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Birch tree appears to be dying

birch tree dyingThe most threatening of the birch tree pests is the bronze birch borer (Agrilus anxius). As an adult, the borer is a small bronze coloured beetle up to 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. Evidence of borer infestation is a progressive thinning of the crown of the tree beginning at the top.  Trees generally die after about two or three years, that is, after two or three infestations by the larvae. 

What you can do

To help control the bronze birch borer there are several steps which should be undertaken: Prune out and destroy all dead or dying branches. If caught early enough, there are insecticides available to prevent new infestations of the borer. Trees with advanced crown loss will not benefit from insecticide use and should be removed. The good news is that healthy, well-situated, well-maintained birches are more resistant to the borer.

Females prefer to lay eggs in the sunlight and are less attracted to trees whose trunks are shaded. The insects are also attracted to tree wounds and so care should be taken to avoid damaging the bark of trees. Finally, trees under stress are more likely to be successful borer targets so it is important to ensure that birch trees receive adequate water and proper fertilization.

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