Answer: Once borers have infested a tree, they can be difficult to control. Insecticidal sprays can be successful only if they are applied to the tree when the adult borers are active and laying eggs. Consequently, the proper timing of insecticide sprays is critical for effective chemical control of borers.
Adults typically begin emerging in May and egg-laying can continue from June to September. Hence, larvae of varying sizes may be found throughout the summer. Adults are sun-loving insects and can be found in greatest numbers on the sunny sides of trees or logs. Eggs typically are deposited under bark scales or in bark crevices on the south and west sides of the main trunk and larger branches.
The larvae bore (tunnel) into the bark and feed on the phloem and outer sapwood. Tunnels in trees often can be 3 inches long or more. As the larva feeds, it fills the tunnel with a powdery frass. Mature larvae are white, about 1 inch long, and slender, except for a broad, flat enlargement of the thoracic segments behind the head (Figure 1). During the fall the larva will bore deeper into the wood, where it will spend the winter and pupate the following spring.
Applying carbaryl (Sevin), permethrin or any other appropriately labeled product to the trunk and larger limbs may provide some control.
Because adult emergence and egg-laying can occur over a long period of time, monthly insecticide applications may be needed over the course of the summer. Please read the label carefully before using any chemical for proper rates and application procedures.
Best wishes with your apple tree!
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