DESCRIPTION
Adults are an olive bronze beetle 13 mm long. They’re not often seen, but can be found during July and August in bark crevices in upper branches of birch trees. Whitish larvae can be up to 25 mm long with a blunt head. The first noticeable signs of the insect are small yellow leaves or dead branches in the upper part of birch trees.
DAMAGE
Larvae chew tunnels under the bark where the xylem and phloem meet, causing ‘girdling’ of the trunk or branch. Visible damage includes lumpy bark in upper branches or trunk as well as small sparse leaf development, yellow leaves and/or dead branches in upper portions of trees.
LIFE CYCLE
Larvae overwinter inside the branches and begin feeding again when sap starts to flow. Pupation also occurs inside the tree, with adults chewing a D-shaped hole in bark, emerging in June or July. Adults lay eggs in upper branches until the end of August. Upon hatching larvae bore directly into the tree. Borers may have a 1 or 2 year life cycle.
PESTICIDES
None recommended.
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No satisfactory control is known. Pruning infected branches 30 cm below any "lumpy bark" may prolong the tree's life, otherwise removal of the tree is inevitable. Burn all wood to destroy the larvae inside. The best control is prevention by keeping the tree adequately watered and fertilized. Borers can’t readily attack healthy trees. Heritage Birch (Betula nigra Heritage), a white barked birch, is resistant to bronze birch borer.