Managing the evolution of herbicide resistance.

BACKGROUNDUnderstanding and managing the evolutionary responses of pests and pathogens to control efforts is essential to human health and survival. Herbicide-resistant (HR) weeds undermine agricultural sustainability, productivity and profitability, yet the epidemiology of resistance evolution-particularly at landscape scales-is poorly understood. We studied glyphosate resistance in a major agricultural weed, Amaranthus tuberculatus (common waterhemp), using landscape, weed and management data from 105 central Illinois grain farms, including over 500 site-years of herbicide application records. RESULTSGlyphosate-resistant (GR) A. tuberculatus occurrence was greatest in fields with frequent glyphosate applications, high annual rates of herbicide mechanism of action (MOA) turnover and few MOAs field(-1) year(-1). Combining herbicide MOAs at the time of application by herbicide mixing reduced the likelihood of GRA. tuberculatus. CONCLUSIONSThese findings illustrate the importance of examining large-scale evolutionary processes at relevant spatial scales. Although measures such as herbicide mixing may delay GR or other HR weed traits, they are unlikely to prevent them. Long-term weed management will require truly diversified management practices that minimize selection for herbicide resistance traits. (c) 2015 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.