The Elm Leaf Beetle (Xanthogaleruca luteola) was first discovered in Victoria in 1989 and has since been detected in South Australia from 2009. Initially, it was not a declared pest under the Plant Health Act (SA) and therefore there were no specific measures in place to control the beetle.
There are now wide spread infestations throughout our Elm Trees in South Australia.
The majority of Elms planted in our streets, parks and gardens are European species and are susceptible to attack. The Asian species such as the Chinese Elm are relatively resistant to attack.
An infestation of Elm Leaf Beetle will result in severe defoliation. The infested trees will produce new foliage; however it is likely to be smaller and sometimes distorted. Elms that suffer from repeat attack will become weak and this greatly reduces their aesthetic and amenity value. Trees will also be more likely to succumb to other pests and diseases.
Elm Leaf Beetle Life Cycle
In order to control the insect, it is important to have an understanding of the elm leaf beetle’s life cycle.
September –The adult beetles begin emerging from shelter. If there is insufficient foliage on the trees, they will die.
October-Most adult beetles will emerge and fly to Elm trees to feed on new foliage. The beetle is not easily seen but their presence will be evidenced by shot hole damage on the leaves.
November-The beetles will mate and lay egg clusters on the Elm leaves. The eggs look like a small double row of lemons. The eggs will take 7-10 days to hatch.
December-The larvae begin to hatch. They feed on and skeletonise the foliage on the Elms. They will grow from one to ten millimetres in length and then move down the branches and trunk to pupate.
The Elm Leaf beetle pupae are usually five millimetres in length and are a bright yellow in colour. They will be found on the ground surrounding the base of the tree and within the textured bark. In about 10 days, the adults emerge to start the cycle again.
January to March – The second cycle will have been completed. By the middle of March, the beetles disappear and find shelter to hibernate for the winter.
The adult beetle is about 6mm long and generally has yellow and black stripes on its back.
The larvae are in a grub form and also have yellow and black stripes.
The eggs are in rows or clusters, are bright yellow and are laid on the leaves.
Treatment of Elm Leaf Beetle
There are a number of methods that can be used to treat Elm Leaf Beetle infestations including spray application, soil injection and stem injection. The method we use is stem injection which involves injecting a chemical that is registered and approved for this purpose underneath the bark of the tree where it is transported by the trees vascular system into the canopy where the pests are active.
Why use stem injection?
Stem injection is the preferred method of treatment for the elm leaf beetle as there is no release of the chemical into the surrounding environment. Elm Leaf beetle treatment is long lasting and there is no risk of chemicals leaching through the soil profile – this means no harm to soil organisms such as earthworms and microbes / fungi and no contamination of groundwater or water table. Surrounding plants are unaffected by the treatment so the risk to foraging bees is greatly reduced.
Utilising specialist equipment, stem injection is the safest method of pesticide delivery, it allows for a precise, targeted dosage and uses less pesticide than both spray application and soil injection.