Pacific flatheaded borer
Chrysobothris mali
36 host plants
Last updated
You will find reddish-bronze beetles, one-quarter to one-half inch long, on sun-exposed bark of stressed stone fruit trees in May and June. Larvae tunnel beneath bark leaving flat galleries that may girdle branches and trunks. Exit holes and sawdust accumulation appear on affected areas. Young trees and drought-stressed specimens are highly vulnerable. This is a significant pest of orchard and landscape Prunus species.
Plant healthy stock and maintain vigorous growth through proper irrigation and care. Reduce sun-exposure injury on newly planted trees using shade cloth. Remove heavily infested branches below the damage line. Apply preventive sprays in May through July when adult beetles are laying eggs.
Quick Reference
The Pacific flatheaded borer typically attacks weakened, injured, or stressed trees. The larvae feed between the bark and the sapwood. They can weaken and girdle trees. Injured bark may show dark depressions on the surface or cracks through which the sawdust-like frass can be seen. The larvae are white or cream-colored with broad, flattened heads. They can reach up to 1" in length. The adult borer is a dark, coppery-brown beetle. The broad, flattish adults are about 1⁄4" to 1⁄2" long. Adult females lay eggs in bark crevices on the trunk below the lowest branches. The larvae burrow into the bar
Cultural Controls
- Birds peck the larvae from under the bark with their beaks.
- Some parasitic wasps attack the borer.
- Carpenter ants eat both larvae and pupae from the wood.
- Beetles are attracted to weakened, sunburned, or injured parts of trunks and lay eggs in cracks on bark exposed to the sun.
- Protect young, newly planted trees from sunburn by whitewashing with an interior white latex paint.
- Paper trunk protectors or boards also may be used to shield the trunks...