The primary reason for controlling weeds during crop production is to eliminate crop yield losses due to competition between the crop and weeds. However, the majority of Iowa farmers strive to obtain higher levels of weed control than necessary to protect crop yields from weed competition. In most instances, the rationale for this contradiction is the concern over the impact of weed seed production on future weed populations. Most weed species are prolific seed producers, and seed dormancy enables weed seeds to survive for long periods of time. Thus, it is true that weeds allowed to go to seed in a field can impact weed populations for the next seven years - if not longer. Less clear, however, is whether the potential increase in weed population poses a real threat to the effectiveness of current weed management strategies.