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Leaf Attack

September 12, 2022

Many folk have noted the large number of gum trees with significant die-back characterised by brown or missing leaves around the district at the moment. In the main this damage is caused by lerps, a parasite on eucalypt leaves that Ron Litjens has often written about with graphic photos and explanations on this blog.

Typical tree suffering dieback
Lerps on a eucalypt leaf and the damage they cause

People ask, will the trees recover? And the answer usually given is that this is a natural cycle and predators will increase to counter the abundance of lerps. However, we have created widespread landscape alteration and the natural predators of leaf-eaters may not be in sufficient abundance. In the 1980’s thousands of mature majestic eucalypts perished from dieback in New England, NSW, and the immediate cause identified was an abundance of Christmas Beetles, but the deeper cause was the continual attack on landscape integrity with removal of understorey plants, superphosphate-fed pastures and absence of habitat for the natural predators. This is a grim warning that they don’t always recover.

It is fascinating to note that the lerps are very selective: River Red Gums (E. camaldulensis) are badly inundated but right beside them will be a stand of Grey Box (E. microcarpa) with no lerps at all.

Another cause of defoliation is that this is an incredible year for Spitfires. I was sent a video of an inundation in a home garden of which this is an extract. These larvae of Sawflies (Perga spp) can defoliate a tree in short time, and in this garden, there were huge mounds and armies of them on trees, grass, fenceposts, in nightmarish numbers, worthy of a Hitchcock horror movie.

What can be done about them? There are natural predators – some hardy birds eat them, some stink bugs suck them, some beetles eat the pupae, some wasps parasitise them, but it takes a while for any balance to be restored. Trees usually recover but it may take a year or two.

Or we could leave home and live in a concrete high-rise in the city where nature will not be able to impact us!!

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