Interactions between cover crops and weed management in Iowa's conventional cropping systems

Abstract

The effect of different levels of cereal rye (Secale cereale L.) residue on common waterhemp (Amaranthus rudis Sauer) and common lambsquarters (Chenopodium album L.) emergence was determined. Cereal rye seeding date had a greater effect on rye biomass accumulation and percent cover than seeding rate. Common waterhemp emergence was equal to or increased in the presence of cereal rye residue in both 2013 and 2014 compared to the control. Common lambsquarters emergence was increased in two treatments in 2014 but was otherwise unaffected by cereal rye. The presence of cereal rye residue increased the time to 10% and 50% emergence of common waterhemp in both years but had less effect on common lambsquarters. The lack of weed emergence suppression seen in these experiments is a concern for cover crop use in Iowa’s conventional cropping systems, while the delay in weed emergence associated with cereal rye residue may be beneficial or detrimental to weed management. Greenhouse trials determined the soil activity of low rates of eleven corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] herbicides on five cover crops: cereal rye (Secale cereale L.), oat (Avena sativa L.), hairy vetch (Vicia villosa Roth), lentil (Lens culinaris Medik.), and radish (Raphanus sativus L.). Cereal rye was the most tolerant cover crop, whereas radish was the most sensitive species. Dry weight of radish was severely reduced by nearly all herbicides, whereas other cover crop species had smaller reductions due to herbicide injury. Root growth of oat was inhibited more by pendimethalin than the other species. Flumetsulam + clopyralid, atrazine, and herbicides containing isoxaflutole caused significant injury to most species studied.