Organic producers are seeking alternative tactics for weed control so that they can reduce their need for tillage. In this study, we examined cover crop strategies for suppressing weed growth after harvest of wheat. Three cover crop treatments, red clover (mammoth type), a mixture of oat and dry pea, and a control were compared. Treatments were established in both winter and spring wheat, resulting in six treatments arranged in a randomized complete block design. Red clover was underseeded in wheat by drilling in the spring, and the oat/pea mixture was planted in August. Oat was planted uniformly across all treatments in the following growing season. The red clover treatment effectively suppressed weeds, reducing post-harvest weed biomass, density of volunteer winter wheat, and seed production of downy brome by more than 99% compared with the control. Oat/pea was not effective for weed management, likely because of less fall growth and competition compared with red clover. Underseeding red clover did not affect winter wheat yield, but reduced spring wheat yield by 17%. Oat yield, however, was reduced by volunteer crop plants and downy brome infestations in all treatments. Underseeding clovers in winter wheat may effectively manage weeds and, if they winterkill, can replace the need for tillage to control weeds after wheat harvest.

Organic producers are seeking alternative tactics for weed control, so that they can reduce their need for tillage. In this study, we examined cultural strategies for controlling weeds during the transition from a cool-season crop to soybean. The study was arranged as a two-way factorial, with factors being choice of cool-season crop and tillage treatments. The cool-season crops were either spring wheat harvested for grain or an oat–pea mixture harvested for forage. Five tillage treatments, ranging from intensive tillage to no-till, were established following each cool-season crop. Two tillage treatments included the cover crops, oat plus oilseed radish. Soybean was planted the following growing season. Each soybean plot was split into two subplots: weed-free and weed-infested. A cultural system comprising oat/pea as a preceding crop with no-till and cover crops reduced weed biomass in soybean 63% compared to intensive tillage. Reduced weed biomass resulted because of delayed weed emergence and lower weed community density. Consequently, soybean yielded 14% more in this treatment than with the intensive tillage treatment when weeds were present. Weed community composition also differed between the two systems; horseweed and field dandelion were prominent in no-till, whereas common lambsquarters, redroot pigweed and buffalobur were prevalent in the tillage control. Other treatments did not control weeds better than intensive tillage. A cultural system approach may minimize the need for tillage during the interval between cool-season crops and soybean.