Evaluating Seed Shatter of Economically Important Prairie Weed Species

Abstract

The increasing occurrence of herbicide resistance, along with no new herbicide modes of action developed in over 30 years, have increased the need for non-herbicidal weed management strategies and tactics. Harvest weed seed control (HWSC) practices have been successfully adopted in Australia to manage problematic weeds. For HWSC to be effective, a high proportion of weed seeds must be retained on the plant at crop maturity. This 2-year (2014, 2015) study evaluated seed shatter of wild oat (Avena fatua L.), green foxtail (Setaria viridis L. Beauv.), wild mustard (Sinapis arvensis L.), and cleavers (Galium spp.) in an early (field pea, Pisum sativum L.) and late (spring wheat, Triticum aestivum L.) maturity crop in field experiments at Scott, Saskatchewan as well as producer fields (including canola, Brassica napus L.) in Saskatchewan. In producer fields, kochia (Kochia scoparia L. Schrad.) and wild buckwheat, (Polygonum convolvulus L.) were also investigated. Seed shatter was assessed using shatter trays collected once a week during crop ripening stage, as well as at two crop harvest stages (swathing, direct-combining). In the small-plot experiments, seed shatter differed among weed species, but was similar between field pea and wheat at maturity: ca. 30% for wild oat, 5% for cleavers, < 2% for wild mustard, and < 1% for green foxtail. Similar results were observed in producer fields: 22-30% for wild oat, and generally < 10% for the other species. Seed shatter of weeds in canola at swathing, including that of wild oat, was uniformly low (< 5%). Overall, seed shatter of wild oat occurred sooner and at greater levels during the growing season compared with the other weeds. Viability of both shattered and plant-retained seeds was relatively high for all species. Low seed shatter of green foxtail, wild mustard, cleavers, wild buckwheat, and kochia indicates that there is potential for these species to be controlled by HWSC practices. Due to the amount and timing of wild oat seed shatter, HWSC may not reduce population abundance of this grassy weed.