Birch: Bronze birch borer
Adult bronze birch borers are olive to bronze-colored beetles approximately 1/2″ long. They lay their eggs in bark cracks or under flaps of bark. The larvae bore into the branches or trunk after hatching and bore winding galleries along the cambial layer (between the wood and the bark). The larvae grow to about 1″ long and are creamy to white in color with a head wider than the body. The galleries may heal with swelling showing on the outside of the tree (lumpy bark), or may girdle and kill branches or trunks. Leaves may be yellow (chlorotic) as a result. The adults may feed on leaves, but cause little damage. Bronze birch borers attack trees weakened by age, environmental stresses, or previous insect attacks.
Use Integrated Pest Management (IPM) for successful plant problem management.
Select non-chemical management options as your first choice!
- Woodpeckers and parasites are important controls of bronze birch borers in rural areas.
- Keep trees healthy. Vigorous trees are much less susceptible to borer attack. Prune out dying branches.
- Prevent injury and insect damage.
- Plant resistant birch species and cultivars. Betula lenta, B. nigra, B. nigra ‘Heritage’, B. papyrifera, and B. papyrifera ‘Snowy Birch’ are resistant, while the species B. populifolia and the cultivars ‘Monarch’, ‘Whitespire’, and ‘Crimson Frost’ are moderately resistant.
IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.
- Apply materials to the trunk and lower limbs.
- Apply generally in late spring when adults are active.
- Three applications at 2-3 week intervals may be needed to cover the extended adult emergence period.
- Sevin (carbaryl) is particularly toxic to bees. Avoid carbaryl if there is any possibility of pesticide drifting onto nearby blooming plants.
- Homeowners should not make foliar applications to trees over 10 ft tall.
- Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.
Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.