Picloram, fertilizer, and defoliation interactions on spotted knapweed reinvasion
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Authors: J. S. Jacobs, R. L. Sheley, and J. R. Carter
Date: 2000
Journal: Journal of Range Management
Volume: 53
Number: 3
Pages: 309-314
Summary of Methods: Rate of spotted knapweed reinvasion in relation to Picloram, fertilizer and defoliation treatments was examined in this clipping study west of Bozeman, Montana for three years. Sixteen chemical treatments (4 picolram rates, and 4 fertilizer rates) were applied to plots; within each plot one of six defoliation treatments (no defoliation, spring, summer, fall, alternating fall/spring, and spring-summer-and fall) was applied to subplots. Treatments were replicated across two sites (Idaho fescue and bluebunch wheatgrass). All grass plants within the subplot were hand-clipped to remove 60% of present standing crop present at each clipping. In August of 1997, juvenile and total spotted knapweed plants were counted and percent cover for spotted knapweed, all grass species, peak standing crop was clipped, and litter and bare ground was estimated prior to peak standing crop harvets.
Article Summary / Main Points:
• All rates of picloram decreased spotted knapweed density, cover and biomass and increased grass yield four years after treatment.
• Sites treated with fertilizer (N and P) tended to have higher spotted knapweed density and biomass.
• Fertilizer (N and P) plus defoliation in all three seasons increased spotted knapweed reinvasion into the Kentucky bluegrass dominated site over the site dominated by timothy and smooth brome.
• Fall only defoliation and no defoliation deterred spotted knapweed re-invasion better than the other use seasons.
• Reinvasion of spotted knapweed is dependent on grass species present at the site.Vegetation Types: Mountain Shrublands
MLRA Ecoregions: 44B Central Rocky Mountain Valleys
Agrovoc Control Words: Weeds Grazing Herbicides
Article Review Type: Refereed
Article Type: Experimental Research
Keywords: centaurea maculosa, integrated weed management, grass defoliation, grazing management, defoliation frequency, kentucky bluegrass, poa pratensis l., timothy, phleum pratense l., smooth brome, bromus inermis, spotted knapweed, targeted grazing
Annotation: This study is highly relevant as there are few studies that tested the rate of reinvasion by weed species when sites are controlled with chemicals. The presence of an understory of healthy grazing resistant species, reasonable grazing practices will not accelerate reinvasion of spotted knapweed. Though the presence of weaker grasses dominate the understory it is critical to avoid improper grazing practices to prevent the reinvasion of spotted knapweed.
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