Can your combine kill weeds?

By Greg LaBarge, Ohio State University Extension agronomist

Combines are traditionally thought of as one way to spread weeds from one field to the next. When we started seeing Palmer amaranth in Ohio, at least one infestation was traced to a combine purchased from the south. But maybe we need to rethink this notion that they only spread weeds. The headline in Crop and Soils Magazine, “From Spreader to Predator: Killing Weed Seeds with the Combine,” caught my attention. The research was initially done in Australia and has been adopted by 80% of that country’s farmers. 

Harvest weed seed control (HWSC) is the name of the concept. The concept is basic, using the combine to remove, concentrate or kill weed seeds harvested with the crop. Two goals can potentially be met. One, we reduce the seed bank. Two, by destroying or removing seed produced by escapes, HWSC can aid in herbicide resistance management. HWSC is not a standalone control method. It must be used as part of an integrated weed management approach using chemical, mechanical and cultural tactics.

There are six HWSC methods currently in use on Australian farms. All methods are effective but vary by combine modification, expense, logistics, and other considerations. Some methods are relatively simple do-it-yourself kits, while others have a higher price tag with additional equipment and substantial combine modifications. Common to most methods is adjusting the combine so weed seed exits the combine in the chaff rather than the straw fraction. With proper adjustment, 90% of weed seed will go out in the chaff.

The methods used have three general outcomes for weed seed. The weed seed is concentrated in the field where future treatments are made, is ground up before exiting the combine, or collected and moved offsite. U.S. research on HSWC methods is becoming available with on-farm proof of concept studies. For example, two Virginia studies focused on common ragweed in soybean showed a 26% and 43% reduction in weed density after the first year. Italian ryegrass was reduced by 69% in the wheat crop after HSWC use in Virginia. In addition, a four-year study on Italian ryegrass found a >90% reduction in weed density using HSWC with herbicides in Texas. Modeling in U.S. corn-soybean rotations show HSWC to be effective, greatly reducing weed seed banks in just four to five years of use. 

Weed management continues to evolve, and the combine may be a tool that fits into your management system. If you are interested in more details on HSWC, the entire article is found at

It is essential to finish this article by recognizing that HSWC concepts started with a farmer/researcher collaboration in Australia. Some of the most rewarding research work I have been involved in started from a farmer’s question. In our C.O.R.N. newsletter, you may have noticed our announcement of new researchers and Extension specialists at The Ohio State University College of Food Agriculture and Environmental Sciences. You can help them as they get started in the state by reaching out to them about issues on your farm. One opportunity to meet these new staff members in person will be during the Conservation Tillage and Technology Conference, March 8 and 9 in Ada. We are planning a session entitled “Our new crop of Extension specialists.” I hope you can join us.

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