Mesquite Seed and Seedling Response to 2,4-D and 2,4,5-T

Seeds ad seedlings of mesquite, Prosopis juliflora var. velutina (Woot.) Sarg., were cultured for 72 hours in aqueous solutions of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) at concentrations of 1, 2, 5, 10 and 50 p.p.m. Suppression was measured and expressed in root and hypocotyl growth, and total fresh weight, in comparison with controls. 2. Seeds and young seedlings of mesquite were found to be responsive to 2,4-D and 2,4,5-T but not so sensitive as some other plants. Concentrations above some other plants. Concentrations above 1 p.p.m show 2,4,5-T to be more toxic to mesquite than is 2,4-D. This has also been found true of foliage sprays applied to mature trees. 3. Suppression of both seeds and seedlings by 1 p.p.m of either herbicide shows the sensitivity of young plants to these compounds. Applications of much higher concentrations to mature plants as foliage sprays have not resulted in kills, indicating either lack of absorption and translocation or greater resistance of mature plants to these compounds.