By Clarabell Probasco

One of the hardest battles growers fight throughout the crop-growing season is against unwanted weeds. Weed populations can quickly become a significant problem and lead to yield reduction and poor field health. Being on the forefront of the battle against weeds can help growers better prepare for the upcoming growing season.

One of the best places to start is by implementing weed seed control methods during harvest.

Combines play a large role in spreading weed seed across a crop field. Harvest weed seed control (HWSC) implements management tactics that assist in preventing weed seed present at harvest from entering the field’s weed seedbank. Reducing these weed seedbank numbers leads to less pressure from future weed populations in that crop field.

HWSC methods are growing increasingly important as the number of herbicide-resistant weed populations continue to grow. Using multiple types of control methods provides more avenues to reduce weed populations and avoids creating additional herbicide resistance issues. These methods can be implemented to become an active piece of an integrated pest management strategy on farming operations.

HWSC tactics

HWSC techniques include using:

One of the most applicable techniques for the Midwest is arguably the use of chaff mills. Chaff mill devices are placed on the rear of the combine and allow the weed seed to be separated from the chaff. Weed seed travels through a rolling cage mill that damages the seeds and makes them nonviable for germination. This method also is commonly referred to as weed seed destruction.

Another proven HWSC method for the Midwest is the use of chaff lining. With this method, a specialized chute is placed on the rear of the combine, which then places the chaff in a narrow strip about 12 to 20 inches wide in the field. The goal of placing the chaff in a narrow row is to create a mulching effect. Weed seed placed inside the chaff line has a lower likelihood of germinating, as well as stunted and delayed growth, when compared with weeds outside of the chaff line.

Herbicide applications also can be made directly to the concentrated areas of chaff. This reduces the overall need for herbicide usage in the cropping field.

The success of these management tactics heavily relies on the ability of the present weeds in the field to retain their seeds until harvest takes place. Seed retention rates can greatly vary from one weed species to the next.

Rather than relying solely on HWSC methods, these tactics should be combined with additional weed-control measures that create yearlong effective weed control, such as the use of herbicides. Although these management tactics may seem like a newer concept, they have proven to be successful in reducing weed seed populations for decades in crop fields worldwide.

Consider HWSC

When facing difficult weed populations in a field, be sure to consider the opportunities of implementing a harvest weed seed control tactic into your farming operation. If additional questions arise, be sure to reach out to your local Iowa State University Extension field agronomist.

Probasco is a former Iowa State University Extension field agronomist.