The period after a wildfire can offer a great window of opportunity for treating invasive plants. But scientists from the U.S. Geological Survey say timing matters.

After the 2015 Soda Wildfire on the Idaho-Oregon border, they conducted a study to compare landscape-scale applications of the herbicide imazapic made during two periods. The first applications were made in the winter, just one to two months after reseeding native plants. The second applications were timed for the following fall – nine to ten months after reseeding.

After measuring exotic and native species cover, diversity, and the occurrence of seeded shrubs and forbs, researchers found that imazapic reduced targeted exotic annual grasses regardless of when it was applied. The herbicide had a greater, negative impact on the reestablishment of native plant species, though, when applied soon after seeding.

The USGS study offers clear guidance for land managers. For optimal results, adopt a treatment sequence that staggers herbicide applications and the seeding of desirable shrubs and forbs.

Want to know more? See the article “Vegetative Community Response to Landscape Scale Post-fire Herbicide (Imazapic) Application” found in Volume 11, Issue 3 of the journal Invasive Plant Science and Management.

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