Road maintenance involves a variety of activities such as road grading; roadside brushing and mowing; installation, maintenance, replacement, and removal of drainage structures; ditch cleaning; maintenance and replacement of structures such as cattle guards, gates, and signs; and crushing, storing, and placing of aggregate. Each of these activities is defined in appendix A.

Roads on public lands are high-risk sites for the introduction and spread of noxious and invasive plants. Transporting seeds and plant parts by vehicles (Lonsdale and Lane 1994) and removing vegetation and mixing soil during road construction and maintenance provide ideal conditions for the introduction, germination, and establishment of weed seeds. Road corridors are also prolific sources of weed seeds that may be carried to other locations (Tyser and Worley 1992) or that may colonize adjacent vulnerable habitats.

Road grading typically moves road surface material up and down the road system. This process disturbs soil and vegetation on the roadway and shoulders, transporting soil and gravel that may carry weed seeds or vegetative propagules. No published studies of the transport of seeds during grading have been completed, so it is not known how far weed seeds may be transported after they have been picked up by the grader's blade. The freshly graded road provides a disturbed soil seedbed suitable for weed germination when the seeds' moisture and temperature requirements are met. Grading a series of roads without washing the blade may transport weeds from one road to the next.

Cleaning roadside ditches also moves soil from place to place, creating an ideal seedbed by disturbing soil and removing competitive, desirable vegetation.

Equipment used to maintain road drainage structures can spread weeds by transporting soil and weed seeds from one culvert to another. Seeds from equipment can be deposited in stream crossings and washed downstream, creating infestations along the riparian corridor. Treatment of weeds in riparian zones is difficult and may require use of expensive techniques, such as hand removal.

When brush is cut along the roadsides, weed seeds are transported on the mower head. No studies of the relationship between road brushing and weed seed dispersal have been published. It is clear that weeds from other locations can be introduced to a work site on unwashed equipment. Excavators, road graders, ditch diggers, and other road maintenance equipment are often used in highly disturbed settings infested with noxious or invasive plants, providing ample opportunity for seeds to adhere to the machinery.

Since seeds and vegetative fragments are present in the soil at infested locations at all times of the year, road maintenance and other soil-disturbing activities can transport weeds at any time of the year—not just when plants are setting seed.

Stockpiles of crushed aggregate often become infested with noxious weeds, such as spotted knapweed. Weed seeds may be brought in on unwashed rock-crushing equipment and mixed into the aggregate during operations. Weeds from adjacent infested areas may also infest the aggregate stockpile. Seeds produced by infestations on the stockpile are transported with the aggregate when it is hauled and placed on roads.

Strategies for managing noxious weeds depend on the characteristics of the weed species present, the size and configuration of the infestation, the habitat in which the infestation is found, and local attitudes about weed management methods.

In general, managing weeds can be compared to fighting fires (Dewey 1996). In both cases, the work includes prevention, early detection and control, management, and restoration. Prevention is the most effective and least expensive weed management strategy. Once a species has been introduced to a site, early detection and control or eradication is the next best plan of action. When a species has become well established in an area, the strategy must be to contain and control the infestation. This is accomplished using integrated weed management techniques, including biological control agents, herbicides, manual and mechanical techniques, and restoration with desirable vegetation. Small infestations outside the perimeter of the main infestation should be detected early and eradicated, if possible, much as spot fires outside the main fire line are detected and put out.

Linear roadside weed infestations are similar to long, thin wildland fires and should be controlled before they cover large blocks of land.

Introduced as an ornamental from Asia, saltcedar invades riparian
habitats throughout the American West. It releases salt into the
soil, making the soil unsuitable for native species.
—Photo by Steve Dewey, Utah State University.
Image 1624020 courtesy of Forestry Images .