Winter Cover Crops and Vinegar for Early-Season Weed Control in Sustainable Cotton

Abstract

ABSTRACT Weeds may be suppressed by winter cover crops and the use of organic herbicides such as vinegar. Black oat (Avena strigosa) and hairy vetch (Vicia villosa) winter cover crops were planted for 2 years as part of a sustainable production system for cotton in the Lower Rio Grande Valley of Texas, and were till-killed each spring prior to cotton planting. Palmer amaranth (Amaranthus palme ri), common purslane (Portulaca oleracea), and sunflower (Helianthus annuus) were frequently-encountered winter and spring weeds. Both cover crops controlled winter weeds as well as did winter tillage without cover. Black oats plots had 8% and 17% more total winter weed cover than no-cover and hairy vetch plots, respectively. Seven weeks after cotton planting, cotton cover was 10% to 15% less in former winter hairy vetch and no-cover sustainable plots than in former black oats plots, but cotton height did not vary by winter cover crop. Total spring weed, pigweed, and purslane cover did not vary between former hairy vetch, black oats, and no-cover plots. All sustainable plots had higher spring weed cover than did conventional plots maintained with cultivation and synthetic herbicides. Breakdowns in the sustainable spring weed management system (withholding of spring cultivation) or insect pest management system (failure of alfalfa strips) led to increases of 60% or more in weed cover in sustainable plots. Cotton lint yield (kg/ha) did not differ between sustainable and conventional weed management systems. When evaluated as a cover crop and weed management tool, vinegar containing 9% acid (1,550 L/ha) reduced live hairy vetch cover to less than 5% in one of two trials, but was not effective as a burndown herbicide on black oats. Vinegar at this concentration (2,980 L/ha) killed >80% of 30-day-old or younger cotton and sunflower and 10-day-old Palmer amaranth and purslane in field trials, but caused <50% mortality to mature Palmer amaranth and purslane. More dilute vinegar solutions (0.9% to 4.5% acid) caused little or no mortality. Black oats and hairy vetch covers controlled winter but not spring weeds in this production system. With more prolonged use, winter covers could become a key spring weed control component in sustainable cotton production. Vinegar could be useful in controlling young weed seedlings in non-crop areas, or as a follow-up to cultivation.