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A troublesome pest for a birch tree is the Birch Leaf Miner (Fenusa pusilla) . Like the lethal bronze birch borer, it is the larvae of the birch leaf miner which causes damage by burrowing into birch leaves in search of nutrients. The first indications of birch miner infestation are small green spots on the leaf surface, usually noticeable in May or June, which develop into ugly brown splotches. A birch leaf miner infestation rarely kills birch trees on its own but it is disfiguring and can weaken a tree making it susceptible to borer attack.
Bronze birch borer
Of the number of pests which are attracted the birch trees, the bronze birch borer (Agrilus anxius) is the most important as it is both lethal and difficult to control. As an adult, the borer is a small bronze coloured beetle up to 2 inches (5cm) in length. The damage, though, is not caused by the beetle itself but by the larvae which bore into the phloem and cambium layers after emerging from their eggs on the bark. The borers' tunneling weakens and kills trees by interrupting the flow of sap. The entire lifecycle of the borer is one year from egg to beetle