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A Potential Tool to Control Herbicide Resistant Weeds During Harvest?

Posted by Judit Barroso, Oregon State University | January 13, 2021

Harvest weed seed control (HWSC) is an innovative, non-chemical tool that has proved successful in Australia to control herbicide-resistant weeds. HWSC takes advantage of weed seed retention at crop maturity to control the harvested weed seeds. In a common harvest, weed seeds are collected, threshed, separated from the grain, and included most probably in the chaff fraction that is usually ejected behind the combine, spreading weed seeds throughout fields and perpetuating weed issues.

In my opinion, two of the most promising HWSC practices for the semi-arid region of the Pacific Northwest (PNW) are chaff lining and integrated impact mills. These two practices target weed seeds in the chaff in two different ways. Chaff lining (image 1) consists of funneling the chaff into a narrow, 10-12 inch row behind the combine, where the residue is left to overwinter. Weed seed decay and predation can be accelerated in the chaff row since seeds are buried deep within the light residue. A follow-up herbicide application in chaff lines is often required to kill any emerging weeds. In contrast, integrated impact mills (image 2) pulverize (destroy) weed seeds in the chaff before it is spread behind the combine. Impact mills are generally considered the ultimate HWSC technique since the efficacy of seed destruction is very high (>95%).

Image 1. Funnel at the back of a combine to direct the chaff into a narrow line.

Integrated impact mill on back of combine.Image 2. Integrated impact mill at the back of a combine to pulverize the weed seeds in the chaff.

Combine separating chaff from straw. Image 3. Baffle at the end of the residue process inside the combine to separate chaff from straw.

Both HWSC practices require the combine to be set up (inclusion of a baffle, image 3) to separate the chaff and straw and so keeping the weed seeds in the chaff stream. Once this retrofit is conducted, chaff lining requires a simple chute to be fitted to the rear of the combine to direct the residue into a narrow line on the ground. Adding a chute is low cost and is often constructed and fitted on-farm. Integrated impact mills are significantly more expensive and require commercial modifications to fit them into a combine. In addition to the higher cost, the use of integrated impact mills could reduce the life expectancy of the combine.

Weed scientists have started to study the efficacy of these HWSC tools to control the most important weed species in the region. We are aware of certain skepticism related to these practices and we would appreciate your feedback to help guide our research and to fuel adoption of these techniques. Do you see either method being adopted in the region? Do you think these tools could be practical on your farm?

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