Start Clean, Stay Clean

Mitigating Weed Seeds at Harvest

Effective weed control is a priority for farmers, and one way to aid in that effort is managing weed seed. Destroying weed seeds before they spread is one approach gaining momentum in the industry. Now, more farmers are facing what to do to rid their fields of weed seeds at harvest. But what happens when a weed manages to get away and survives through harvest? One waterhemp plant can produce more than one million seeds per plant, so imagine the weed problems that follow.

Bill Johnson, Ph.D., Purdue University weed scientist, says the number one action farmers can do in their fields is clear: “Control the weeds so they don’t go to seed.” But when that weed gets away, he says the next best practice would be cleaning the seed after it’s harvested. Some methods for cleaning soybean seeds are gravity separators and air screen cleaners.

Researching Effective Control

Farmers in Australia have dealt with herbicide resistance for decades, and part of their approach to manage resistant weeds is to destroy weed seeds at harvest using a variety of technologies. While these methods may not yet be common in the U.S., at a minimum, farmers stateside can understand the theory behind weed seed control to understand what might be possible here.

In the meantime, University of Arkansas, Virginia Tech and USDA Agricultural Research Service locations in Beltsville, Maryland and Urbana, Illinois are all researching weed seed control methods used in Australia, like the Harvest Weed Seed Control (HWSC) including chaff cart removal, narrow windrow burning, baling and the Harrington Seed Destructor

Best Practices for Weed Control

Managing the weed seed bank prevents weeds from becoming an issue. Natural predators like insects and mice may help to reduce the weed seed population in the soil, but they can’t do all the work. Some suggested practices for weed control are:

  • Control weeds before they go to seed.
  • Rotate crops — don’t give weeds time to adapt to one crop.
  • Avoid deep tillage — don’t let seeds be preserved in the soil profile.
  • Plant cover crops — give weeds competition with vigorous crops.
  • Modify harvest equipment — remove weed seeds from the field by altering equipment so seeds are destroyed immediately.

Farmers have other options at various weed growth stages. Before weeds grow taller than four inches, apply burndown herbicides, clearing the field of existing weeds. Apply pre-emergence herbicides offering residual control for weeds that have not yet come out of the ground. Stopping the weeds in their tracks prevents problems later in the season and reduces the need for HWSC. Also, soybeans no longer compete with the weeds while growing, improving yields.

Planning for the Future

When considering what farmers can do going into harvest this season to prevent weed-takeover next season, Johnson advises, “Assess your weed control programs now while you can still see the results of this year’s weed control activities. This will help you plan weed management tactics for next year, which should include a combination of chemical and cultural practices.” Combining chemical and cultural practices is the most sustainable method of weed control that we have right now, so let’s use it to our advantage.

While methods of HWSC are still in testing, it’s important to think about weed seed control practices in the U.S. that will be sustainable and effective long-term. The practices outlined above would, in theory, reduce the opportunity for herbicide resistance to develop because there will be fewer weeds that will need to be controlled with herbicides. The issue of herbicide resistance, like weeds, will only grow, and any of these methods may be an answer to the problem.


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