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The timing of herbicide application following wildfire can strongly influence its effectiveness. USGS researchers evaluated the effect of the commonly used herbicide imazapic on targeted exotic annual grasses and non-target plants, applied the first winter or second fall after the 2015 Soda wildfire. 

They measured responses of species cover, diversity, and occurrence frequency of shrubs and forbs seeded prior to herbicide application. Cover of exotic annual grass, but not deep-rooted perennial bunchgrass, was less where imazapic had been applied. Imazapic effects did not vary with landscape factors studied such as elevation, annual precipitation, species richness, and other factors. Overall results showed that imazapic reduced exotic annual grasses when applied at various times during the first post-fire year, but had more effects on non-target plant species when applied in the first winter post-fire. A treatment sequence that staggers herbicide and seeding of desirable shrubs and forbs may be a useful approach towards integrated weed management.


Applestein, C.V., Germino, M.J., Fisk, M.R., 2018, Vegetative Community Response to Landscape Scale Post-fire Herbicide (Imazapic) Application: Invasive Plant Science and Management, p. online,

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