About Elm Leaf Beetles

The Elm Leaf Beetle Pyrrahalta luteola, is a native of Europe and was first found in Australia in February 1989, along the Mornington Peninsula, in Victoria. The beetle has since moved throughout the state causing serious defoliation of elm trees in the summer months. More recently, the beetle has been discovered as far away as Geelong, Benalla and Mansfield. Repeated attacks cause the tree to decline in health and vigour, making it more susceptible to other pests and diseases that can ultimately lead to its death.

The Elm Leaf Beetle is a capable flier but is also spread by hitchhiking in vehicles, on people or in Elm tree materials, like leaf litter used for mulch. In Spring the adult beetles emerge from hibernation. They are about 6mm long, light yellow with black spots on their heads and a black stripe on the outer wings. When they begin to feed they cause tiny shot-hole appearance on the leaves. This turns the leaves brown and causes them to drop prematurely. In November/December the adults lay the eggs. These are lemon shaped, yellow and laid in double rows on the underside of the leaf.

The larvae hatch in about one week and start to feed on the leaves. The larvae are 12mm long, yellow and have two stripes along their back. When they are fully fed they start to move down the trunk of the tree to pupate in the ground or in crevices in the bark of the tree. The adults then emerge ten days after pupation. This occurs in late December through to March. By mid March the beetles will disappear as they hibernate to sheltered sites.

Control options for elm leaf beetle

Soil Injection

This method requires a specially designed soil probe to be used to inject Confidor, a low toxicity systemic insecticide around the feeder root zone of the affected tree. This chemical is then translocated up through the tree's internal transport system to the leaves where it is ingested by the elm leaf beetle.

Based on overseas experience, only a single application per year (or even less) is required. The impact on the environment is minimal and there are no long term effects on soil micro-organisms or earthworm populations.

This treatment should ideally be applied to the soil between August to November. The effectiveness and speed of uptake will be enhanced if the soil is damp at the time of application.

Canopy Spraying

Insecticide can be applied as a foliar spray to control immature larvae in late Spring/ early Summer. Whilst this treatment is effective, applications can be difficult for very large trees and requires the use of large amounts of insecticide. If applied at the right time it will prevent the larvae becoming adult beetles and feeding on leaves before descending the tree.

It should be noted that this method only provides one-off control which means that the tree may be re-infested by beetles from nearby trees later in the season. However, this treatment is the most effective option where quick action is needed with large infestations.

This treatment is usually used from November to March.