If you own an Elm tree, you’re part of a special group. Australia has a significant portion of the world’s mature Elms because millions were devastated across Europe, Asia and America by Dutch Elm Disease. The tree is known for its beautiful form, dense summer shade and captivating autumn colour.
Elms have been planted in the Canberra region since the beginning of European settlement. There are now around 10,000 Elms in the ACT. Some specimens are over 100 years old and still going strong. In recent years, our Elms have had to contend with Elm Leaf Beetle which feed on its leaves. Left untreated, Elm Leaf Beetle can defoliate a whole Elm in one season and ultimately kill the tree. The good news is, there is chemical and organic treatment available to help protect them.
What is an Elm Leaf Beetle?
Elm Leaf Beetle is a non-native pest which feeds exclusively on the leaves of Elms of European and American origin. English elm, Dutch elm, Scotch elm, American elm and Golden elm are all on the menu for Elm Leaf Beetle. Chinese elm and Japanese zelkova aren’t as appealing and feeding on the foliage of these species is rare. There are no natural predators of Elm Leaf Beetle in Australia and since their arrival, their numbers have increased largely unabated.
The spread of Elm Leaf Beetle
The first recorded sighting of Elm Leaf Beetle in Australia was in Victoria in 1989. The beetle has spread and infestations have been recorded in Adelaide, Tasmania, Canberra and Sydney. It’s not clear exactly when Elm Leaf Beetle arrived in the Capital, but anecdotally, it has been here since at least 2010. Since that time, their numbers have exploded to the point where it’s extremely rare to see an Elm tree without a small amount of damage. Adult beetles can fly, but usually no more than 5 kilometres. The most common cause of the spread of the Elm Leaf Beetle is catching a ride on vehicles or humans.
What to look out for
If your Elm is suffering from an Elm Leaf Beetle attack, you can see damage to the leaves in the form of ‘shot holes’ or leaf skeletons. Adult Elm Leaf Beetles arrive in Spring and feed on Elm leaves. From November, they lay small clusters of eggs on the undersides of the leaves which hatch within 7-10 days and feed immediately. By the end of March the larvae have fully developed, crawled down the trunk to pupate into adults and prepare to hibernate over the winter and lay eggs next Spring.
Elm Leaf Beetle won’t kill your Elm immediately but severe attacks over several years can significantly weaken the tree and make it susceptible to other pests and diseases. If left unchecked, Elm Leaf Beetle can contribute to an untimely and premature death of your beloved Elm. There are two types of treatment to consider:
Organic: through trunk banding which captures larvae descending down the trunk, or a soil nutrition program.
Chemical: through stem injection and sprays.
An Arborist with knowledge in both these types of treatments (like us!) can advise you which is better for your situation. If you suspect Elm Leaf Beetle on your Elm, contact us for an inspection and treatment plan.