at all rates strongly suppressed seed germination by 7 d after planting (DAP) (up to 100%), with additional germination observed through 14 DAP, but not thereafter. In both trials, dazomet completely suppressed emergence of all weeds. MSM appears to suppress emergence and growth of a number of weeds common in turf, with potential selectivity for bermudagrass. Nomenclature: Dazomet, tetrahydro-3,5-dimethyl-2H-1,3,5-thiadiazine-2-thione; glucosinolates (GSL); isothiocyanates (ITC); methyl isothiocyanate (MITC); Oriental mustard, Brassica juncea (L.) Czern.; annual bluegrass, Poa annua L. POAAN; buckhorn plantain, Plantago lanceolata L. PLALA; common chickweed, Stellaria media (L.) Vill. STEME; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; white clover, Trifolium repens L. TRFRE; ‘Evening Shade’ perennial rye, Lolium perenne L. LOLPE; ‘Rembrandt’ tall fescue, Festuca arundinacea Schreb. FESAR; ‘Riviera’ bermudagrass, Cynodon dactylon (L.) Pers.

Tropical signalgrass (Urochloa subquadripara) control with preemergence- and postemergence-applied herbicides.

Tropical signalgrass is one of the most serious weed problems in the St. Augustinegrass sod production in Florida, and its presence increases production costs and lowers turfgrass quality. The objectives of our research were to: (1) evaluate herbicides preemergence and postemergence for control of tropical signalgrass and (2) compare control of tropical signalgrass and other problem weeds (torpedograss, blanket crabgrass, and India crabgrass) with postemergence herbicides. In preemergence herbicide field trials, only benefin + oryzalin, imazapic, imazapic + 2,4-D, and oryzalin provided ≥75% tropical signalgrass control 8 wk after application (WAA). By 11 WAA, only benefin + oryzalin and imazapic + 2,4-D provided ≥75% tropical signalgrass control. In greenhouse experiments, eight herbicide treatments were applied postemergence to tropical signalgrass seedlings at the two-, four-, six-, and eight-leaf stages. Asulam and CGA 362622 provided ≥89% tropical signalgrass control at all application timings. Imazaquin controlled tropical signalgrass ≥98% when applied before the eight-leaf stage. However, in field trials with mature tropical signalgrass (>20 cm stolons), none of the 20 herbicide treatments applied postemergence provided acceptable control. Nomenclature: Asulam; benefin; CGA 362622, N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]-3-(2,2,2-trifluoroethoxy)-2-pyridinesulfonamide; 2,4-D; imazapic; imazaquin; oryzalin; blanket crabgrass, Digitaria serotina (Walt.) Michx. #3 DIGSO; India crabgrass, Digitaria longiflora (Retz.) Pers. # DIGLO; St. Augustinegrass, Stenotaphrum secondatum (Walt.) Kuntz; torpedograss, Panicum repens L. # PANRE; tropical signalgrass, Urochloa subquadripara (Trin.) R. D. Webster # BRASU. Additional index words: BRASU, DIGLO, DIGSO, PANRE. Abbreviation: WAA, weeks after application.

Star-of-Bethlehem (Ornithogalum umbellatum) Control with Postemergence Herbicides in Dormant Bermudagrass (Cynodon dactylon) Turf1

Field studies were conducted near Knoxville, TN, during late March and early April 2002 and 2003, respectively, for star-of-Bethlehem control in dormant bermudagrass turf that was established over 25 yr ago. Halosulfuron, imazaquin, metsulfuron, 2,4-D plus dicamba plus mecoprop, and triclopyr plus clopyralid controlled star-of-Bethlehem 35% at most 35 d after treatment (DAT). Bromoxynil alone or mixed with halosulfuron, imazaquin, or metsulfuron controlled star-of-Bethlehem at least 80% at 35 DAT. Imazaquin and imazaquin plus bromoxynil injured bermudagrass 51% 35 DAT. This injury was characterized by decreased bermudagrass postdormancy transition and was transient. Nomenclature: Bromoxynil; clopyralid; 2,4-D; dicamba; halosulfuron; imazaquin; mecoprop; metsulfuron; triclopyr; common bermudagrass, Cynodon dactylon (L.) Pers. #3 CYNDA; star-of-Bethlehem, Ornithogalum umbellatum L. # OTGUM. Additional index words: Glyphosate, golf course, postdormancy transition. Abbreviation: DAT, days after treatment.

