Suppressing seedheads can help lower roadside maintenance costs and improve worker safety.
The job sounds simple: keep roadsides clear of tall vegetation. But each growing season, roadside managers know that more than bugs are hiding in the brush. Excess costs, increased liability and added safety risks accompany the workers when they mow, but allowing roadsides to overgrow can pose a danger to drivers.
Working to better balance vegetation control, program costs and worker safety, some states are considering integrated vegetation management (IVM) programs, which include mowing and herbicide applications. State departments of transportation are using herbicides to suppress the growth of plant seedheads, stunting vegetation height without negatively affecting turf appearance. Applied before seedhead development or after mowing, a seedhead suppression program uses a low rate of herbicide to reduce the growth rate of desirable roadside vegetation including bahiagrasses, tall fescue and bermudagrass.
“Seedhead suppression programs reduce plant height and decrease the need for repetitive mowings, with acceptable discoloration to the turf,” says Fred Yelverton, extension specialist and professor of crop science at North Carolina State University in Raleigh. “By managing the seedhead growth of both cool- and warm-season grasses, including tall fescue and bahiagrass, these types of programs can cut down on the number of times crews have to be out on the highway right-of-way.”
The Missouri Department of Transportation (MoDOT) has developed a Plant Growth Regulator (PGR) program to contain tall fescue along Route 66 and other state, where the grass is used to beautify and help control erosion. However, growing to 36 inches or higher in an average season, fescue can quickly disrupt natural habitat and obstruct sightlines for drivers.
Traditionally, Missouri's 10 roadside management districts relied on mowing to control fescue growth. But, with 250,000 acres to mow an average of three to four times a year at a cost of $40 to $45 per acre, the department's fescue-mowing expenses were growing nearly as fast as the vegetation.
About 15 years ago, MoDOT began exploring the use of a PGR program to reduce the need for mowing, cut labor costs and improve worker safety. “When we started our PGR program, we were trying to find a way to mow less but still get the same results,” says Rand Swanigan, roadside management specialist for MoDOT. “Herbicides are an important tool to help accomplish this goal.”
To develop the program, MoDOT tested several herbicides and found they reduced work hours dedicated to vegetation management. In some cases, areas that once required a minimum of three mowings or more to control fescue required only one under the PGR program. “The PGR tests demonstrated that we could stretch out our mowing cycles and put the labor force on the road surface, which is our priority,” Swanigan says.
According to Dan Sherbo, the Roadside Manager for MoDOT's South Central District Nine, which includes Route 66, those test results drove his district to adopt a PGR program in 2003. The district used it to treat more than 6,000 roadside acres — about a quarter of the total PGR acres the MoDOT managed that year.
“The PGR program reduced our total number of mowings and made the mowings we did easier because the grass was at a more manageable height,” Sherbo says. “This total reduction in labor hours dedicated to vegetation management, along with reduced equipment and material costs related to the PGR program, reduced our roadside costs by $300,000 from 2002 to 2003.”
Swanigan introduced the PGR program, and by 2003, MoDOT managed 25,000 acres under it, reducing the mowings on Missouri's PGR-treated roadsides from three or four times per year to only one or two per year. The reduction in mowings and transfer of labor to other priorities is the driving force behind the nearly $3 million MoDOT has saved since adopting the statewide PGR program. Fewer mowings also have helped decrease equipment and maintenance costs, delay the need to buy new mowing equipment and improve safety conditions for employees, who are not required to mow as often in roadside areas.
Georgia adds suppression
Georgia has spent several years studying the effects of combining mowing and selective herbicides into an IVM program to control bermudagrass. Ray Dorsey, agronomist manager for the Georgia Department of Transportation (GDOT), has led Georgia's efforts to suppress bermudagrass on nearly 30,000 miles of state highways. Over the last seven years, Dorsey and his colleagues have used a combination of selective herbicides and traditional mowing to save GDOT money, manpower and time.
Bermudagrass is a perennial, warm-season grass that blankets roadsides throughout Georgia. It permits drainage, keeping roadways clear of puddles and stays green throughout most of the spring and summer. However, if left uncontrolled, the rapidly growing bermudagrass can clog roadsides, preventrunoff and inhibit driver visibility.
When Dorsey joined Georgia's DOT in 1997, the state had relied on a traditional bermudagrass treatment program, which included mowing four to six times per year and applying herbicide six to eight times. Spraying season lasted from January to November, with mowings throughout spring and summer. Because bermudagrass and other roadside weeds were showing tolerance, Dorsey decided to examine the program's effectiveness. “It was time to look at the program and re-evaluate our options,” Dorsey says.
Working with Tim Murphy, weed science specialist at the University of Georgia in Athens, Dorsey tested herbicides to suppress grass seeds. Starting in southern Georgia and gradually moving north, the GDOT tested the seed suppression program in roadside areas for about one year, from 1998 to 1999. Dorsey and his team saw results quickly.
“For us, the herbicide treatment was basically a chemical substitute for mowing — and that's what we started calling it, a chemical mowing herbicide,” Dorsey says. As a result, GDOT reduced mowings to around two per year. By 2002, the entire state had converted to using herbicide for seedhead suppression and roadside weed control.
“Our mowing cost today is about $37 per acre, which is almost a 50 percent savings from what we were paying before we started using herbicide in-between mowing treatments,” Dorsey says. He also says his herbicide costs have been reduced to around $10 per acre.
GDOT's lower costs resulted from decreasing the number of mowings per year from six to two and reducing overall herbicide used per acre per year. “Today, we are applying less herbicide per acre, and we're also applying it much less often than before,” Dorsey says.
Improving safety for each Georgia state employee is a key goal for Dorsey, and fewer employees on fewer mowers has created a safer workforce. Today's GDOT herbicide applicators use 50 boomless trucks each with a 1,000- to 1,500-gallon capacity, which Dorsey says are much less dangerous to use on roadsides than mowers. “Compared to a mower, we can keep employees safer and out of traffic when they are driving a truck,” he says.
GDOT also is saving time on its roadside vegetation-control efforts. Its previous herbicide program required four or five applications yearly versus its current treatment program, which requires only one to two chemical applications every year.
Pennsylvania State University has developed a research program devoted to investigating right-of-way management techniques, through which researchers work closely with the Pennsylvania Department of Transportation Bureau of Maintenance to identify the best IVM programs. Art Gover, research support associate at Penn State says most DOTs should create an IVM program because they face “an expanding palette of species” that are invading roadsides and producing increased public pressure to control them. Unfortunately, the dollars and personnel are not expanding to keep pace.
“The challenge is if the existing program is ‘fighting fires,’” Gover says. “It's hard to devote new funds to a new program, especially in areas that don't seem to be that problematic. Convincing stakeholders to take a more preventive, or maintenance, approach can be very difficult when the program is still in a control phase.”
Gover believes the applicator is the key to successful operation of an IVM program. When applicators understand the specific objectives of an IVM program, the intricacies of their equipment and the capabilities of the herbicide products at their disposal, they can make informed, sound decisions out in the field.
“IVM allows roadside managers to take a structured approach to common sense management,” Gover says. “It's like a business with a sound strategic plan [and] helps vegetation managers manage more effectively and preventively.”
Todd Horton is market development specialist for Research Triangle Park, N.C.-based BASF.