Hitchhiking weed seeds spread for miles


When you take a four-wheel drive out for a spin, you could be bringing home more than memories.

The Weed Science Society of America is spotlighting work by Montana State University that focuses on the role vehicles play in the spread of invasive weeds.

The researchers found vehicles are routinely transporting invasive weed seeds. The seeds can stow away on tires, bumpers, wheel wells or the underside of a vehicle. And sometimes they travel great distances before falling off in a new locale. As weed seeds sprout and grow, they can crowd out native plants, disrupt native ecosystems and wildlife habitats, and reduce crop yields.

Key Points

Weed seeds can travel for miles hitching a ride on cars, trucks and ATVs.

Distance is no barrier to stopping the spread of weed seeds.

Off-road travel increases the risk of spreading weed seeds.


“Take a look at the many types of weeds growing along most any roadside, and you’ll get a big clue about the role vehicles play,” says Lisa Rew, a member of the Weed Science Society of America with Montana State. “With an estimated 4 million miles of roads crisscrossing the U.S., and 256 million registered vehicles, even a few weed seeds per car can make a significant impact on the spread of weeds.”

Research findings

Montana State researchers measured the number of seeds picked up by a variety of vehicles and the distance traveled before the seeds fell off. Among their key findings:

Seed volume is seasonal. The study showed thousands more seeds per mile were transported by vehicles during the fall than in the spring.

Moisture matters. Wet conditions make it easier for a vehicle to pick up seeds and carry them for miles down the road. Tests conducted at military installations showed Humvees picked up 14 times more seed when conditions were wet, while tanks picked up 26 times more.

Distance is no barrier. The distances seeds can travel can be long. When researchers examined vehicles over several distance intervals, they found even at the 160-mile mark, many seeds stayed attached. Rew says if seeds are lodged in the mud that dries on a vehicle, they can travel almost indefinitely, or at least until it rains again and the road is wet. Scientists consider that bad news. When vehicles transport seeds long distances, it increases the likelihood that weeds will be spread into areas where they don’t yet occur.

Off-road travel increases the risk. Outdoor sports enthusiasts trucking to remote trailheads or riding ATVs off the beaten path are at special risk for spreading weeds. Researchers found vehicles picked up almost 20 times more seeds off-trail than on-trail.

Prevent spread

Researchers say just washing your vehicle frequently, especially after off-road and off-trail travel or driving along roads bordered with heavy weeds, could help prevent the spread of weeds. Both the U.S. Forest Service and U.S. Department of Defense routinely do that to reduce the risk of transporting weed seed.

Vehicles washed once for six minutes, or two to three times for three minutes each, were judged most weed-free. Five portable commercial wash units were tested, and each performed similarly, regardless of the water pressure or amount of water used. But four of the units with undercarriage washers, as well as pressure hoses, did make it easier to remove dirt.

As an added measure, landowners in areas where high-risk invasive weeds are growing are advised to close the area off to traffic when the ground is wet. Researchers say doing so will dramatically reduce the risk of transporting weed seeds to new sites and 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 says.

See weedeco.msu.montana.edu.

This article published in the January, 2012 edition of THE FARMER-STOCKMAN.

All rights reserved. Copyright Farm Progress Cos. 2012.