The effects of spring tillage sequence on summer annual weed populations were evaluated over two cycles of a 3-year crop rotation of snap beans ( Phaseolus vulgaris), sweetcorn ( Zea mays), and winter wheat ( Triticum aestivum). Continuous no-till (N) planting of vegetable crops each spring (NNNN) reduced summer annual weed density by 63-86% compared with that of continuous conventional tillage (CCCC), depending upon the site and herbicide level. Hairy nightshade ( Solanum sarrachoides) populations were reduced by 88 to 96% when spring tillage was eliminated from the crop rotation. The effects of the NNNN spring tillage sequence on weed density were similar at two sites even though the crop rotations at the two sites began with different crops. The rotational tillage sequence of NCNC at the East site, in a crop rotation that began with maize, reduced summer annual weed density by 46-51% compared with that of continuous conventional tillage and planting (CCCC) at low and medium herbicide rates, respectively. In contrast, the tillage sequence of CNCN in the same crop rotation and at the same site increased weed density by 80% compared with that of CCCC at a low herbicide rate. The effects of the NCNC and CNCN rotational tillage sequences on weed density were reversed at the West site, and was probably caused by pairing sweetcorn with conventional tillage rather than no-tillage. The reduction in summer annual weed density caused by reduced spring tillage frequency did not significantly increase crop yields.
