Weed Seed Population Dynamics During Six Years of Weed Management Systems in Crop Rotations on Irrigated Soil

The influence of two weed management systems was determined on weed seed and seedling populations and on yields of cantaloupe ( Cucumis melo L. var. reticulatus Naudin ‘Perlita′), bell pepper ( Capsicum annuum L. var. grossum ‘Grande Rio 66′), cotton ( Gossypium hirsutum L. ‘CP 3374′), onion ( Allium cepa L. ‘1015Y′), and cabbage ( Brassica oleracea , var. capitata L. 'Sanibel′) sequentially grown in two 3-yr cycles. Palmer amaranth ( Amaranthus palmeri S. Wats. # AMAPA) did not exist initially, but hurricane-introduced seed populations increased to 1.1 billion/ha as seed populations of common purslane ( Portulaca oleracea L. # POROL) decreased from 786 million/ha to 124 million/ha in the 6-yr period, without weeding or herbicide. Use of herbicides and handweeding reduced Palmer amaranth seed populations 98%, but 18 million/ha still remained after 6 yr. The use of herbicides and Palmer amaranth interference decreased the seed populations of common purslane by 84%, but handweeding was inefficient. Yields of all but the first crop of cantalouple were almost totally eliminated by season-long interference of Palmer amaranth. Savings with the utilization of herbicides rather than handweeding ranged from $62/ha for cotton to $4703/ha for bell pepper.