Giant chickweed (Myosotan aquaticum), a native species of Europe, was thought to predominately inhabit moist, natural areas of Wisconsin. In recent years its presence has been confirmed in perennial crops in Pierce, Green, St. Croix, Lafayette, Grant, Columbia, Sauk, and Shawano counties. Due to morphological similarities between the chickweed species, presence and distribution of giant chickweed has likely been underestimated in Wisconsin. The objective of this study was to develop classification methods for taxonomic separation from other chickweeds in agronomic settings and to provide preliminary data on chemical control in alfalfa and pastures.