One of my life rules is never to spray insecticides at a height above my waist. Pesticides can easily move off target with wind and can be carried into areas where they aren’t needed or wanted (like on the person spraying). This is where systemic insecticides comes in. Systemic Insecticides are mixed with water and poured around trees and shrubs, no spraying required. They work great and human exposure to insecticide is limited. The problem is that for a fifteen foot, multiple trunk Crepe Myrtle it takes several quarts. Stop by Wells Brothers and pick up a gallon of Ferti-lome Tree & Shrub Systemic Insect Drench . A gallon jug sells for $35.99.