Common name: Round-headed apple tree borer
Scientific name: Saperda candida
Hosts: The round-headed apple tree borer (Saperda candida) is a common pest on fruit trees, such as apple and pear. It has also become a pest on ornamental species, including hawthorn, mountain-ash, serviceberry, chokecherry and cotoneaster.
Newly transplanted trees and trees under stress are particularly susceptible. Healthy trees can often tolerate some damage from the borer.
The round-headed apple tree borer is native to much of eastern North America.
Damage
Round-headed apple tree borer adults will feed on leaves and fruit, but this damage is relatively minor. The real damage is done by the larvae, which tunnel under the bark into the sapwood. The larvae produce long tunnels. This damage can girdle a tree, leading to dieback of branches.
Areas where larvae are tunneling can often be identified by sap oozing out of the bark. Small, ¼-inch holes may be seen in the base of the tree. Sawdust-like excrement may also be seen at the base of the tree.
The borer can attack both weakened and healthy trees. In healthy trees, the larvae may be killed by a heavy flow of sap, and this can minimize damage.
Life Cycle
The round-headed apple tree borer takes two to three years to complete its life cycle. Because of this, the insect may be found overwintering in various larval stages in the sapwood and heartwood. Adults begin to emerge from the tree in late spring.
The adult borer is a narrow beetle about ½ to ¾ inches long, with a light brown body marked by two long white stripes.
Newly emerged beetles will feed and then mate. Each female can lay about 40 eggs.
The female makes a slit in the bark, near the base of the tree and inserts the egg between the bark and the sapwood.
The eggs hatch into cream-colored larvae. The larva has a very small black head, and behind the head is an obvious flattened segment, which gives this insect its common name.
The newly hatched larvae enter the bark near the areas where they hatched out of the egg. The larvae spend the season making long tunnels under the bark and feeding. They will spend two winters in the wood of the tree.
In the spring of the third year, the larva pupates in a chamber under the bark before emerging as an adult
Management
Cultural Management
Trees and shrubs of low vigor—or in a weakened state of health—are especially susceptible to borer attack.
Prevention is the key in controlling wood-boring insect pests.
Grow only trees and shrubs that are adapted to the area and site. Keep plants healthy and vigorous through proper planting, mulching, watering, fertilizing, pruning, and winter protection practices. Protect trees from injuries. Remove dead limbs or trees promptly to avoid infestations. Remove bark from felled trees if stored for firewood.
Biological Management
There are naturally occurring enemies of this native pest, primarily woodpeckers. They can help reduce borer populations, but will not always give complete protection.
Chemical Management
Systemic insecticides and trunk sprays are available to manage this pest.
The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.
For more information, contact The Morton Arboretum Plant Clinic at 630-719-2424 or plantclinic@mortonarb.org.