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All the leaves are brown…

June 26, 2017

And the sky is grey – are the starting lyrics of the Mamas and the Papas hit, California Dreamin and are certainly apt descriptors of conditions so far this winter in the King Parrot Creek valley. However it is not just the deciduous trees sporting brown leaves. Unusually, the leaves of a lot of eucalypts are brown too, particularly those of the River Red Gums (Eucalyptus camaldulensis).

A close look at the gum leaves will reveal that they are covered in off-white scallop-like structures. These are called lace or basket lerps (Cardiaspina sp.), shown below left in close up. They are the sugar-rich secretions from the nymphs of insects known as psyllids. Psyllids and their nymphs are sap sucking insects. They suck sap from eucalypt leaves to extract the protein on which they live. The remaining sugary waste is eliminated from their body and forms a protective cover under which the nymph lives. If you look closely at the photo (below right) you can just make out the form of the brown psyllid nymph under the lerp. There are many different types of psyllids and therefore lerp structures. Other lerps may take the form of sugar cones or even fairy floss.

In normal circumstances the nymphs cause a red/purple discoloration of the leaf (see picture right) and/or dead brown patches. However severe infestations of nymphs, as we are seeing in the valley this season, can result in severe browning of the foliage, defoliation of trees and sometimes dieback. It rarely results in the death of the tree. Natural predators of the psyllids, which include other insects and birds such as Pardalotes and Bell Miners obviously cannot control the sheer number of psyllids this season.

The common misconception is that the brown foliage is not due to psyllids but to water stress in the gum tree. If you hear that said, tell them they’re dreaming – Flowerdale Dreamin.

One Comment leave one →
  1. Peter Mitchell permalink
    June 26, 2017 9:12 am

    Hello Ron,
    One comment and one correction to this article. Psyllids and lerps and dead segments of leaves (or whole leaves) are having a big impact on the River Red Gums around Broadford (this year) and Seymour (last year). And with the damp weather, the lerps are being infested with black fungi,

    Bell Miners are part of the issue in some areas (we don’t see or hear them in our drier side of the hill country). Bell miners eat the lerps for the sugar but they leave the insects underneath – they are effectively farming the insects and harvesting the product (sugary lerps). They are also aggressive farmers and chase away other birds – notably the pardalotes and other leaf-gleaners that eat the insects as well. As a result, you sometimes come across patches of sick forest ringing wih the sounds of bell miners.

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