Artemisia biennis (biennial wormwood) control is influenced by plant size and weed flora at time of herbicide application

Artemisia biennis has become a major weed of several crops within the northern Great Plains of the US and Prairie Provinces of Canada. It is expanding its habitat range and is now a problem weed across the North Central region of the United States. Field and greenhouse studies were conducted to evaluate the role of weed size, weed flora, and herbicide dose and timing on control efficacy. Two separate field studies were conducted in close proximity to evaluate the effect of late post-emergence herbicide application timing on A. biennis control. The first study had an infestation of Xanthium strumarium and the second study had an additional infestation of Amaranthus retroflexus. In both field studies, X. strumarium and A. retroflexus were substantially taller than A. biennis at each application timing. When X. stumarium was present, A. biennis control was 50-90% with glyphosate, and 40-75% with bentazon. When A. retroflexus was present, A. biennis control with either bentazon or glyphosate was greater than 82%. Greenhouse studies evaluated the effect of dose of bentazon, glufosinate, and glyphosate on control of various growth sizes of A. biennis seedlings ranging from 6 to 47 cm. Glyphosate applied at 840 and 1680 g ae ha−1 provided greater than 92% control of all sizes of A. biennis seedlings, while bentazon provided at least 80% control of A. biennis up to 20 cm tall. Control with glufosinate was generally poor regardless of seedling size or herbicide dose.