The effects of spring tillage sequence on summer annual weed populations were evaluated over two cycles of a 3-yr crop rotation of snap beans, sweet corn, and winter wheat. Continuous no-till (N) planting of vegetable crops each spring (NNNN) reduced summer annual weed density 63 to 86% compared to that of continuous conventional tillage (CCCC), depending upon site and herbicide level. Hairy nightshade 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 corn, reduced summer annual weed density by 46 to 51% compared to 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 to 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 sweet corn 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.
Nomenclature: Glyphosate; lactofen; metolachlor; barnyardgrass, Echinochloa crus-galli L. Beauv ECHCG; common lambsquarters, Chenopodium album L. CHEAL; hairy nightshade, Solanum sarrachoides Sendtner SOLSA; Powell amaranth, Amaranthus powellii S. Wats AMAPO; redroot pigweed, Amaranthus retroflexus L.; smooth pigweed, Amaranthus hybridus L.; snap beans, Phaseolus vulgaris L. ‘OR91G’; spring barley, Hordeum vulgare L. ‘Micah’; sweet corn Zea mays L. ‘Golden Jubilee’.
Additional index words: Conventional tillage, crop rotation, direct-seeding, no-till, rotational tillage, seedbank, seedling recruitment, weed density.
Abbreviations: H, high; HL, herbicide level; L, low; M, medium; TS, tillage sequence; WAP, weeks after planting.