| Author Affiliation: | Gover: Project Associate, Penn State University, University Park, PA; Johnson: Project Associate, Penn State University, University Park, PA; Kuhns: Professor, Penn State University, University Park, PA |
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| Abstract/Contents: | Canada thistle (Cirsium arvense (L.) Scop.) is a common weed in roadside plantings of crownvetch (Coronilla varia L.) in Pennsylvania. Where infestations are severe, conversion to a grass mixture is a recommended option. As part of an ongoing research project funded by the PA Department of Transportation, a series of trials were established to evaluate several herbicides as tank mix partners for glyphosate to enhance the activity of the initial herbicide treatment against the Canada thistle-crownvetch complex without inhibiting grass establishment. Two trials were established to investigate the effect of herbicides applied at different intervals before seeding on the establishment of a fine fescue mixture. A trial seeded August 19, 1997, compared glyphosate at 3.4 kg/ha; clopryalid at 0.21 and 0.42 kg/ha; picloram at 0.56 and 1.1 kg/ha; chlorsulfron at 0.021 and 0.042 kg/ha; metsulfron methyl at 0.021 and 0.042 kg/ha; and imazapyr at 0.14 and 0.28 kg/ha. These treatments were applied 72, 36, 25, and 7 days before seeding (DBS). The experiment was seeded to a 55/35/10 percent mixture of hard fescue (Festuca brevipila Tracey), red fescue (Festuca rubra ssp. rubra L.) and annual ryegrass (Lolium multiflorum Lam.), respectively, seeded at 112 kg/ha. A second trial was seeded June 19, 1998, comparing glyphosate at 3.4 kg/ha alone and in combination with the same treatments as the 1997 trial, except for the deletion of the high rate of imazapyr, and the addition of triclopyr at 1.1 kg/ha and dicamba at 1.1 kg/ha. These treatments were applied 56, 28, 14, and 7 DBS. This trial was seeded to a 60/40 mix of hard fescue and creeping red fescue, respectively, at 112 kg/ha. The experimental design for both trials was a randomized complete block with a split-plot treatment arrangement, with application time as the whole plot. Both trials were conducted on an Opequon-Hagerstown complex (Lithic hapludalf) in a glyphosate-killed stand of Kentucky bluegrass (Poa pratensis L.). Prior to study initiation, the killed sod was shredded with a Lely Roterra to an approximate depth of 5 cm to expose the mineral soil. The seeding was done with a tractor-mounted slice seeder, dropping seed over slits approximately 1.2 cm deep on 7.6 cm centers. Both trials were irrigated as needed to keep the seedbed moist. For first season ratings of grass establishment, there was a significant interaction between application timing and herbicide treatment for both trials. There was no significant effect due to herbicide treatment for the earliest application dates in either trial. Establishment differences became evident in the treatments applied 36 DBS in the 1997 trial, and 28 DBS in the 1998 trial. In the 1997 trial, for percent total cover ratings taken 64 days after seeding, the 36 DBS glyphosate treated plots had 77 percent cover, while chlorsulfron at 0.026 and 0.052, and imazapyr at 0.28 kg/ha had signicifantly less at 55, 33, and 30 percent respectively. As the interval between treatment and seeding decreased to 7 days, imazapyr at 0.14 and metsulfron methyl at 0.021 and 0.042 kg/ha also significantly reduced ground cover compared to glyphosate alone. In 1998, for ratings of percent fine fescue cover taken 125 days after seeding, glyphosate plus picloram at 3.4 plus 0.56 kg/ha treatments had 93 and 94 percent fine fescue cover, for the 28 and 7 DBS treatments, respectively. Chlorsulfron at 0.052, metsulfron methyl at 0.042, and imazapyr at 0.14 kg/ha, applied 28 DBS, were rated significantly lower at 42, 48, and 55 percent, respectively. At 7 DBS, these three treatments provided 10, 42, and 30 percent cover, respectively. Percent fine fescue cover ratings in the 1997 trial, taken in October, 1998, ranged from 94 to 97 percent, indicating that full stands can develop despite inhibition during early establishment. However, considering that clopyralid, picloram, dicamba, or triclopyr did not inhibit establishment under any of the observed conditions, there is little justification to potentially reduce establishment during renovation by including chlorsulfron, metsulfron methyl, or imasapyr in the pre-plant application." |
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