The tolerance of velvet bentgrass (Agrostis canina L.) to the herbicide fenoxaprop is not known. In greenhouse experiments velvet bentgrass cultivars SR7200 and Vesper had a much greater degree of tolerance to fenoxaprop at rates ranging from 0.01 to 0.30 kg·ha-1 relative to L-93 creeping bentgrass (Agrostis stolonifera L.). SR7200 and Vesper were tolerant to fenoxaprop at 0.15 kg·ha-1 or lower and growth reductions did not exceed 10% at the highest fenoxaprop rate of 0.30 kg·ha-1. In contrast, growth reduction of L-93 creeping bentgrass was evident at the lowest application of fenoxaprop at 0.01 kg·ha-1 and increased as fenoxaprop rates increased, reaching as high 58% at 0.30 kg·ha-1. Field experiments were conducted in 2002 and 2003 to compare the tolerance of established SR7200 velvet bentgrass and Penn A-4 creeping bentgrass maintained at 3.2 mm to three sequential applications at 21 day intervals of fenoxaprop at 0.02, 0.04, and 0.07 kg·ha-1. Turf quality of SR7200 was equal to the untreated following all fenoxaprop applications except the third sequential application at 0.07 kg·ha-1. Penn A-4 turf quality was consistently reduced compared to the untreated following fenoxaprop applications of 0.04 and 0.07 kg·ha-1. Turf density of SR7200 was not affected by three sequential applications of fenoxaprop at 0.02 and 0.04 kg·ha-1 but was reduced by 8% at 0.07 kg·ha-1. Penn A-4 turf density was reduced by 10 and 33% following three sequential applications of fenoxaprop at 0.04 and 0.07 kg·ha-1, respectively. Results from these studies showed that the velvet bentgrass cultivars were more tolerant to fenoxaprop, compared to the creeping bentgrass cultivars evaluated. Chemical names used: (+)-ethyl2-[4-[(6-chloro-2-benzoxazolyl)oxy]p henoxy] propanoate (fenoxaprop). 3,5-pyridinedicarbothioic acid, 2-(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-S,S-dimethylester (dithiopyr).
Gerald M. Henry and Stephen E. Hart
Darren W. Lycan and Stephen E. Hart
Previous research has demonstrated that bispyribac-sodium can selectively control established annual bluegrass (Poa annua L.) in creeping bentgrass (Agrostis stolonifera L.). Annual bluegrass is also a problematic weed in other cool-season turfgrass species. However, the relative tolerance of other cool-season turfgrass species to bispyribac is not known. Field experiments were conducted at Adelphia, N.J., in 2002 and 2003 to gain understanding of the phytotoxic effects that bispyribac may have on kentucky bluegrass (Poa pratensis L.), perennial ryegrass (Lolium perenne L.), tall fescue (Festuca arundinacea (L.) Schreb.), and chewings fine fescue (Festuca rubra L. subsp. commutata Gaud.). Single applications of bispyribac at 37 to 296 g·ha–1 were applied to mature stands of each species on 11 June, 2002 and 10 June, 2003. Visual injury was evaluated and clippings were collected 35 and 70 days after treatment (DAT). Visual injury at 35 DAT increased as bispyribac rate increased. Kentucky bluegrass was least tolerant to bispyribac with up to 28% injury when applied at 296 g·ha–1. Injury on other species did not exceed 20%. Initial injury on perennial ryegrass, tall fescue, and chewings fine fescue was primarily in the form of chlorosis, while kentucky bluegrass exhibited more severe stunting and thinning symptoms. Bispyribac at rates from 74 to 296 g·ha–1 reduced kentucky bluegrass clipping weights by 19% to 35%, respectively, as compared to the untreated control at 35 DAT in 2002. Initial visual injury on perennial ryegrass, tall fescue, and chewings fine fescue dissipated to ≤5% by 70 DAT. However, recovery of kentucky bluegrass was less complete. These studies suggest that bispyribac-sodium has potential to severely injure kentucky bluegrass. Injury on perennial ryegrass, tall fescue, and chewings fine fescue appears to be less severe and persistent; therefore, bispyribac can be used for weed control in these species. Chemical names used: 2,6-bis[(4,6-dimethoxy-2-pyrimidinyl)oxy]benzoic acid (bispyribac-sodium).
