Get to know the Elm Leaf Beetle
- The Elm leaf beetle is a yellow to olive green with black stipes on their protective wing covers and black spots on their thorax.
Elm leaf beetles are around 6mm in length.
- The beetles lay tiny lemon coloured eggs in clumps on the underside of leaves in spring, which hatch in 7-10 days.
- At first the larvae (grubs) are very small and almost black. The larvae increase in size through summer reaching a length of 12 mm, when they are black and yellow and ‘caterpillar-like’.
- Around December to January, the larvae migrate down the trunk of the tree to pupate (is the life stage of some insects undergoing transformation) in the soil or in crevices on the lower trunk.
- After 1 – 2 weeks, new beetles emerge and, in warm summers, the new generation carries on breeding.
- The new generation of beetles continue to feed on the leaves for several weeks.
- Elm leaf beetles hibernate in sheltered places during winter and emerge in spring to feed on the young leaves.
- When the weather starts to get cooler in autumn, the adult beetles see shelter for winter in peoples’ homes, wood heaps, sheds and cars. In spring, when the weather starts to warm up again, they re-emerge and start looking for Elm trees again.
Bad – The Elm Leaf Beetle is a species of beetle from Europe. It was found on Victoria’s Mornington Peninsula in 1989 and has now spread to throughout the east coast of Australia.
Elm leaf beetle adults leave holes in the leaves called ‘shot-holes. Elm leaf beetles larvae cause a different type of damage called ‘skeletonisation’, where everything is eaten except for the leaf veins. Skeletonised leaves turn brown and drop prematurely.
Adults and larvae together can cause severe defoliation of elms, which can weaken mature trees. Elms suffering from repeated elm leaf beetle attack are also more susceptible to other pests and disease.
Although a single, heavy infestation of Elm leaf beetles can completely defoliate an elm, the tree will send out new leaves in the next season. However, the growth of the tree will be affected and, if Elm leaf beetles are not controlled, the tree may eventually die after a few years. If the beetles are controlled early, then elm trees will recover.
A healthy elm is more likely to survive
Keep elm trees watered in dry periods. Fertilise in late winter with slow release fertiliser. Avoid compaction of soil over root zone. Encourage good soil conditions by covering the root zone with mulch rather than lawn.
People are often concerned that they have borers in their homes when they find large numbers of the Elm leaf beetles emerging in their homes. Elm leaf beetles will cause no problems to peoples’ homes; they just use them to stay warm and secure over winter.