Corn, soybean, and weed responses to spring-seeded smother plants

Field and greenhouse research was conducted to better define the characteristics of a spring-seeded smother plant system for weed control in corn (Zea mays L.) and soybean (Glycine max [L.] Merr.). In the greenhouse, emergence and early growth of two medic (Medicago) species was greatest when planted 1.5 cm deep. In the field, Berseem clover (Trifolium alexandrinum L.), four medic species, and yellow mustard (Brassica hirta Moench) were planted immediately after corn or soybean planting in a 25-cm-wide band centered over the crop row. All species achieved 45% or more ground cover by 72 days after planting and yellow mustard often generated ground cover more quickly than other species. Weed suppression varied, with yellow mustard and Sava medic (Medicago scutellata L.) often providing greater weed suppression than other species. However, weed suppression was highly variable and crop yields were usually reduced compared with weed-free plots. Killing Sava medic 30 days after planting reduced weed suppression and did not increase corn yield compared with allowing the medic to survive until maturity. Delaying seeding of Sava medic until rotary hoeing increased weed suppression compared with rotary hoeing alone.