Elm Leaf Beetle
Elm Leaf Beetle (ELB) was accidentally introduced into Australia in the late 1980s. In the last few years it has established itself in South Australia and across Adelaide’s Elm Tree population. Both the adult and the larval stage of ELB feed on Elm Trees and can cause complete defoliation of a large Elm Tree in the course of a single summer.
ELB can cause unsightly damage to Elm Trees as a result of the adult beetles and larvae feeding on the leaves. Repeated seasonal defoliation can cause a decline in tree health, reduced growth and an increased susceptibility to environmental stresses.
Although heavy infestations of ELB can completely defoliate an Elm, this does not occur until late in the season. The Elm will grow new leaves in the next season. However, the growth of the tree will be affected and ultimately ELB may lead to its demise. By taking steps to control ELB populations, the damage can be significantly reduced.
Although most elms planted in Adelaide are susceptible to ELB, a healthy tree is more likely to recover from feeding damage. To keep trees healthy:
- Keep the tree watered in dry periods.
- Fertilise in late winter with a slow release fertiliser.
- Avoid compaction of the soil over the root zone.
- Encourage food soil condition by covering the root zone with mulch.
ELB Control Measures for the Private Gardener
Trunk Banding is the simplest way of breaking the lifecycle of the ELB. It needs to be applied during the descent of the larvae down the trunk, at the stage of pupating (usually December). Unfortunately, Trunk Banding does not prevent re-infestation from untreated Elms. Therefore it is most effective in situations where other Elms in the neighbourhood are treated.
Non-poisonous sticky substances marketed for insect control, may be available from horticultural suppliers. This can be applied in a band around the tree trunk to trap the descending larvae. The sticky side needs to be facing outwards in a band approximately 200 mm wide. The larvae adhere to the tape as they descend the trunk.
The tape must be renewed if it gets covered with larvae, or affected by the weather. This method is environmentally safe but is only suitable for smooth barked Elms and may not be effective against heavy infestations.