An experiment was conducted to determine the population dynamics of barnyardgrass under a range of weed management treatments in glyphosate-resistant (GR) cotton in Australia. These treatments consisted of glyphosate herbicide only (Glyphosate only), glyphosate herbicide plus a combination of conventional or integrated weed management practices (Glyphosate IWM), glyphosate herbicide plus a reduced residual herbicide program (Glyphosate Res.), glyphosate herbicide plus a grass herbicide (Glyphosate Grass), and a combination of conventional weed management practices (IWM only). The experiment investigated the effects of weed management on the weed seed bank, weed emergence patterns, and weed populations. After three years, all treatments resulted in commercially acceptable control of barnyardgrass. However, treatments containing soil-applied residual herbicides proved more effective over the period of the experiment. Seed bank reductions were in the order of 100-fold over the period of the experiment for treatments that received residual herbicides compared to 10- to 20-fold reductions for treatments that did not. The experiment highlighted the importance of early-season weed control, as well as the importance of an integrated approach to weed management with residual herbicides to control later-emerging weeds in GR cotton.

Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG, cotton, Gossypium hirsutum L