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Tree insect infestations

Every year, Council managed trees risk seasonal insect infestations. In most cases, infestations are harmless to people and pets and cause little harm to the tree. Late summer is notorious for early signs of disease and pests, and Council will only address seasonal infestations in the most extreme cases. Tree health is usually unaffected, and the insect population will disappear in the cooler months.

Lerps (Psyllids)

Psyllids are Australian native, sap sucking insects that usually attack the Wallangarra White Gum (Eucalyptus Scoparia). They can also infest commonly planted and naturally occurring native tree species, particularly during hot and dry conditions.

The Psyllid populations usually explode every 4-5 years. Generally, a tree will withstand a Psyllid infestation though it may decline if it is already under stress.

Control options of Psyllids are limited, especially in urban areas.

Psyllids have several natural predators that keep their numbers in check, including spider mites, lady beetles and Rosellas.

Psyllid infestations cause:

  • the trees to temporarily lose their leaves,
  • discolouration of leaves – brown/red mottled appearance
  • white spots on the leaves, and
  • a non-toxic, sap like substance called Honeydew appears on the leaves.

Psyllids suck sap from the leaves of the trees and form a waxy layer over themselves called a Lerp. This waxy layer protects them from natural predators and the harsh Australian climate. This process is responsible for the clear, sticky substance all over and dropping from the leaves. Populations of Psyllids eventually collapse; once this happens, natural predators increase and essentially finish them off. Most trees recover reasonably well.

You can find more information in the NSW Department of Primary Industries.

eco organic garden
Credit: Eco organic garden

Elm Leaf Beetle

The Elm Leaf Beetle is a significant pest affecting elm trees during summer. Severe infestations of Elm Leaf Beetle can cause trees to lose their leaves and seriously weaken and leave them prone to other pests and diseases. If left untreated, Elm Leaf Beetle can rapidly defoliate a tree, particularly in warmer weather, and several years of infestation can cause tree death.

Elm Leaf Beetle larvae are tiny and initially black. Adults are yellowish-olive green in colour with two black stripes and are evident in spring. 

During spring, tiny eggs are laid in clumps on the underside of leaves. Larvae can be visible in the soil below the tree as they travel down the tree trunk to pupate, emerging as beetles after 1-2 weeks. 

Elm Leaf Beetles create a series of small holes in the leaves and destroy all but the leaf veins, creating a skeleton effect. Trees affected by Elm Leaf Beetle can lose their leaves by mid-summer, meaning there is no summer shade or autumn colours, reducing their ability to reserve energy over winter.

Total eradication of the Elm Leaf Beetle is challenging. The primary goal is to maintain Elm Leaf Beetle numbers (and damage) to an acceptable level. We have a two-year treatment regime for Council managed Elm trees to minimise damage to the tree.

Elm Leaf Beetle
Credit: Arborcraft

Plague Soldier Beetle

The Plague Soldier Beetles are native to Australia and are most common in spring and early summer when there is an increase in rainfall and humidity. Plague Soldier Beetles are harmless, and there is nothing to do but wait for them to disperse.

The beetles often swarm in large, localised groups around the blossoms of native trees, fruit trees, vegetable plants and other garden plants in such numbers that they can weigh down weaker plants. While this may be distressing to gardeners, the plants do not suffer much. The beetles are more interested in sucking nectar from the flowers and mating to bother eating the plants.

Plague Soldier Beetle
Credit: Museums Victoria

Spitfire Sawfly

The Spitfire Sawfly is part of the same insect group as bees, wasps, and ants found in Australia. The Sawfly gets its name from the saw-like ovipositor (a tubular organ) of the female, used to drill holes into the Eucalyptus tree leaves to lay her eggs. 

The larvae vary from dark blue or black to yellow and brown, depending on the species. The body is sparsely covered with white, bristly hairs. The adult wasps are mainly black or brown, with yellowish markings. While closely related to wasps, sawflies lack the narrow waists and stings of wasps.

When threatened, the larvae raise their heads and eject a strong-smelling yellow-green liquid predominantly of eucalyptus oil to deter predators. This action gives them their common name of spitfires.

Although adult sawflies usually remain hidden, the larvae are quite noticeable as they grow larger, resembling hairy caterpillars. During the day, the larvae congregate in clusters on the Eucalyptus tree branches for protection and disperse to eat the leaves at night.

Spitfire larvae feed on the leaves of young trees and regrowth stems and can strip the branches of leaves, particularly at the tops. This is usually replaced during the spring-summer flush of leaf growth. Severe retardation of high growth may result from repeated attacks, though the tree's death from Spitfires is unusual. There are several parasitic wasps that also naturally control the Spitfires.

Spitfire Sawfly
Credit: Project Noah

You can Report a tree issue if you are concerned about the health of a street tree and we will conduct an inspection and undertake work if necessary.

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