Elm leaf beetle threatens shade Trees.

Melbourne's and Geelong's reputation as the garden state is under threat from the voracious elm leaf beetle.

Thousands of elms are being stripped and killed as the beetle goes on its worst-ever rampage. Valuable and sentimental avenues of honor, particularly in previously immune country areas, are now under threat as the gluttonous bugs spread north. Since being found on the Mornington Peninsula in 1989, the beetle has spread across Melbourne, the Dandenong Ranges, Gippsland, Yea, Marysville, Alexandra, Benalla and Geelong.

Where ever I have lived, I've always used Elm trees in various forms to underpin plantings of Alpines and Bulbs.

Conservative estimates have valued mature elms at up to $10,000 each, meaning an economic impact of up to $700million if the bug wipes out Victoria's elm stocks. One of the worst-hit areas is the City of Banyule in Melbourne's east, thankfully a long way from Geelong.

Every one of the estimated 7500 trees in the city are under attack.

The beetle hitchhikes on cars, caravans and other vehicles, jumping off at new hunting grounds.

Some areas, such as the City of Melbourne, which has 6000 elms, have used a management plan and spent thousands of dollars safeguarding trees.

There are an estimated 70,000 elm trees in Victoria, most of them in metropolitan Melbourne, with another few thousand in Geelong.

The beetles can kill even the biggest trees within years through annual attacks if not checked.

The adult elm leaf beetle is about 1/4 inch long, yellow-green in colour, with a black stripe on the outer edge of each wing cover. The adult chews the rectangular shaped areas or shothole patterns in the leaves. The larvae, which are the caterpillar-like immature stages of the beetle, grow from about 1/4 inch to about ½ inch in length.

They are black at the smaller growth stages and dull yellow or greenish with two dark stripes and black spots as they get larger. They are present later than the first early generation of adults, and are responsible for the skeletonizing damage to the leaves that leaves only the veins. Eggs are laid in double rows of 5 to 25 on the undersides of leaves.

When the larvae are mature, they crawl down to the base of the tree trunk, where they form yellow pupae, which is the cocoon-like stage. Many times there can be very large accumulations of the pupae on the ground.