Opportunities and challenges for harvest weed seed control in European cropping systems

The rapid increase of herbicide resistance in some of the most problematic annual weeds, and potential negativeimpacts of herbicides on human health and the environment have led growers to look for alternative nonchemical weed control. Harvest weed seed control (HWSC) is a non-chemical weed control tactic based onreduction of seed return of primarily annual weed species to the soil seed bank that has been successfully adoptedby farmers in Australia. The strategy is to collect and/or destroy the weed seeds in the chaff material duringharvest using chaff carts, bale direct system, integrated impact mills, windrow burning, chaff tramlining andchaff lining or other methods of targeting the chaff material containing the weed seeds. Two biological characteristics are exploited with successful HWSC: the level of weed seed retention at crop harvest above cropcanopy height and coincidence of weed and crop maturity. Initial research efforts in Europe have found thatthere are several candidates for HWSC among weed species with a high importance in European cropping systems. The highest potential has been found for weeds such as Galium aparine, Lolium rigidum and Silene noctiflora.However, there are several challenges for the adoption of these systems under European conditions compared toe.g., Australia. The challenges include that crop and weed maturity are not concomitant which results in lowerseed retention values at crop harvest. In addition, there has not been a concerted research effort to evaluateHWSC systems in European cropping systems. Until now, research on HWSC in Europe mainly focused on the rateof weed seed retention in specific weed species. For HWSC to contribute to the mitigation of herbicide resistanceand add to the toolbox of integrated weed management measures, there is an urgent need to take HWSC researchto the next level. Although HWSC is not functionally equivalent to herbicide application, it may help to reduceherbicide inputs in the long-term when used in combination with other tactics. Future research and developmentshould focus on the evaluation of HWSC strategies for the practical adoption of these tactics in Europeancropping systems.