Auburn scientist helps ALDOT rethink roadside management

Highway safety is more than guardrails and speed limits. It’s also managing tens of thousands of acres of roadside vegetation to maintain clear sightlines, prevent erosion and provide safe areas for motorists and highway workers to stop.

A four-year research project at Auburn University is helping the Alabama Department of Transportation to manage its nearly 30,000 lane-miles of public roadside in more efficient, cost-effective ways by incorporating herbicide as part of an integrated weed management practice.

“It’s about safety first and foremost,” said David Russell, associate Extension professor of weed science. “Clear views, stable shoulders, and consistent vegetation are critical for drivers and maintenance crews.”

ALDOT is responsible for an estimated 243,000 acres of roadside ­— more than 10 times Alabama’s largest state park. Alabama provides important east-west and north-south corridors for Gulf Coast, Midwest and Southeast traffic. It maintains 1,200 miles of interstate roadside alone — the equivalent of a 200-foot-wide strip of grassland stretching from Boulder to Birmingham.

The traditional means of weed control is mowing. However, mowing is an expensive, one-size-fits-all approach. By some estimates, mowing costs $50 per acre several times each year. Mowing also exposes road workers to risk by placing them near traffic, and it often is simply ineffective against invasive grasses that regrow quicker than native species.

“Our goal was to create practical, research-based recommendations that ALDOT managers can use immediately across Alabama’s highway system,” said Russell.

The Auburn-led research sought to determine if targeted herbicide programs, applied at specific times, could outperform traditional methods to provide longer-lasting control, reduce the need for repeated mowing and improve roadside conditions.

Russell conducted field trials at multiple locations alongside Alabama’s highways (i.e., those mysterious “DO NOT MOW” signs along the interstate). The study targeted particularly problematic species in common management scenarios. Russell tested herbicide combinations, rates, timing and environmental conditions to identity treatments that delivered consistent control.

Russell discovered that controlling weeds is as much about the right time as it is the right combination of herbicides. Species such as silver beardgrass and vaseygrass, which have been notoriously difficult to manage, can be controlled for up to two months with the right combination of herbicides, if applied in late summer.

In designated “bareground areas” where vegetation must be removed completely to allow drainage to make roads safely passable, several herbicides were found to render 80% of the ground free of vegetation for up to 132 days.

Fire, which is often touted as a “natural” management tool, was found to actually cause the spread of the invasive species foxtail by stimulating its dormant seeds to germinate in the absence of a thick, healthy forage stand. The invasive often regrows faster than desirable grasses, choking them out after a fire clears an area.

Russell’s strategic approach also led to better habitat for pollinators like butterflies. Through field-applied research trials, their team proved that some our native milkweeds were tolerant to many commonly-used herbicides along highway rights-of-way. When not mowed repeatedly, native wildflowers like Rudbeckia were also able to emerge. In addition to protecting against erosion and preventing invasive species from getting a foothold, the flowers are also just nice for motorists to see along the roadside.

“This work shows that vegetation management doesn’t have to be a one-size-fits-all approach,” Russell said. “When we understand how different species behave and how treatments interact with the environment, we can manage roadsides in ways that are safer, more economical and more environmentally responsible.”

While the primary goal of Russell’s study was to improve weed control, the effects are much greater. By reducing the frequency of mowing and re-treatment of herbicides, his strategies have the potential to lower long-term maintenance costs, decrease fuel use and reduce the amount of time highway workers are exposed to dangerous traffic.

In addition to academic papers and technical reports, Russell has created demonstration plots and given many presentations to ALDOT managers through his Extension role. These efforts ensure results move beyond research into real-world application.

“Partnerships like this are at the heart of Auburn’s Land Grant mission,” Russell said. “When university research is able to inform how the state operates and serves its citizens, everyone benefits.”