Efficacy and Crop Safety of Reduced dose Herbicide Mixtures for Weed Management in Alfalfa (Medicago sativa L.)

A major perennial legume throughout the world, alfalfa (Medicago sativa) is becoming more popular in Africa, where sustainable production depends on effective weed management. The most popular approach is chemical weed control, which mostly uses the herbicide imazethapyr. However, depending solely on one herbicide may result in inconsistent weed control in the field and cause environmental issues due to the use of greater pesticide concentrations. To address this issue, a two-year (2024 and 2025) field study was carried out to reduce the use of herbicides and find eco-friendly ways to manage weeds using herbicide combinations in Navrongo, Ghana during the rainy season. Imazapic, prometryn, imazethapyr, and 2,4-DB were shown to be safe and efficient in managing broadleaf weeds during the initial screening. Each broadleaf herbicide was combined with haloxyfop-R-methyl to increase the control spectrum and reduce the overall herbicide dosage. Haloxyfop-R-methyl + imazethapyr (36.5 + 56.5 g a. i. ha-1) effectively reduced herbicide input by at least 25% of the acceptable dose while providing broad spectrum weed control without impairing alfalfa performance. Furthermore, the combination of 2,4-DB (36.5 + 506.5 g a. i. ha-1) and haloxyfop-R-methyl produced excellent broad-spectrum weed control, enhanced alfalfa yield, and reduced total herbicide input by almost 25% of the prescribed dose. Imazethapyr controlled all the broadleaf weeds (Biden pilosa and Amaranthus spinosus L.) and grass weeds (>98%) effectively. Haloxyfop-R-methyl + imazethapyr exhibited a mixed dose response; a higher application dose resulted in to a drop in plant height and an increase in fresh and dry weight. The leaf area was 10% greater, the crop biomass at 36.5 + 56.5 g a. i. ha-1 was not substantially different from the weed-free control, and the weed control was more than 98% for both grass and broadleaf weeds. The mixture of haloxyfop-R-methyl + 2,4-DB at a dosage of 36.5 + 506.5 enhanced the leaf area by 8% while the crop's fresh and dry weights were approximately equivalent to those in the weed-free control. These combinations provide a crucial alternative for managing broadleaf weeds and reduce the need for frequent imazethapyr treatments. Therefore, these herbicide mixes provide safe, effective, and sustainable ways to manage weeds in alfalfa production.