The success of organic wheat ( Triticum aestivum L.) production can be severely inhibited by weed and disease pressures. This study sought to determine the effectiveness of wheat intercrop mixtures in suppressing weeds and diseases and increasing grain yield and net return. Field experiments were conducted on organically managed land in 2004 and 2005 and three representative intercrop systems were tested: wheat with other cereals [oats ( Avena sativa L.), barley ( Hordeum vulgare L.), and spring rye ( Secale cereale L.)]; wheat and noncereal seed crops (flax [ Linum usitatissimum L.], field pea [ Pisum sativum L.], oriental mustard [ Brassica juncea L.]); and wheat and cover crops (red clover [ Trifolium pratense L.], hairy vetch [ Vicia villosa L.], annual ryegrass [ Lolium multiflorum Lam.]). The cereal intercrop systems provided no consistent yield benefit over wheat monocultures. Results from noncereal-wheat intercrops were variable. Wheat-flax reduced the wheat crop to unacceptable levels but was capable of reducing wheat flag leaf disease levels. Wheat-field pea resulted in the lowest disease levels, yet had inconsistent yields, and more weeds than wheat monoculture. Wheat-mustard did not reduce weeds or diseases, but it was capable of high grain yields and net returns, though usually hampered by flea beetle ( Phyllotreta cruciferae) attack. The effect of cover crops on wheat was affected by environment. Wheat-red clover and wheat-hairy vetch did demonstrate the ability to maintain high wheat grain yield in certain site-years. In conclusion, wheat intercrop mixtures provided little short-term benefit over monoculture wheat in this study.
