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%).