SAP-sucking lerps are thought to be behind a mysterious attack on a species of eucalypt in the Perth Hills.
The Shire of Mundaring said it has received numerous calls from concerned residents who fear the trees are dying.
Environmental officers believe that in most cases, the temporary leaf loss or ‘defoliation’ is caused by a naturally occurring and common insect, psyllids (also known as lerps).
Tree management supervisor Matt Bonsack said the psyllids attack the Flooded Gum (Eucalyptus rudis) species which can be found along water courses, on flood plains and around wetlands.
“These trees provide habitat for many insects, birds and mammals as well as help prevent erosion along creek lines and rivers,” he said.
“Unfortunately, this iconic tree can periodically look quite unhealthy – leaves can brown or die off, resulting in a thinning ‘twiggy’ looking canopy.
“Trees that are already stressed may have a reduced ability to cope with the infestation and this can have the potential to cause the death of a tree however this is uncommon and the vast majority of trees will recover.
“Infestations have been particularly noticeable this year in Greenmount, Helena Valley and Swan View.”
Mr Bonsack said trees can become stressed due to a range of factors including loss of understorey, grazing, soil erosion, salinity, reduced rainfall and fungal diseases.
“It’s important to remember that trees affected by psyllids are in a state of defoliation rather than being close to death and they should not be removed,” he said.
“You will be able to see the extent of damage caused by the insects by examining the leaves. However even if the tree is leafless, scratching of the bark should reveal green sapwood underneath.”
The Shire has previously investigated options for the treatment of psyllid infestations.
It is recommended that no intervention is made in most circumstances because the insect is naturally occurring and trees usually outgrow the damage caused.
An insecticide can be used for psyllid treatment but will also kill other beneficial insects such as bees and predatory insects.
Shire staff will continue to monitor the psyllid outbreak and would only use chemical intervention as a last resort.
Residents concerned about the health of Flooded Gums on their property are urged to adopt the following strategies:
Apply a good quality compost around trees to improve soil health and aeration, which can improve water penetration and root growth
Remove weeds and re-establish the understorey with native shrubs to improve soil health and attract insects and birds that predate on psyllids
Provide water to drought stressed trees in summer;
Remove stock to prevent soil compaction, which damage roots and reduce uptake of water and nutrients.