Dairy production systems rely on alfalfa as a key component in their ration. Alfalfa provides a high yielding and quality forage as well as key ecosystems services as part of a rotation with annual crops. One of the under-valued services is weed control as it has been documented that alfalfa stands can reduce weed populations if managed correctly (e.g., Clay and Aguilar, 1998; Goplen et al., 2017). Few annual weeds can compete with alfalfa stands and do not germinate unless alfalfa stand density is below recommended levels or the alfalfa is stressed due to lack of precipitation or pest (insect disease) damage. What few annual weeds that emerge are not able to produce viable seeds due to the frequent harvest interval present in a dairy system (every 28 to 35 days). For example, giant ragweed, a highly competitive annual weed that is capable of germinating throughout the spring, had emergence reduced by 59% when grown under alfalfa compared to corn and didn’t produce any viable seeds in a research project in Minnesota (Goplen et al., 2017). Unfortunately established alfalfa systems are currently being invaded by waterhemp (Amaranthus tuberculatus (Moq.) J.D. Sauer), a weed species that has the potential to germinate and produce viable seed within this
competitive forage system.