Yellow foxtail (Setaria pumila) reduces establishment of alfalfa interseeded into corn

Authors: SHAHEB, RAYHAN - University Of Wisconsin; Grabber, John; KOHMANN, MARTA - University Of Wisconsin; RENZ, MARK - University Of Wisconsin

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2025
Publication Date: 3/12/2025
Citation: Shaheb, R., Grabber, J.H., Kohmann, M., Renz, M. 2025. Yellow foxtail [Setaria pumila] reduces establishment of alfalfa interseeded into corn. Weed Science. https://doi.org/10.1017/wsc.2025.9.
DOI: https://doi.org/10.1017/wsc.2025.9

Interpretive Summary: Establishing alfalfa by interseeding it into a corn silage companion crop is a new cropping practice that can be used by farms to increase the production of high-quality forage and reduce the risk of nutrient and soil loss from cropland. High populations of pests, especially weedy annual grasses like yellow foxtail, can lead to poor establishment of alfalfa under corn. Our goal in this study was to identify a threshold for initiating control of annual grasses to ensure good establishment of alfalfa under corn. Our results suggest that yellow foxtail populations should be kept below 5 plants per square foot during establishment to obtain recommended densities of alfalfa close to 20 plants per square foot that are needed to maximize alfalfa forage production the following year. This research provides crucial information to guide control of annual grasses in this intercropping system.

Technical Abstract: Interseeding alfalfa (Medicago sativa L.) soon after planting a corn (Zea Mays L.) silage companion crop in early May is a novel approach that increases the production of high-quality forage and reduces the risk of nutrient and soil loss from cropland. Observations made in previous studies suggest high populations of weedy annual grasses such as yellow foxtail [Setaria pumila (Poir.)] may contribute to poor establishment of alfalfa under corn. In order to identify a threshold for initiating control of annual grasses, we evaluated summer ground cover, fall biomass, and fall plant density of interseeded alfalfa in response to varying populations of yellow foxtail. An increase in yellow foxtail density from 0 to 125 plants per square meter in June led to a sharp decline in alfalfa groundcover from 90% to 20% in August. This reduction in groundcover was associated with a post-establishment decline in shoot and root mass and a reduction in plant density of alfalfa from 250 to 146 plants per square meter in October. The results suggest that yellow foxtail populations in June should be kept below 50 plants per square meter to obtain fall alfalfa densities close to 200 plants per square meter in October that are recommended for maximizing alfalfa yield the following year. This research provides crucial information to guide control of annual grasses in this intercropping system.