ABSTRACT
Clean production fields look remarkably homogeneous, as anyone who remembers the halcyon days of herbicide-resistant crops in the late 1990s can attest. A scouting trip through the northern US Corn Belt during that time would have revealed row after uniform row of maize and soya beans with barely a weed in sight. Twenty years later, the view is much changed. Completely weed-free grain fields are the exception, not the norm. Driving a transect east from central Illinois, through Indiana and into Ohio this past summer, I saw weeds in nearly every field I passed, and these infestations were true to Tolstoy’s allegory in their unending variety. Some fields held many weeds of a single species spread throughout the field in a diffuse, consistent pattern. Other fields showed tight patches of multiple weed species. Novel weeds invaded from the field margins to others. Understanding the sources of diversity of weeds in agricultural fields is central to developing successful long-term weed management approaches. In an era where herbicide resistance has increasingly become common, this understanding
is as critical for ‘conventional’ growers with herbicide-dependent weed management programmes as it is for growers who, for a variety of reasons, have relied less or not at all on herbicides.
