Don looked at a gum tree with marks all over the trunk, probably caused by the larvae of wood boring insects like longicorn or jewel beetles. They’re often found feeding in the phloem region just under the bark, and in severe cases they can ringbark a tree. Healthy trees are able to defend themselves by exuding kino or resin, but stressed trees may have already used up all their stored energy reserves, which makes them very susceptible to borer attack. In the case of the gum tree, Don stated his belief that the main cause of the stress was almost certainly lack of water. The tree would have been there before the houses, roads and footpaths were built. Sealing over a large part of the root zone with bitumen or concrete means water cannot penetrate easily, and this would be even more of a problem in times of drought. If a tree has been attacked by borers it could fall on houses, cars, or worst of all, people.
What to do:water trees during dry periods; a sprinkler to give a thorough soaking is best apply Seasol around the base of stressed trees to help them recover
Cost and availability:
Seasol is available at most nurseries and hardware stores. Prices are around $5.95 for 250ml, $9.95 for 500ml and $18.00 for 1 litre.
Australian Trees: Their Care and Repair (1988), by P. Hadlington and J. Johnston, is useful for identifying insects found on trees in Australia, and looks at other tree problems as well. It is published by University of NSW Press, Kensington.