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 negative impacts of herbicides on human health and the environment have led growers to look for alternative non-chemical weed control. Harvest weed seed control (HWSC) is a non-chemical weed control tactic based on reduction of seed return of primarily annual weed species to the soil seed bank that has been successfully adopted by farmers in Australia. The strategy is to collect and/or destroy the weed seeds in the chaff material during harvest using chaff carts, bale direct system, integrated impact mills, windrow burning, chaff tramlining and chaff 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 crop canopy height and coincidence of weed and crop maturity. Initial research efforts in Europe have found that there 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 to e.g., Australia. The challenges include that crop and weed maturity are not concomitant which results in lower seed retention values at crop harvest. In addition, there has not been a concerted research effort to evaluate HWSC systems in European cropping systems. Until now, research on HWSC in Europe mainly focused on the rate of weed seed retention in specific weed species. For HWSC to contribute to the mitigation of herbicide resistance and add to the toolbox of integrated weed management measures, there is an urgent need to take HWSC research to the next level. Although HWSC is not functionally equivalent to herbicide application, it may help to reduce herbicide inputs in the long-term when used in combination with other tactics. Future research and development should focus on the evaluation of HWSC strategies for the practical adoption of these tactics in European cropping systems.