By: Julianne Mason, Forest Preserve District of Will County

Over the past decade, we’ve consistently found basal bark herbicide treatment to be the most efficient and effective way to control invasive shrubs. In fact, we now use basal bark treatments almost exclusively across thousands of acres of prairies, wetlands, and woodlands in northeastern Illinois, in place of traditional cut stump methods.

For anyone unfamiliar with the technique, basal bark treatment is an herbicide-only application. We typically use a 15% solution of Garlon 4 (or a comparable triclopyr ester product) mixed in a commercially formulated bark oil. The herbicide is sprayed onto the lower 3–12 inches of the stem, depending on shrub size. Smaller stems only need a narrow 3-inch band, while larger shrubs require a wider treated area. We apply the mixture with backpack sprayers set to low pressure and large droplet sizes to minimize overspray. It’s important to make a 360 degree application around the entire circumference of the stem.  It’s important to use an official bark oil (not diesel or other weird oils). 

When done properly, basal bark treatment has proven effective for us year-round, as long as there is no snow cover (winter consideration) and as long as temperatures are below about 85°F to reduce the risk of herbicide volatilization and vapor drift (summer consideration).

Over the years, we’ve had many discussions comparing basal bark and cut stump treatments. Cut stump methods certainly satisfy our human desire for instant gratification — there’s something emotionally satisfying about cutting down a shrub and seeing it gone immediately. But once we get past that emotional reaction, I think the evidence strongly favors basal bark treatments for many situations. They are often faster, less disruptive, and, in our experience, more consistently effective.

Last spring, we stumbled into an unexpected discovery because of a scheduling mistake. An ecological contractor was scheduled to conduct basal bark treatments in a prairie and wetland near Braidwood, IL. However, we forgot to tell them that we had just conducted a prescribed burn there the previous day.

The crew arrived, saw that the entire site had been burned, and decided to proceed anyway. They essentially sprayed the bases of shrubs that had already been top-killed by the fire. When I heard what happened, I was upset that they had wasted time and herbicide treating dead stems that would no longer be able to absorb or translocate the herbicide.

I was completely wrong.

All of the invasive shrubs died following the treatment. Without herbicide, those shrubs would have vigorously resprouted after the fire. In our region, dormant-season fire alone generally does not kill established invasive shrubs. Yet even large, 3-inch diameter bush honeysuckles, autumn olive, callery pear and buckthorns were effectively controlled after the post-burn herbicide application.

Just as importantly, the treatment proved remarkably efficient. The crew raved about how easy it was to move through the burned prairie. The blackened, top-killed shrubs stood out visually and were incredibly easy to locate and treat.

Encouraged by those results, our crew spent much of the past winter and spring experimenting further with post-burn basal bark applications of Garlon 4 in recently burned prairies. I’m excited to report that the original results were not a fluke.

We’ve successfully treated sites anywhere from a few days after burning to as much as three months post-burn in areas burned last fall. Treatments in recently burned prairies have been especially effective because the invasive shrubs stand out so clearly against the burned landscape. In woodlands, where native and invasive shrubs are more intermixed, it can be more difficult to quickly distinguish which blackened stems should be treated. But in prairies, especially where the shrubs are mostly invasive and visually distinct from native ones, post-burn treatments have been outstanding.

The combination of visibility, ease of movement, and effectiveness has made this one of the most promising invasive shrub control techniques we’ve used in years.  So easy, so effective, highly recommended!

p.s. We may have finally defeated common buckthorn on the ridges of several of our dolomite prairie preserves. For more than 30 years, we intermittently cut the invasive shrubs, treated stumps, sprayed resprouts, and repeatedly top-killed them with prescribed fire. After decades of effort, a single post-burn basal bark treatment appears to have accomplished what all those previous efforts did not.

p.s.s. It feels like we’ve stopped spinning our wheels, and can actually make progress addressing the scale of invasive shrub control that’s needed. It’s spring, and hope feels great!