Herbicides help Illinois DOT control roadside weeds

Mowing is the standard method for eliminating weeds and woody brush from highway roadsides. The Illinois Department of Transportation (IDOT), however, has found herbicides to be a more effective solution.

Mowing plays an integral role in management of desirable grasses, but it has proven to be a costly and ineffective method of maintaining unwanted vegetation, according to IDOT’s Richard Maggi, a landscape architect. “Mowing doesn’t eradicate your vegetation problems,” he says. “It delays or hides them.”

A variety of roadside vegetation on Illinois’ more than 4,700 miles of roads makes weed and brush control challenging. Canada thistle, musk thistle, teasel, willow, box elder, elm and black locust grow along the highway.

The thistles and teasel, which are dominant in the Northwest, are noxious weeds that, by law, must be controlled because of the damage they can do to agricultural crops. To complicate things, IDOT must protect “ornamentals,” including oak, maple, ash, pear and Hawthorn.

Last year, the department began using Garlon 3A, by Indianapolis-based Dow Agro Sciences, to take care of weeds and brush without disturbing sensitive ornamentals. Maggi first applied a small amount of the herbicide in one location to evaluate its effectiveness. He found that it destroys thistle and teasel but is not “soil active.” In other words, it does not seep into the soil, so the ornamentals do not absorb it.

IDOT workers avoid spraying near ornamentals to prevent the herbicide from drifting onto them. In areas without ornamentals, Maggi uses Tordon 101M to manage Canada thistle, musk thistle and teasel. For large applications, crews perform “broadcast” applications with a truck-mounted spray system. Conventional hoses and handguns generally are used for smaller patches.

Maggi estimates spraying herbicides costs about $15 per acre, while mowing costs approximately $30 per acre. Moreover, the results have been better because herbicides are designed to be absorbed by the plant, thus killing it.

On the down side, herbicides do raise environmental concerns. Those applying herbicides must take into consideration wind, which can cause “off target” damage to private property, and high temperature, which can foster volatility in herbicides. Additionally, groundwater contamination can be a concern with soil active herbicides. However, if properly used, damage to the environment from herbicides is negligible, according to Maggi.

Finally, in addition to benefiting from the effectiveness and reasonable cost of its herbicides, IDOT has made vegetation management a safer job for many workers. Spraying need not be done repeated times like mowing, so workers reduce their exposure to high-volume, high-speed traffic.

-Peggy Caylor