Pigweed species (Palmer amaranth and waterhemp) have become increasingly difficult for Kansas farmers to control because resistance to herbicides, such as glyphosate and ALS-inhibitors (Group 2) is common. Resistance to PPO-inhibiting herbicides (Group 14) and 2,4-D has also been reported. Furthermore, it is expected that the occurrence of resistance to growth regulator herbicides like 2,4-D and dicamba will increase in the near future due to their use in Enlist and Xtend soybeans. These developments have led to reliance on Liberty to control pigweeds in season. Other states have reported Palmer amaranth populations with resistance to glufosinate , and it is likely resistant populations exist in Kansas. In addition, herbicide applications made in hot, dry conditions to large pigweeds are resulting in unacceptable control. A greater understanding of the impact of environmental conditions on pigweed control and the best way to measure those conditions will help growers improve weed control. Effective herbicide programs will likely require sequential applications. However, there is little data or economic analysis to support recommendations regarding the details of sequential herbicide applications. This project seeks to identify application characteristics and environmental conditions that result in the greatest weed control and economic return. In addition, this project will contribute to sample collection and screening for resistance to key herbicides used in soybean production systems.