Borers in Wattle

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Scientists are not sure how they do it, but insects like borers can single out a tree which is stressed and therefore weak, and attack that tree, leaving other healthy individuals around it alone. This is all part of the natural process and in a forest situation it is actually good, because weak trees are culled, leaving room for the stronger ones to develop. It’s not so good in a home garden situation where you may only have one tree in your backyard. Telltale signs that a tree has borers include sawdust on the ground or around the junction of branches, and holes disguised by webbing and frass. The tree will often exude resin or kino to try and fight off the attackers.

What are borers?

They are bark and wood feeding insects. Their larvae is usually found feeding in the phloem and in severe attacks they may ringbark the tree. Common borers include longicorn and jewel beetles, wood moths (for example xylorictid and cossid types) and termites.

Which trees are most susceptible?

Australian natives in particular acacia, eucalyptus and angophora are all prone to attacks by various bark and wood eating insects. Fruit trees such as peaches and cherry, and deciduous trees like birch and crepe myrtle are also prime targets for attack. Any tree which is stressed. A tree may be stressed for all sorts of reasons, eg. not enough water, lack of nutrients or a tree may be planted in the wrong situation or wrong climate. Producing a heavy crop, or responding to incorrect pruning and mechanical damage can also deplete a tree’s stored reserves, and lead to stress.

Treatments

Here are some of the old favourites:

plug the hole with a paste made from derris dust and dolomite stick a piece of wire down the hole to kill the larvae, then plug the hole with putty pour a few drops of kerosene or maldison down the hole then plug with putty use a tree borer kit

Don has tried all these treatments over the years without much success. So what to do?

You can minimise borer attack by choosing the right tree for the right situation, and make sure to water and fertilize your trees whenever necessary. Sometimes it is possible to use tree surgery to remove affected areas. Seasol, which is not a fertilizer but a growth promoter, is excellent for stressed trees. An easy and quick way to apply Seasol is to use an applicator which clicks straight onto your hose.

Further information:

Spray packs of Seasol are available from most nurseries and hardware stores. They cost around $13-$15.

Further reading

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.