Elm Leaf Beetle
Elm Leaf Beetles become active from October and create a series of small holes in leaves during the summer months.
The Elm Leaf Beetle (Xanthogaleruca luteola) was first discovered in rural Victoria in 1989 and quickly spread to the inner city suburbs of Melbourne.
Elm Leaf Beetle was first detected in South Australia sometime in 2011. However, it was not declared a pest at that time under the Plant Health Act (SA). This meant that it was not a notifiable pest and Biosecurity SA did not treat or apply specific measures to control the beetle.
We are now observing the consequences of its presence in South Australia with wide spread infestations on our states ‘Elm Trees’.
Life Cycle & Identification
Adult beetles are known to become active in October and are then present through until April the following year.
They are evidenced by a ‘shot hole’ appearance in leaves. They have the ability to travel through flight (fly) or ‘hitch a ride’ on vehicles, humans, etc. They move from tree to tree feeding and laying eggs on the underside of leaves.
Beetle larvae then destroy all but the veins of the leaves, creating a ‘skeleton’ effect. This damage destroys the trees ability to achieve photosynthesis, produce and store energy, maintain growth, vigour and active defence mechanisms.
There may be up to three life cycles of the beetle in a single season, depending upon weather conditions.
In terms of control, there are a number of options available to address Elm Leaf Beetle:
This method involves the use of injectors which are introduced to the vascular system of the tree by means of a small drill hole.
The advantage of the injection method is that the application method is target specific and as such is very effective. It is also considered to be the safest method of control.
This method is used by the City of Norwood Payneham & St Peters when treating and protecting the Elm Trees throughout the urban forest.
This method involves injecting the soil under the drip line of the tree using an appropriate insecticide.
The chemical is taken by the feeder roots and translocated through the tree’s vascular system to the shoots and leaves where it will kill the adult beetle and also the larvae when they start to feed.
As the movement of the chemical within the tree is relatively slow, soil injections need to be carried out at least six to eight weeks prior to emergence of the beetles from hibernation.
This method of control kills the Elm Leaf Beetle once the chemical has been absorbed by the tree. However, it may destroy good micro-organism located within the soil profile.
Similar to the soil injection method, whereby a chemical is applied to the ground in a tablet form which can be supplied with a slow release fertiliser or initiator.
Similar to the soil injection, this method destroys the Elm Leaf Beetle once the chemical has beenabsorbed by the tree. However, it may also destroy good micro-organism located in the soil.
Banding can be undertaken by applying gel or sticky tape (stick facing outwards) to the trunk of the tree and the pest sticks to the gel when climbing up or down the trunk.
Applications need to be done monthly when there are mature elm leaf beetle larvae, from around November through to January. In wet weather conditions, you will need to reapply. In addition to that, Elm bark is deeply furrowed thereby making effectiveness very difficult to predict.
This method uses Carbaryl (1-naphthyl methylcarbamate) which is an insecticide used to control pests in home gardens, on ornamentals, lawns, fruit and vegetables and around public buildings. It is also used in the control of insects on domestic animals.
The chemical is sprayed on the leaves and is a contact insecticide. It may kill whatever comes in contact with the chemical. However, it is non-specific and as Elm bark is deeply furrowed the effectiveness is difficult to predict. In addition to that, the chemical is only registered in Victoria and Tasmania for use.
This method is very similar to stem spraying / banding and also uses Carbaryl.
Again, the chemical is sprayed on the leaves and is a contact insecticide. It may kill whatever comes in contact with the chemical. However, it is non-specific and as Elm bark is deeply furrowed the effectiveness is difficult to predict.
The Council has approximately 335 Elm Trees planted throughout the City.
Of those, 233 are Chinese Elms which have a high resistance to Elm Leaf Beetle. The remaining 102 Elms are a mixture of English, Dutch and Golden Elms which are susceptible to Elm Leaf Beetle. These trees are located throughout the City.
The Council has treated its 102 Elms which are considered susceptible to this pest in order to protect these trees against this pest.
It was determined the most appropriate treatment for the Council’s 102 Elms was stem injection and this was carried out on all Council’s English, Dutch and Golden Elms.
Council staff will now monitor these trees closely to ascertain the effectiveness of the treatment and whether further treatment may be required.
Your elm trees
For a list of qualified arborists, you can visit the South Australian Society of Arboriculture (SASA) website and download the SASA Members list.
Please note, the Council doesn’t recommend any particular arborist or pest controller.
If you require further information, regarding the Council’s actions to treat street trees against this pest, please contact Councils arborist on 08 8366 4588.