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Look out for Elm Leaf Beetles in Canberra

Posted on October 15, 2014 3:12 am.

Elm Leaf Beetle

We have had calls from people who have discovered Elm Leaf Beetles lurking in their elm trees in Canberra and the region this week. If you spot these little guys with their racing stripes on your elm tree we can help you out.  The best time to treat your trees for Elm Leaf Beetle is now!

The Elm Leaf Beetle(Xanthogaleruca luteola) is about 4-6mm long, olive and black with two stripes. The beetle and its caterpillars can totally destroy an elm tree in one season. As elm trees come into leaf with the arrival of spring the adult beetle emerges from its winter hibernation. The beetles feed on the leaves in the canopy of the tree where they lay yellow eggs on the underside of the leaves that then hatch as black and yellow caterpillars or larvae. The larvae feed on the green tissue of the underside of the leaf. The larvae then crawl down the trunk and pupate in bark cracks or around the base of the tree. The pupate emerge as adult beetles and return to the foliage to continue the cycle of destruction.

Life cycle

  • March – September: Hibernation
  • October: Beetle emerges
  • November: Eggs laid
  • December: Larvae
  • January: Pupae
  • February: New adults

Symptoms

  • Leaf damage to elm trees occurs between August and February.
  • Shot holes in the leaves caused by the adult beetles.
  • Skeletonisation of the leaves caused by larvae.
  • Defoliation where leaves are falling off out of season around August to November.
  • Discolouration can be another sign around December to February.

Prevention

Keep elm trees free of dead limbs and suckers as well as minimizing drought stress to give them better resistance.  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.

Treatment The Elm Leaf Beetle will never be eradicated but it can be managed.Early treatment is essential and can include:

  • Trunk injection  with Imidacloprid* is considered to be the most effective and environmentally sound option. The insecticide is injected directly into the trunk of the tree. The tree transports the chemical to the leaves where it kills the beetles. Tree trunks must be >200mm diameter. Beetles only need to ingest a small amount of leaf material for the chemical to kill them; you will see dead and dying beetle on paved areas. Trunk injection is safe around children, pets and riparian situations.
  • Canopy spraying Foliar sprays can be used on young trees towards the end of October but are often impractical on older trees due to the size of large elm trees. Foliar sprays need to be applied annually.
  • Non-chemical control banding is a safe non-chemical control that sometimes works to trap larvae that migrate down the trunk between December and early February. Adhesive tape can be wrapped around the trunk in a strip about 20cm wide, with the sticky side facing out. This can help to break the Elm Leaf Beetle lifecycle. The bands need to be applied before the larvae start to crawl down the trunk, which can vary depending on the weather each season, so close monitoring is essential. Banding treatments may need to be reapplied several times each season if beetle numbers are high. These methods will not reduce damage in the initial year of application, but should reduce beetle numbers and damage in subsequent years. This method, while environmentally safe, may not be effective against heavy infestations.
TreeWorks does not recommend soil injection which involves injecting the soil under the drip line of the tree and can be applied to trees of any diameter. Soil injection requires up to 100 L of water per tree and is not recommended when soil moisture is low. 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 the larvae. As the movement of the chemical is slow the injections need to be carried out around 6-8 weeks prior to the beetles emerging from hibernation. Soil injection is detrimental to soil flora and fauna, including earthworms and mycorrhiza. Applications near creeks and rivers or near food gardens pose particular risks for invertebrates and human health as it will kill everything in the soil.
Timing – The best time to treat elm trees is NOW.  Stem injection can be done any time but ideally before the beetles have laid their eggs or just after the eggs hatch.  Trees should be treated every three years.


TreeWorks is a leading tree services business operating in Canberra, Monaro, Southern Tablelands, Southern Highlands and Sydney. We are a fully licensed, ACTEW accredited & insured tree surgery company and a member of Arboriculture Australia. Our climbers are appropriately trained and some of our arborists have over 25 years experience in large scale tree surgery and removals. Call 1300 135 835 or visit www.treeworks.net.au for more information.