Pennsylvania: Worst Weeds Can Move with the Combine

    Uncontrolled weeds in an industrial hemp field. Photo: Erin Burns, Michigan State University

    An ounce of prevention is worth a pound of cure when it comes to weed management—especially for herbicide resistant weeds. Resistant weeds cause significant yield loss and increased production costs and are becoming a bigger problem every year in Pennsylvania.

    Our most problematic herbicide resistant weeds, like marestail, waterhemp, and Palmer amaranth, can easily spread from one field or one farm to the next, as seeds get trapped in the combine and hitch a ride field-to-field at harvest.

    So, it is important to be proactive to prevent this seed spread. You should have a plan going into the harvest season, including the appropriate order to harvest fields, and equipment-cleaning protocols. GROW (Get Rid Of Weeds), a publicly-led network that provides resources and tools for implementing integrated weed management (IWM), suggests a few simple ways to prevent the spread of weeds with equipment:

    • Scout fields before harvest, and identify which fields have noxious weeds
    • Harvest and/or till herbicide-resistant weed-infested fields, or portions of fields last
    • If the combine or tillage equipment entering a field has recently been in a field with herbicide-resistant weeds, clean the equipment, or use different equipment if it is available
    • Carefully and completely clean used equipment upon purchase
    • Start cleaning the combine from the top, and moving from the header backward
    • Use your air compressor installation to remove as many weed seeds from the combine as possible, including the rock trap, grain auger, and tailings processor
    • Deep clean the combine following the Straw Bale Methodology when moving from fields infested with herbicide resistant weeds, and at the end of the year

    You can read more, including a case study about waterhemp movement in southeastern Pennsylvania, online.

    Once harvested, fields should not be abandoned until next spring. Marestail, a winter annual weed, will thrive in the fall after corn or soybean harvest; fall burndown in marestail-infested fields is essential .

    And, although waterhemp and Palmer are summer annuals, they can still potentially set seed with favorable weather, even if the cutter-bar knocked them back to only a few inches tall. It is important to continue to scout fields and take action if necessary.

    Lastly, planting cover crops after any necessary burndown this fall can substantially improve weed management. Research shows that high-biomass cover crops, like cereal rye, can not only reduce the number of weeds that emerge from seed in the spring, but delay weed germination and growth, making it easier to spray while weeds are smaller and more susceptible to herbicides. A thick cover crop mat can extend this weed suppression well into the growing season.

    Preventing weed spread is an important tool in the integrated weed management (IWM) toolbox, and cleaning equipment is worth the time and effort today to prevent a serious management challenge in the future.

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