WINTER COVER CROPS AND VINEGAR AS WEED CONTROL TECHNIQUES IN SUSTAINABLE COTTON PRODUCTION

摘要

Weed abundance and diversity in cotton may be influenced by cover cropping, tillage regimes, and the use of non-synthetic organic herbicides. Organic cotton production was partially simulated in the Rio Grande Valley of South Texas. Black oat (Avena strigosa) and hairy vetch (Vicia villosa) winter cover crops were planted in plots. Six weeks after planting, pigweed (Palmer amaranth, Amaranthus palmeri), common purslane (Portulaca oleracea), and several members of the Asteraceae (sunflower family) were frequently-encountered winter weeds. Total weed cover was 17 to 24% higher in plots containing a cover crop than in tilled plots lacking cover, and purslane cover was 10% to 13% higher in cover crop plots, while pigweed cover was not affected. Seven weeks after planting cotton, total weed, pigweed and purslane cover did not differ between plots that had contained winter cover and plots without cover. In untilled cotton plots in separate fields maintained with conventional fertilizers and pesticides, weed cover was 18% greater than in tilled organic or conventional plots. Cotton plants grown conventionally, with or without tillage, were up to 3.4-fold taller than cotton plants in the organic field. To simulate organic chemical weed control, weeds andcotton were grown together in pots in a greenhouse and exposed to foliar applications of vinegar. Young (1.5 wk-old) pigweed, purslane, and sunflower (Helianthus annuus) were 100% controlled by vinegar containing 9.0% and 4.5% acetic acid, but 78% and 28% of 1.5 wk-old cotton seedlings were also killed by these doses, respectively. Vinegar solution containing 0.9% acid caused 48% or higher mortality in 1.5 wk-old weeds, while causing no mortality in cotton. Damaged cotton plants attained heights and leaf counts similar to undamaged controls within 2 weeks after application. Older weeds and cotton (3.5 and 5.5 wks old) did not show significant mortality to 0.9% acid vinegar. Weeds of these ages were partially controlled (up to 33% pigweed, 68% purslane,90% sunflower) by 9% acid vinegar. Only 10% of cotton plants of these ages were killed by 9% vinegar, but damaged plants had fewer leaves than control plants two weeks after application. In 1-m 2 field plots, 9% acid vinegar killed 26% of young, vegetative and 8% of mature, flowering pigweed plants, and 28% of young cotton plants. Winter cover crops do not control winter weeds as effectively as tillage, but could suppress winter and spring weed buildup under no-till conditions. Vinegar has limited utility for organic control of young weeds growing in cotton fields.