When adults emerge, the leaf covering drops out to create the shotgun effect and the leaves prematurely drop. Spray with a systemic insecticide to correct the problem. Suspect flatheaded borers if you find small, egg-shaped holes on the branches and trunk. Peek under the bark. If you find galleries packed with sawdust, you have borers.
Borers attack weak, run-down trees and shrubs.
Therefore, a vigorously growing plant is the best control. Paint the exposed trunks with a white, water-based latex paint to deter the insect. Olive trees begin shedding pollen this month. Prevent fruit set by spraying trees with Florel when blossoms first open and repeat as needed to abort the flowers. Also, drench blossoms with a jet of water each morning to prevent pollen from flying.