| Abstract/Contents: | "As part of an ongoing research project funded by the Pennsylvania Department of Transportation, a study was initiated to compare three operational sequences to convert stands of crownvetch (Cornilla varia L.) infested with Canada thistle (Cirsium arvense (L.) Scop.) to a perennial, cool-season grass mixture. The operations in each sequence were a primary herbicide treatment to provide to initial control of the thistle/crownvetch stand, a secondary herbicide treatment to control remnant undesirable vegetation, and seeding of a 55/35/10 percent, by weight, mixture of hard fescue (Festuca brevipila Tracey), creeping red fescue (Festuca rubra ssp. rubra L.), and annual ryegrass (Lolium multiflorum Lam.), respectively, at 112 kg/ha. The sequences compared were SEQ1 - concurrent primary treatment and seeding in spring, secondary treatment late summer; SEQ2 - primary treatment spring, concurrent secondary treatment and seeding late summer; and SEQ3 - primary treatment late summer, seeding late summer, and secondary treatment the following spring. The study site was a 12 year-old stand of thistle-infested crownvetch and flatpea (Lathyris sylvestris L.) on a north-facing earthen berm, approximately 45 percent slope, at the interchage of SR 78 and SR 412, in Hellertown, PA[.] Individual plots were 9 by 15 m, arranged in a randomized complete block with three replications. The herbicide treatment used for all primary applications as well as the secondary application for SEQ2 was glyphosate plus clopyralid at 3.4 plus 0.21 kg ae/ha. The secondary treatment for SEQ1 and SEQ3 was dicamba plus clopyralid at 1.1 plus 0.21 kg ae/ha. All herbicide treatments included an organosilicone-based surfactant at 0.1 percent v/v. Herbicide applications were made using a lever-actuated, piston pumps backpack sprayer, equipped with a single spray tip. Spray tip selection varied with target conditions and applicator preference, and included Spraying Systems OC-04 off-center flat fan, 4004 flat fan, or #5500 ConeJet with X-6 tip. Pre-weighed lots of seed were distributed by hand for all seedings. SEQ1 received primary treatment and was seeded April 30, 1998. Canada thistle was up to 20 cm tall, and crownvetch was elongated up to 25 cm. When he[the] secondary treatment was applied August 31, 1998, average cover from total vegetation and fine fescue was 91 and 45 percent, respectively. SEQ2 received primary treatment May 28, secondary treatment August 31, and was seeded September 13, 1998. At primary treatment, the Canada thistle and crownvetch canopy was 75 to 90 cm tall. Average vegetative cover at the secondary treatment was 25 percent. The primary treatment was applied to to SEQ3 August 31, 1998. Average vegetative cover was 95 percent, 78 percent from crownvetch. Spring growth of Canada thistle had senesced, and late season resprouts provided 2 percent cover. Seeding and secondary treatment were done Spetember 13, 1998, and June 10, 1999, respectively. Fine fescue cover for SEQ1, SEQ2, and SEQ3 on June 10, 1999 was 68, 40, and 20 percent, respecitvely, and Canada thistle cover was 12, 2, and 6 percent, respectively. The difference in fine fescue establishment between SEQ2 and SEQ3, which were seeded the same day, appeared to be due to the repsective amounts of vegetative residue. The amount of residue in SEQ2 acted more as mulch, while recently-treated, full-canopy residue in SEQ3 appeared to be inhibitory. All plots were treated with triclopyr plus a pre-mix of 2,4-D, 2,4-DP, and dicamba at 0.84 plus 0.56, 0.56, and 0.14 kh/ha, respectively, on May 11, 2000. Fine fescue cover for all three treatments ranged from 94 to 96 percent on August 7, 2000, and Canada thistle was detected in only one plot. Establishment differences 13 months after trial initiation were temporary, and all three rehabilitation sequences effectively replaced Canada thistle infested crownvetch with a fine fescue mixture." |
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