To prevent the spread of weeds, researchers recommend that you wash your vehicle frequently, especially after driving off-road or off-trail or along roads bordered by high densities of weeds. Both the U.S. Department of Defense and the U.S. Forest Service routinely use that technique to reduce the risk of transporting invasive species.

Montana State researchers evaluated the ideal duration and number of washes needed to remove weed seeds. Vehicles washed once for six minutes or two to three times for three minutes each were judged to be the most seed-free. Five portable commercial wash units were tested, and each performed similarly, regardless of the water pressure or the amount of water used. Four of the units had undercarriage washers as well as pressure hoses, which made removal of dirt from the underside much easier.

As an added measure of protection, land managers in areas where high-risk invasive species are growing are advised to close the area to traffic when the ground is wet. Doing so will dramatically reduce the risk of transporting weed seeds to new sites and also reduce future weed management costs.

"Understanding how vehicles spread weeds and the steps we can take to intervene can help us reduce weed seed dispersal and reduce the likelihood of devastating new invasions that can be costly to eradicate," Rew said.