Effect of hand defoliation on herbicide efficacy in honey mesquite

Greenhouse and field experiments were conducted to evaluate the effect of hand defoliation of honey mesquite (Prosopis glandulosa Torr) before herbicide application on herbicide efficacy. In the greenhouse, the monoethanolamine salt of clopyralid, the butoxyethyl ester of triclopyr, and 1:1 mixtures of clopyralid plus triclopyr were applied as foliar sprays at 140 g ha(-1) each on 2-year-old single-stemmed plants averaging 50 cm tall. In the field, the same. herbicides were applied as broadcast sprays at rates of 280 g h(-1) on multistemmed trees 1 to 2 m tall. Plants were defoliated prior to herbicide application at 0, 25, and 50% of original foliage. Defoliation at 25 or 50% did not reduce herbicide efficacy compared to nondefoliated plants in the greenhouse or field. The clopyralid:triclopyr mixture was sometimes synergistic in controlling honey mesquite in the greenhouse and field.