Herbicide Resistance Update

Although herbicides have been an important component oflowa crop production for more than 30 years, the degree of reliance on these ag chemicals has increased significantly in the past decade. The primary cause of this increased reliance is the decrease in the use of tillage as a weed management tool. While this has benefits in terms of protecting soil from erosion and decreasing energy use, it does increase the potential for selection of herbicide resistant weeds. Herbicide resistance is defined as the inherited ability of a weed to survive a herbicide dose that kills the native population of that species. The two important points of this definition are 1) the ability to survive the herbicide is genetic and passed along to progeny, and 2) the native population is controlled by the herbicide. It is likely that herbicides will remain the primary weed management tool used in crop production for the forseeable future, thus it is critical that they be used in a manner that preserves there utility. This paper will address the following questions concerning herbicide resistance: 1) How does resistance develop? 2) How widespread is resistance? 3) How long will resistance persist once it occurs? 4) How do you prevent resistance? and 5) Will weeds develop resistance to Roundup