Don't Let Weed Seeds Hitchhike

Waterhemp is an aggressive and often resistant weed. ( Sonja Begemann )

Weeds are prolific, not only in seed production but distribution as well. Through a wide variety of vehicles, they spread far and wide, increasing their devastation with each new location.

“By far, human activities are the No. 1 source of weed seed transportation in ag systems,” says Bob Hartzler, Iowa State University Extension weed scientist. “Seventy years ago, crop seed was the most important way we moved seed around, but in today’s world with seed laws that has minimized that risk.”

Human-generated weed seed spread

While weed seeds certainly have their own ways in which to spread, humans by far are the biggest culprits when it comes to their longer distance reach. Check out a few of the most common ways weed seed spreads:

  • Likely the biggest way farmers unintentionally spread weed seed is moving equipment from field to field. “With something like waterhemp, one million seeds in a combine isn’t unlikely,” Hartzler says. “A study showed if you want to completely clean out a combine to eliminate weed seeds it would probably take two days, but if you finish a field and just run the combine to blow it out, that’ll probably eliminate three-quarters of the seeds, and if you take half an hour to clean areas you know seeds will be you can likely reduce seeds by about 95%.”
  • Pollinator plots and bird seed can contain unwanted weed seed. “Does the bag of seed your buying have just one thing or numerous ingredients,” says Kevin Bradley, University of Missouri Extension weed scientist. “Having just one kind of seed is much safer because when you clean seed you have just one size to watch and keep weed free.”
  • Sourcing grass and other forage-type seeds from other states. “It’s not that any state is doing it intentionally, but if seed is coming from a state with something like Palmer amaranth, use caution,” Bradley says. “And it’s always a good idea to use a reputable brand name of seed.”
  • To a limited degree, manure. “We know spreading manure can introduce weed seed, but we don’t haul manure that far, so it’s not going to be weed seed crossing state lines,” Hartzler says. However, if it’s manure from a farm you don’t own, it could introduce a small number of new, resistant biotypes.

By taking proper precautions when moving machinery such as tillage equipment, planters and especially combines and minding other best practices, you can greatly reduce man-made weed seed spread.

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