| Pest Control : bronze birch borer |
Description The adult borer is olive green to black with metallic coloured reflections. The beetles are about 6 to 11 mm in length and are very slender in profile. The females are quite strong flyers. The adult beetles feed on leaves of birch and poplar trees. The larvae are cream coloured and about 35 mm at maturity. The larvae have a pair of spines at the posterior end. Larval galleries are from 75 mm to 125 mm in length. Damage The feeding activities of the borer larvae girdle tree trunks and limbs cutting off sap flow, resulting in their death. The larvae tunnel underneath the bark causing a ridge in the bark. The ridging may be apparent visually, but is more likely to be found by feeling along, the normally smooth, bark and noting a slight rise. The bark covering the raised area can be gently sliced away, revealing a serpentine trail of darkened material. The darkened material is excrement and can be flicked out of the trail with a knife. Emerging adults will chew a hole in the bark shaped like the letter "D". This distinctive "D" hole is about the same size as the "D"s on a typewritten document. Life Cycle The bronze birch borer has a two year life cycle. The adult borers emerge, and chew their way out of the tree bark in June. The adults lay eggs near the top of the birch tree. The eggs hatch and the new larvae chew their way into and underneath the bark. The larvae fed and grow working their way down the trunk. The larvae over winter and pupate in the spring. The pupa mature into adults and the cycle is repeated. As attacks are repeated the egg laying takes place on lower parts of the tree. Once a birch tree is infested by the bronze birch borer, control is very difficult and the chances for a cure are very slim. It is possible to remove dead or infested branches and trunks. Wood should be removed well below the last sign of a borer. The signs to look for are the ridging of the bark and the adult's "D" emergence holes. Trees with a great deal of dieback from the bronze birch borer should be removed. There are no regulations regarding the disposal of wood from infested trees, but as the larvae overwinter underneath the bark, firewood can serve as a source of infestation for other birch trees. A good neighbour would either dispose of the wood, or be sure to burn the resulting firewood before the next spring. |
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The bronze birch borer is an insect of increasing importance. It is the most important pest of ornamental birch trees, and to a lesser extent poplar trees. The insect targets old and stressed birch trees, boring underneath the bark and feeding off the sap conducting tissue. The borers start at the top of the birch tree and eat their way down. A sure sign of a bronze birch borer infestation is a leaveless dead tree top. Unfortunately, once a tree is infested with bronze birch borer, controls are largely unsuccessful. Complete death of the tree results. Prevention of infestation by maintaining tree health is the best course.
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