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Variable impacts of imazapic rate on downy brome (Bromus tectorum) and seeded species in two rangeland communities

Author(s): Christo Morris, Thomas A. Monaco, Craig W. Rigby
Year Published: 2009

The herbicide imazapic is registered for use on rangelands and provides effective short-term control of certain invasive annual grasses. However, details about optimal application rates for downy brome and susceptibility of simultaneously seeded species are lacking. Thus, we investigated downy brome and seeded species responses to variable rates of imazapic (0, 35, 70, 105, and 140 g ai/ha) in two plant communities (salt desert shrub and Wyoming big sagebrush). In autumn 2003, plots were treated with imazapic and seeded with one of five perennial plant materials (Siberian wheatgrass, prostrate kochia, and Russian wildrye. Downy brome cover and seeded species establishment were evaluated in spring 2004 and 2006. Downy brome cover in 2004 decreased with increasing imazapic rate at both sites, although more so at the Wyoming big sagebrush site. In 2006, no difference in downy brome cover existed among herbicide rates at the Wyoming big sagebrush site. At the salt desert shrub site, the high rate of imazapic reduced downy brome cover by about 25% compared to untreated plots. 'Vavilov' Siberian wheatgrass was the only seeded species with lower downy brome cover in 2006 than 2004. Seeded species establishment increased with imazapic rate in the salt desert shrub community, but in the Wyoming big sagebrush community it peaked at intermediate rates and declined at higher rates. Variation in downy brome control and seeded species establishment might have been associated with differences in precipitation, soil organic matter, and disturbance history between sites. Overall, imazapic was useful for helping establish desirable perennial species, but unless downy brome is reduced below a critical threshold, favorable precipitation can return sites to pretreatment levels within two years.

Citation: Morris, Christo, Monaco, Thomas A.; Rigby, Craig W. 2009. Variable impacts of imazapic rate on downy brome (Bromus tectorum) and seeded species in two rangeland communities. Invasive Plant Science and Management. 2: 110-119.
Topic(s): Fire Ecology, Invasive Species, Management Approaches, Recovery after fire, Fire Effects, Ecological - Second Order
Ecosystem(s): Sagebrush steppe
Document Type: Book or Chapter or Journal Article
NRFSN number: 8332
FRAMES RCS number: 12476
Record updated: May 24, 2018