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1 July 2010 Plant Community Response to Integrated Management of Meadow Hawkweed (Hieracium caespitosum) in the Pacific Northwest
John M. Wallace, Timothy S. Prather, Linda M. Wilson
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Meadow hawkweed is an invasive, perennial forb of upland forest openings, mountain meadows, permanent pastures, and abandoned farmlands in the Pacific Northwest. The objective of this study was to measure the plant community response, following meadow hawkweed control using selective herbicides and a single application of N–P–K fertilizer, across three levels of meadow hawkweed infestation in cleared forestlands that had been converted to pasture in northern Idaho. Clopyralid was applied to meadow hawkweed rosettes at a rate of 0.59l kg ae ha−1 (0.528 lb ac−1), and fertilizer (23–5–5, 1% Fe, 14% S) was broadcast following herbicide applications at two rates, 44 and 88 kg N ha−1. Foliar cover of meadow hawkweed, Idaho fescue, and other perennial grasses was measured in microplots at three levels of initial meadow hawkweed cover; < 25%, 40 to 60%, and > 75%. Clopyralid treatments resulted in excellent meadow hawkweed control 3 mo after treatment (MAT). Clopyralid alone appeared to shift the competitive balance in favor of perennial grasses, which increased 7, 44, and 65% above pretreatment levels in LOW, MED, and HIGH hawkweed cover plots, respectively, across fertilizer treatments. Meadow hawkweed cover remained < 5% in clopyralid plots at 52 MAT. Fertilizer effects were confined to interactions between Idaho fescue and other perennial grasses.

Nomenclature: clopyralid; Idaho fescue, Festuca idahoensis Elmer; meadow hawkweed, Hieracium caespitosum Dumort

John M. Wallace, Timothy S. Prather, and Linda M. Wilson "Plant Community Response to Integrated Management of Meadow Hawkweed (Hieracium caespitosum) in the Pacific Northwest," Invasive Plant Science and Management 3(3), 268-275, (1 July 2010).
Received: 20 February 2009; Accepted: 1 April 2010; Published: 1 July 2010
integrated weed management
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