Selective herbicides proven effective for fuel break maintenance

There are many options for fuel break maintenance: herbicides, mowing, hand-trimming, grazing, and more.
Which methods are most cost-effective, and which provide the highest level of control?
A new study from the University of California Cooperative Extension looks at the options.

As both the risk and severity of wildfires have continued to increase across the United States, vegetation managers, and the departments and organizations they serve, have a key role to play in helping reduce the impact of fires that do occur. A key component of risk mitigation? Fuel breaks.

“A fuel break is simply a reduction in the level of fuel in a given area,” said Jerome Otto, market development specialist with Corteva Agriscience. “Literally, we’re just breaking up that contiguous fuel load that’s formed by dense underbrush.”

By removing the most flammable plant materials, vegetation managers create a two-fold benefit. First, a strategically placed fuel break can give firefighters a chance to stop a fire before it jumps to an adjoining area. Second, a fuel break can also provide an ingress or egress route for firefighters, first responders and members of the public who may be trapped.

Two types of fuel breaks

Fuel breaks may come in all shapes and sizes, but they can generally be categorized in one of two ways: shaded or non-shaded. A non-shaded fuel break likely has most or all vegetation removed and is created to stop a fire. A shaded fuel break modifies the behavior of a fire by keeping flames close to the ground and reducing the speed of the fire’s spread.

“A shaded fuel break still has some trees,” Otto said. “But the stem density of the trees is greatly reduced, and the brush is removed so that the ladder fuels – the fuels that help a fire go from the ground to the top or crown of a tree – are greatly reduced.”

And while placement and design of a fuel break will be determined by a number of factors, one aspect of fuel break establishment holds true, regardless of design or location: maintenance.

“It’s not enough to establish a break and walk away,” Otto said. “That fuel will regrow, and, often, the first species to come back are highly flammable grasses, so we need to maintain them.”

Fuel break maintenance: A critical step

After completing a thorough site evaluation, vegetation managers face a range of choices for controlling undesirable vegetation. Grazing, mowing and hand-pruning are all options, though each has definite downsides. Grazing may work for smaller areas, and mowing may work for areas that are relatively flat. But both are expensive and can be severely disruptive to wildlife or pollinator species you may want to protect.

In addition, mowing carries a much larger carbon footprint and can generate sparks that may start the very fire a vegetation manager wants to prevent. So,what’s the answer?

“A highly effective and cost-effective treatment for maintaining these fuel breaks is to use selective herbicides,” Otto said. “That is, herbicides that take out the flammable species that we don’t want but leave behind species that are beneficial to wildlife and pollinators.”

The other “pro” to selective herbicide use? It’s typically the least expensive of the vegetation management options.

Study confirms herbicides provide cost-effective fuel break maintenance

Dr. Scott Oneto, with the University of California Cooperative Extension, recently completed a study examining the per-acre costs of various chemical and mechanical vegetation management programs on fuel breaks. For his study, Oneto compared the percentage of control and the costs associated with grazing, flaming and hand-trimming to those of 20 different chemical treatments.

After comparing the various programs, the study concluded that the most effective maintenance programs used spot treatment with selective herbicides, and that these treatments not only performed better than other methods, but they were also consistently less expensive than grazing, hand-trimming or flaming.

“Selective herbicide treatments tend to be the most effective and the least costly on a per-acre or per-mile basis,” Otto said. “In addition, we have over six decades of research from projects like State Game Lands 33 showing how the use of selective herbicides not only can keep trees and brush down, but they also benefit pollinators, ground dwelling insects and wildlife such as deer. Plus, the research shows that these advantages have been very consistent over the years.”

Ultimately, the decision of how to maintain a given fuel break will come down to its location and type, and the desirable and undesirable plant species. Regardless, vegetation managers in fire-prone regions should be ready to employ every available measure to mitigate the risk and spread of fire.

“Wildfires have continued to increase in both frequency and severity across the western United States,” Otto said. “So, we continue to look at new ways to manage the fuel load and reduce the impact of these fires. Properly managed and maintained, fuel breaks provide a critical strategic tool that can help firefighters slow or stop the spread of fire and protect the people and structures in the fire’s path.”

Read Oneto’s study on cost-per-acre on chemical and mechanical vegetation management programs on fuel breaks here.

Also be sure to visit the Corteva Vegetation Management fire prevention and mitigation page.

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