Occasional mouldboard ploughing slows evolution of resistance and reduces long-term weed populations in no-till systems

The greater reliance of no-till (NT) cropping systems on herbicides can exacerbate weed resistance to herbicides and an occasional mouldboard plough (MB) has been proposed as a useful weed control technique, because it buries the weed seeds at a depth where most cannot germinate.In this study we use the Polygenic Evolution of Resistance To Herbicides (PERTH) model to predict whether NT systems have a higher risk of annual weeds developing resistance to soil-residual herbicides such as trifluralin compared to tillage-based systems. We also test the hypothesis that an occasional MB once every 4–8years will slow the overall development of resistance by ‘resetting the resistance clock’ and decreasing resistance levels to those of a susceptible (untreated) population. Finally, we analyse how our results vary depending on weed dormancy and the burial and lifting efficacy of the MB, key aspects of the occasional MB strategy.The PERTH simulations showed that the use of an occasional strategic MB slowed the development of resistance, but did not fully “reset the resistance clock” to susceptible population levels. The development of resistance was delayed appreciably with regular use of the MB. When we assumed higher weed seed predation and herbicide efficacy in the NT system, weed control improved markedly, although the rate of evolution of resistance to the soil residual herbicide was little changed. Higher seed dormancy resulted in slower development of resistance. Occasional use of the MB for weed control relies on a high seed burial efficacy, and the less frequent the MB, the greater the efficacy of burial required; more research on this aspect is required as it is so critical. There are likely to be regional and local issues and environmental and economic considerations that influence how often the occasional strategic MB is used, if indeed at all, but these results indicate that even very occasional use of the MB may be of benefit as a weed management option.