Harvest weed seed control systems are similarly effective on rigid ryegrass

Harvest weed seed control (HWSC) systems have been developed to exploit the high proportions of seed retained at maturity by the annual weeds rigid ryegrass, wild radish, bromegrass, and wild oats. To evaluate the efficacy of HWSC systems on rigid ryegrass populations, three systems, the Harrington Seed Destructor (HSD), chaff carts, and narrow-windrow burning were compared at 24 sites across the western and southern wheat production regions of Australia. HWSC treatments were established at harvest (Nov.-Dec.) in wheat crops with low to moderate rigid ryegrass densities (1 to 26 plants m^-2). Rigid ryegrass counts at the commencement of the next growing season (Apr.-May) determined that HWSC treatments were similarly effective in reducing emergence. Chaff carts, narrow-windrow burning, or HSD systems act similarly on rigid ryegrass seed collected during harvest to deliver substantial reductions in subsequent rigid ryegrass populations by restricting seedbank inputs. On average, population densities were reduced by 60%, but there was considerable variation between sites (37 to 90%) as influenced by seed production and the residual seedbank. Given the observed high rigid ryegrass seed production levels at crop maturity it is clear that HWSC has a vital role in preventing seedbank inputs in Australian conservation cropping systems. Nomenclature: Bromegrass, Bromus spp. Roth BRODI; rigid ryegrass, Lolium rigidum Gaudin LOLRI; wild oat, Avena fatua L. AVEFA; wild radish, Raphanus raphanistrum L. RAPRA; wheat, Triticum aestivum L.