Hybrid Kentucky Bluegrass Tolerance to Preemergence and Postemergence Herbicides

Field studies were conducted near Knoxville, TN, from 2003 to 2005 to evaluate the response of ‘Thermal Blue’, a new interspecific hybrid Kentucky bluegrass to commonly applied PRE and POST herbicides for weed management. Dithiopyr, oryzalin, oxadiazon, pendimethalin, prodiamine, quinclorac, and trifluralin applied at seeding injured hybrid bluegrass greater than 81% and reduced hybrid bluegrass cover greater than 57%. In a second study, established hybrid bluegrass was treated POST with acetolactate synthase–inhibiting herbicides including bispyribac-sodium, chlorosulfuron, foramsulfuron, halosulfuron, imazapic, imazaquin, metsulfuron, rimsulfuron, sulfosulfuron, and trifloxysulfuron at low and high rates (one and two times the suggested use rates in Kentucky bluegrass or other turfgrasses). By 5 wk after treatment (WAT), foramsulfuron at 88 g ai/ha and trifloxysulfuron at 35 g ai/ha injured hybrid bluegrass greater than 26% and reduced visually estimated quality and chlorophyll meter indices. However, hybrid bluegrass injury was no longer evident at 10 WAT. In a third study, established hybrid bluegrass was treated with clethodim, diclofop-methyl, fluazifop-p-butyl, and sethoxydim applied at low, medium, and high rates (0.5, 1, and 2 times the registered Kentucky bluegrass or other turfgrass use rates). Clethodim applied at 280 and 560 g ai/ha, fluazifop at 420 g ai/ha, and sethoxydim at 630 g ai/ha injured hybrid bluegrass 5 WAT. These treatments also reduced quality (to less than 5 on a scale of 1 to 9) and chlorophyll meter indices (24 to 37%) when compared to the untreated control. By 10 WAT, only clethodim at 560 g ai/ha caused injury (14%). By 10 WAT, hybrid bluegrass had recovered and injury was only observed in plots treated with clethodim at 560 g ai/ha. No differences in chlorophyll indices or quality were observed at 10 WAT for any POST graminicides. Nomenclature: Bispyribac-sodium, chlorosulfuron, clethodim, diclofop-methyl, dithiopyr, fluazifop-p-butyl, foramsulfuron, halosulfuron, imazapic, imazaquin, metsulfuron, oryzalin, oxadiazon, pendimethalin, prodiamine, quinclorac, rimsulfuron, sethoxydim, sulfosulfuron, trifloxysulfuron, trifluralin, Kentucky bluegrass, Poa arachnifera Torr. × P. pratensis L. ‘Thermal Blue’

Green Peanut Tolerance to Preemergence and Postemergence Herbicides

Field studies were conducted near Sparr, FL, in 2001 and 2002 to evaluate the response of ‘Valencia 102’ grown for the green peanut market (or boiling peanut) to preemergence (PRE) and postemergence (POST) applications of herbicides registered for dry peanut production (roasted market). Green peanut exhibited excellent tolerance to most PRE and POST treatments. There was minimal injury (8%) from flumioxazin applications when evaluated early season in both years, and peanut quickly recovered. Norflurazon caused chlorosis to peanut foliage (23%) in both years. Yield reduction was observed in 2001 for flumioxazin (15%), metolachlor (20%), and norflurazon (41%) compared with the untreated control. However, there were no yield reductions for any of the PRE treatments in 2002. Bentazon + paraquat early postemergence (EPOST) followed by (fb) 2,4-DB POST, bentazon + paraquat EPOST fb clethodim POST, and imazapic EPOST caused ≤5% injury and had no effect on yield in either year. Nomenclature: Bentazon; clethodim; 2,4-DB; flumioxazin; imazapic; metolachlor; norflurazon; paraquat; peanut, Arachis hypogaea L. ‘Valencia 102’. Additional index words: Herbicide injury, chlorimuron, diclosulam, dry peanut, ethalfluralin, fluazifop, green peanut, imazethapyr, pryridate, sethoxydim. Abbreviations: DAP, days after planting; EPOST, early postemergence; fb, followed by; POST, post-emergence; PRE, preemergence; WAE, weeks after emergence.

Characterization of Fluazifop-P-butyl Activity on Bristly Starbur (Acanthospermum hispidum)1

During routine use of fluazifop-P-butyl for grass control, county extension agents in Georgia observed control of bristly starbur in grower fields. Experiments to characterize the activity of fluazifop-P-butyl on bristly starbur were conducted under greenhouse conditions in Gainesville, FL, during 2001 and 2002. Fluazifop-P-butyl activity was characterized as a function of herbicide rate and time after application. Commercially available fluazifop-P-butyl was compared to technical fluazifop-P-butyl as a function of herbicide rate and bristly starbur height. Finally, injury to bristly starbur was evaluated when clethodim, diclofop, fluazifop-P-butyl, haloxyfop, quizalofop-p, and sethoxydim were applied at two growth stages. Fluazifop-P-butyl caused >90% injury to bristly starbur with all other post graminicides displaying <8% injury. Nonlinear regression revealed a sigmoidal response of bristly starbur injury to fluazifop-P-butyl. Estimates for 50 and 90% bristly starbur injury (I50 and I90) were 0.07 and 0.14 kg ai/ha, respectively. There was no difference in activity of technical and commercial fluazifop-P-butyl formulations. There was a differential response of bristly starbur to fluazifop-P-butyl over time as a function of plant height at the time of treatment. However, 14 days after treatment (DAT) all treatments displayed >89% injury. Bristly starbur response to fluazifop-P-butyl was similar to injury associated with contact-type herbicides. Nomenclature: Clethodim; diclofop; fluazifop-P-butyl, Fusilade DX; haloxyfop; quizalofop-p; sethoxydim; bristly starbur, Acanthospermum hispidum DC #3 ACNHI. Additional index words: ACCase, aryloxyphenoxy, cyclohexanedione, protoporhyrinogen oxidase, PROTOX, Arachis hypogaea L., Gossypium hirsutum L. Abbreviations: ACCase, acetyl-CoA carboxylase; POST, postemergence; WAE, weeks after emergence.