Spring-Seeded Smother Plants for Weed
Control in Corn and Other Annual Crops
Robert L. De Haan, Donald L. Wyse, Nancy J. Ehlke, Bruce D. Maxwell, and Daniel H. Putnam
Corn producers in developed countries rely heavily on herbicides and mechanical tillage to control weeds. Both herbicides and tillage, however, can cause undesirable environmental effects. Herbicides have been detected in surface water and groundwater at concentrations that exceed the lifetime health advisory limit for drinking water as established by the Environmental Protection Agency ( Goolsby et al. 1991; Klaseus et al. 1988). Mechanical tillage breaks down soil structure and decreases the amount of plant residue on the soil surface, which increases the risk of soil erosion ( Laflen et al. 1980; Langdale et al. 1991). Soil erosion causes on-site and off-site environmental degradation and poses a threat to long-term crop production ( Larson et al. 1983).
Cover crops or smother crops have been proposed as an alternative weed control method in corn ( Liebman 1988; Palada et al. 1983; Worsham 1991). Cover crops that suppress weeds could reduce herbicide and tillage inputs ( Palada et al. 1983), increase soil water infiltration ( Bruce et al. 1992), contribute nitrogen to the main crop ( Corak et al. 1991; Decker et al. 1994; Maskina et al. 1993), and reduce economic risk ( Hanson et al. 1993).
Research investigating biological weed control through plant interference has focused on the use of winter annual or perennial species sown in the fall and suppressed or killed with a herbicide in the spring ( Curran et al. 1994; Eadie et al. 1992; Eberlein et al. 1992; Echtenkamp and Moomaw 1989; Enache and Ilnicki 1990; Fischer and Burrill 1993; Grubinger and Minotti 1990; Hoffman et al. 1993; Johnson et al. 1993; Kumwenda et al. 1993; Mohler 1991; Teasdale 1993; Tollenaar et al. 1993). Species that have been evaluated as cover crops include alfalfa (Medicago sativa L.), Austrian winter pea (Pisum sativum L. subsp. sativum var. arvense (L.) Poir), barley (Hordeum vulgare L.), chewings fescue (Festuca rubra L.), crimson clover (Trifolium incornatum L.), hairy vetch (Vicia villosa Roth), ladino clover (Tri-