The yellowing of leaves on mesquite trees could be caused by improper watering, a nutrient imbalance, or pests and diseases. How much and how often do you water your mesquite tree? Check the soil - is it soggy? If you have over-watered it, then you need to refrain from watering it for a little bit. Have you been fertilizing your tree? Inspect the tree closely - does the tree have any signs of insect damage?
For more information on the care of mesquite trees, please visit the following link: