Kevin Clemmer and Derek Smith's neon orange safety vests aren't the only specks of color along North Carolina's highways. A vibrant sea of wildflowers also catches the eyes of drivers whizzing by.
Clemmer and Smith work for North Carolina DOT's (NCDOT) Roadside Environmental Unit, which protects and controls the hundreds of species of plants and flowers lining North Carolina's roadsides. The unit is extremely adept at managing the vast array of plants in the state's three major climate zones—coastal, piedmont, and mountain—which contain multiple cool- and warm-season grass species. The soil is sandy in the state's eastern coastal areas and clay in its mountainous western portion, providing growing conditions for a variety of weeds.
In the coastal areas, the DOTcontends with warm-season grass species, such as bahiagrass, centipede, and bermudagrass. The vegetation management team has two priorities in this region: suppressing bahiagrass seedheads, and converting bahiagrass to centipede.
Bahiagrass produces seedheads all summer. “We can mow it, but three days later it will sprout another seedhead,” says Clemmer, a roadside environmental engineer for NCDOT's vegetation management team. “On average, these warm-season grass areas would require three to five costly mowings per year if we didn't apply herbicides.”
The second component of the warm-season grass management plan in eastern North Carolina is removing bahiagrass from areas pre-planted with centipede grass, which produces fewer seedheads and requires less maintenance. If left unmowed, centipede grass grows to only 4 to 6 inches, making it a popular choice for rights of way. By switching to centipede, NCDOT only has to mow one to two times per year, instead of the previous three to five.
To maintain cool-season grasses—such as tall fescue—in western North Carolina, NCDOT uses a plant growth regulator program to reduce the height of the grass. While tall fescue is an ideal cool-season grass species for erosion control, it can grow up to 4 feet, hampering visibility of road signs and hazards.
Without a herbicide to regulate its height, fescue would require five to seven mowings per year. By applying a herbicide with imazapic in March or April, NCDOT has reduced the number of mowings to four to six a year.
“Any money we save on mowing can go toward other aspects of our environmental projects,” says Smith, NCDOT's vegetation management supervisor. “Vegetation management is a dynamic science—there are always new projects to take on, but not always new money to fund them. We have to leverage our dollars as best we can.”
One project that benefits from lower mowing costs is North Carolina's wildflower program. NCDOT initiated the program on 12 acres of roadside in 1985 to support native wildflower growth while discouraging invasive plant species.
“The first years were trial and error,” says Smith. “There was no information on how to grow wildflowers from seed, so we had to learn which species would grow in North Carolina and what techniques would help them flourish.”