Evaluation of Integrated Weed Control Practices in Conservation Agriculture Legume Row Crops

Abstract

Peanut (Arachis hypogaea L.) and soybean (Glycine max [L.] Merrell) are vital legume crops facing significant yield losses from weed competition, exacerbated by the rise of herbicide-resistant weeds like Palmer amaranth (Amaranthus palmeri). Conservation tillage systems, while beneficial for soil health, increase reliance on herbicides. This thesis focuses on investigating integrated weed management strategies combining cover crops and reduced tillage with herbicide programs in Alabama. Two field studies were conducted. The first evaluated strip-tilled peanut following cover crops (cereal rye - Secale cereale, wheat - Triticum aestivum, radish - Raphanus sativus, mixture) or fallow (disk-tilled, no-till) combined with four herbicide applications (PRE, POST, PRE+POST, NT) across all temporal and spatial replication. The second study assessed sweep tillage frequencies (single, double, triple pass) following a rolled-crimped cereal rye (Secale cereale) cover crop compared to a PRE+POST herbicide program and winter fallow (NT) in soybean across two locations. Weed biomass, density, visual control, and crop yield were measured. In the peanut study, rye, radish, and the mixture produced substantial biomass (>6000 kg ha⁻¹), providing early season weed suppression. PRE herbicides reduced early weed biomass by approximately 70% compared to NT plots (192 vs 651 kg ha⁻¹). Untimely radish termination led to volunteer radish issues without PRE herbicides. Late-season weed control relied heavily on herbicides; the PRE+POST program significantly reduced weed biomass (e.g., 742 kg ha⁻¹ vs >1300 kg ha⁻¹ for PRE/POST alone at one site) and provided the highest peanut yields (up to 3820 kg ha⁻¹), significantly outperforming NT checks (1333-1640 kg ha⁻¹). In the soybean study, cereal rye (Secale cereale) produced ~6000 kg ha⁻¹ biomass. The PRE+POST herbicide program consistently provided the best weed control (e.g., 79% visual control at 11 WAP) and the highest relative soybean yield (104% at the high weed pressure site, EVS). Sweep tillage efficacy varied; triple sweep provided intermediate control (60% visual rating, 1807 kg ha⁻¹ biomass at EVS 11 WAP), while single sweep often resulted in high late season weed biomass (5956 kg ha⁻¹ at EVS 11 WAP) and density, sometimes exceeding winter fallow. These studies demonstrate that integrating high-biomass cover crops, particularly cereal rye (Secale cereale), with robust, multi-mode-of-action herbicide programs (PRE+POST) enhances weed control and maximizes yield in peanut and soybean conservation systems. While cover crops provide valuable early suppression, their effect diminishes and sweep tillage efficacy is limited and context-dependent, generally not replacing effective herbicide programs, especially under high weed pressure situations.