Gerald M. Henry, Stephen E. Hart and James A. Murphy
Field trials were conducted in 2000 and 2001 to determine the potential of converting pure stands of annual bluegrass [Poa annua L. spp. reptans (Hauskins) Timm.], maintained at a 3.2-mm height, to bentgrass (Agrostis spp.). Parameters evaluated included three overseeding dates and four cultivars from two bentgrass species. Overseeding dates were 1 July, 18 Aug., and 18 Sept. 2000 and 27 June, 17 Aug., and 17 Sept. 2001. Three creeping bentgrass (A. stolonifera L.) cultivars (`Penncross', `L-93', and `Penn A-4') and one velvet bentgrass (A. canina L.) cultivar (`SR7200') were evaluated. Initial bentgrass establishment was evident across all seeding dates and cultivars in October of the year of overseeding. However, the 1 July 2000 and 27 June 2001 overseeding dates had the highest levels of bentgrass coverage 12 months after overseeding across all cultivars except `Penncross'. Coverage of `Penn A-4' and `L-93' increased to 72% in the 1 July 2000 overseeding date, 24 months after the initial overseeding. When overseeded in early summer, velvet bentgrass `SR7200' showed the greatest potential for establishment with annual bluegrass. `SR7200' and creeping bentgrass cultivars `Penn A-4' and `L-93' exhibited the greatest potential for long-term competitiveness with annual bluegrass, while `Penncross' exhibited the lowest potential.
Robert R. Shortell, Stephen E. Hart and Stacy A. Bonos
Annual bluegrass (Poa annua L.) is a problematic weed in Kentucky bluegrass (Poa pratensis L.). Bispyribac-sodium herbicide can effectively control established annual bluegrass in other cool-season turfgrasses, but unacceptable injury to Kentucky bluegrass has been reported. However, only a few Kentucky bluegrass cultivars have been evaluated. The objective of this study was to determine the extent of intraspecific variability among Kentucky bluegrass cultivars and selections to sequential applications of bispyribac-sodium herbicide. Field experiments were conducted in 2004 and 2005 in New Jersey to determine the response of 55 Kentucky bluegrass cultivars and selections to bispyribac-sodium. The herbicide was applied at 188 g·ha−1 followed 3 weeks later by a second application of 281 g·ha−1. Kentucky bluegrass injury ranged from 8% to 93% 8 weeks after initial treatment (WAIT). ‘Blackstone’, ‘Serene’, and A98-962 were the most tolerant to bispyribac-sodium, exhibiting less than 20% injury 8 WAIT. Conversely, ‘Washington’, 95AN-10, and ‘Avalanche’ were the most susceptible with up to 93% injury 8 WAIT. The range in tolerance to bispyribac-sodium within Kentucky bluegrass indicates the potential for the identification and development of cultivars with improved tolerance to bispyribac-sodium herbicide.
Patrick E. McCullough, Stephen E. Hart, Shawn Askew, Peter H. Dernoeden, Zachary Reicher and Dan Weisenberger
With the potential introduction of glyphosate-resistant kentucky bluegrass (GRKB) (Poa pratensis L.), postemergence herbicides must be identified for renovation from glyphosate-resistant stands or control escaped GRKB. Field experiments were conducted in Indiana, Maryland, New Jersey, and Virginia from July to September 2004 to investigate efficacy of postemergence herbicides for kentucky bluegrass control. Herbicides tested included clethodim at 0.28 kg·ha–1 (a.i.), fluazifop-p at 0.43 kg·ha–1 (a.i.), formasulfuron at 0.03 kg·ha–1 (a.i.), glufosinate at 1.12 kg·ha–1 (a.i.), glyphosate at 1.68 kg·ha–1 (a.i.), rimsulfuron at 0.03 kg·ha–1 (a.i.), sethoxydim at 0.53 kg·ha–1 (a.i.), and trifloxysulfuron at 0.03 kg·ha–1 (a.i.). One and two applications of each herbicide were applied to separate plots with the sequential applied 4 weeks after initial treatments (WAIT). Single applications of glyphosate completely controlled kentucky bluegrass 4 WAIT in Maryland, New Jersey, and Virginia. Glufosinate completely controlled kentucky bluegrass with one application in Maryland and New Jersey but single and sequential applications provided only 80% to 88% control in Indiana and Virginia. Foramsulfuron and rimsulfuron required sequential applications for complete kentucky bluegrass control 8 WAIT in New Jersey and Maryland but <82% control was obtained in Indiana and Virginia. Trifloxysulfuron controlled kentucky bluegrass 95% to 100% with single applications in Maryland, New Jersey, and Virginia. Single applications of clethodim, fluazifop, and sethoxydim provided minimal stand reductions but sequential applications controlled kentucky bluegrass 65% to 100%. Results suggest glufosinate and trifloxysulfuron have the greatest potential for controlling GRKB while other herbicides provided erratic control and require sequential applications.