Elm Leaf Beetles get the tree-tment

Wednesday August 16.

An infestation of Elm Leaf Beetles last Summer, left the city’s Elm trees with skeletonized leaves or defoliated tree canopies.

The beetles won’t kill Elm trees but repeated, long-term leaf damage can have a significant impact on a tree’s health.

Orange City Council’s City Presentation Manager Nigel Hobden said now was the ideal time to begin treatments using insecticides in a bid to prepare the trees ahead of the warmer months.

“We’re using two different methods to control the Elm Beetles depending on the size and age of the tree ; inserting tablets into the soil or making injections into the tree trunk,” Mr Hobden said.

“You might have noticed that bitumen has been removed around the base of some street trees over the last few months. In younger, smaller street Elms we’ve been digging several pesticide tablets into the ground around the roots of the trees.

“The tablets will dissolve over time, the tree roots will absorb the insecticide and carry it to the tree’s leaves. This week’s rain will help dissolve the tablets.

The beetles will hatch in the warmer months, travel to the top of the tree, eat the leaves and be affected by the insecticides. Mr Hobden said the tablets did not impact on the health of the tree nor the nearby biodiversity in the soil.

However, older, larger trees needed to be treated differently using injections straight into the trunk of the tree.

“We’ll be injecting the older and larger trees with insecticides in the coming weeks as the trees start to bud. The sap will take the pesticides up the tree and into the leaves in a similar way to how the tablets work.

“For this reason, we’re asking the community not to place the adhesive tape around street trees at this time of the year. It’s important the beetles can reach the top of the tree to eat the leaves in order to ingest the insecticides. For that reason, residents can expect to see leaf damage again this year, but it’s a step in the right direction.”

Mr Hobden said residents could treat any Elm trees on their own private property using store bought tablets around the trees’ base, but larger trees would need an injection into the trunk.

The tape can be effective in trees that have not had insecticides used on them and people are welcome to use tape on their own trees in their backyards.

“It’s important residents seek advice from a qualified arborist to understand what treatment is best for each tree,” Mr Hobden said.

BACKGROUND INFORMATION :

The life cycle of the Elm Leaf Beetle (ELB) has the adults emerging from hibernation under the ground about October and they lay eggs in November.

Both the adult beetles and larvae feed on the leaves; the adults producing a ‘shot hole’ like appearance to the leaves and the larvae skeletonizing the leaf tissue.

Using an insecticide that is transported to the leaves and is then ingested by the beetles and larvae, will assist with controlling the ELB population and reducing the overall damage to the tree.

When a larger tree is injected, the insecticide, will be transported via the sapwood up the tree and into the leaves in a similar way to how the tablets work.

Banding trees with adhesive tape is effective when the larvae are moving down the trunk to pupate in the ground, as such banding can assist in a life cycle interruption and is generally performed in late December and January when the larvae crawl down the trunk.