Production management strategies that incorporate smother crops for weed and erosion control must be researched and developed to build a sustainable agricultural industry. Smother crops may also reduce herbicide and fertilizer applications. Alternative management systems will only be adopted by producers if crop productivity can be maintained, fit within current managements practices (or management that is considered feasible by the producers), control weeds or have other beneficial aspects, and are cost effective. Annual Medicago species (medics) have some traits such as vigorous seedling growth and short life cycles that may allow them to be utilized for weed management in row crops. The purpose of the research was to investigate if annual medics, when used as a spring-seeded living smother, crop would control weeds, not adversely effect com (Zea mays L.) productivity, provide organic material to soil, and be similar in cost to synthetic chemical application. Three species of annual medics Medicago truncatula Gaerth., cul ti var 'Caliph' (barrel medic); Medicago polymorpha L., cultivar 'Santiago' (burr medic); and Medicago scutellata L., cultivar 'Sava' (snail medic); were evaluated in field, laboratory, and greenhouse studies at two sites during 1995-1998. In 1995 and 1996 annual medics were planted at two planting dates (about two weeks prior to average planting date for the area and at corn planting) and at two broadcast planting rates (17 kg ha- 1 and 34 kg ha-') at sites located in Brookings, SD and Sioux Center, IA. Herbicides were not applied to medic treatments and N was applied at recommended rates. The 1995 growing season was cool and wet and medic grew aggressively in well-drained sites while the 1996 growing season was warmer and drier and medic biomass was about 70% less than in 1995. Medic planted early had more biomass and ground cover than medic planted at the same time as corn, and all medic senesced by early August. Medic reduced yellow and green foxtail (Setaria glauca (L.) Beauv. and S. virdis (L.) Beauv.), common lambsquarters (Chenopodium album L.) in 1995 and 1996. Medic reduced corn yield in 1995 and 1996. In 1996, the barrel medic broadcast at high rates reduced corn yield by about 30% compared to the weed-free control. During 1996-1998 at Sioux Center, medic was banded in the row and inter-row at a rate of 20.0 kg ha- 1 in the band. Corn yield was similar in the medic banded areas to yield when only herbicide was applied. Use of enterprise budgets indicate that the medic and non medic treatments had similar profitability. Leaf extract from three medics inhibited germination of green foxtail and velvetleaf (Abutilon theophrasti L.) seeds, and generally did not inhibit com seed germination. Allelopathic effect of medic on corn growth was not observed when both were grown together for six weeks in a greenhouse study. The information gained from this research indicates that annual medics may have a very important niche in achieving more sustainable, environmentally benign crop production systems. Planting medic as a smother crop may be very appropriate on environmentally sensitive land.