Herbicide-resistant weed species have become an increasing problem in many cropping systems, due in large part to the widespread reliance on herbicides as a primary method of weed management. Herbicide resistance has been defined as the inherited ability of a plant to survive and reproduce following exposure to a herbicide dose normally lethal to the wild type (Weed Science Society of America 1998). Weed resistance to herbicides has been confirmed in 156 species (94 dicots and 62 monocots) worldwide, most commonly to acetolactate synthase (ALS) inhibitors, triazines, or acetyl-coenzyme A carboxylase (ACCase) inhibitors (Heap 2003). Resistance to herbicides has been selected for in several weed species found in Wisconsin, including resistance to ALS inhibitors in eastern black nightshade (Solanum ptycanthum) (Volenberg et al. 2000), giant foxtail (Setaria faberi) (Volenberg et al. 2001), and green foxtail (Setaria viridis) (Volenberg et al. 2002), resistance to ACCase inhibitors in giant foxtail (Stoltenberg and Wiederholt 1995) and large crabgrass (Digitaria sanguinalis) (Wiederholt and Stoltenberg 1995), and resistance to triazine herbicides in several broadleaf weed species (Stoltenberg 1995).