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Spring 2009 Lecture

Tree Pests and Tree Health: Woody Plant Pests and Diseases

Julie Coop
Manager of Plant Health, The Arnold Arboretum

May 18
Newton Free Library
330 Homer Street, Newton Centre

To a packed house of tree lovers in the Library's Druker Auditorium, the Arnold Arboretum's Julie Coop spoke about tree pests.

Julie is the Manager of Plant Health for the Arnold Arboretum and is a certified arborist. She began her career with Harvard on the grounds crew at Case Estates in Weston. She was refreshingly "down to earth," bringing many samples of tree twigs and pests with her to pass around the audience. She seemed to really know and love all the trees and samples that she showed us.

She covered the topics a homeowner would want to know about the pests that we deal with here, how to identify them, how they are managed at the Arboretum, and what a homeowner can do. Topics included the hemlock wooly adelgid and the winter moth. These are both introduced insects with no or few local predators. She discussed how to manage them and noted that the winter moth, like the gypsy moth, will probably be seen in cycles. To protect your trees from repeated defoliation, which can kill the tree, you may want to have your trees professionally sprayed (timed in April/May just as the caterpillars are emerging, as they must ingest the chemical). If a tree has been defoliated it will quickly replace its leaves, and you can nurture it in other ways such as with mulch (2-4" of low flat mulch not touching the trunk and NOT in "mulch volcanoes" around the trunk!) and water if there is a dry spell, while you are considering what to do for next year.

Julie reviewed many other pests, some of which are not yet in this region and others that are more cosmetic than real threats to plant health. Emerald ash borers, willow leaf beetle, eastern tent caterpillar, and anthracnose, the fungal disease often affecting dogwoods, were discussed.

Julie spent the longest and scariest part of the program presenting the Asian Long Horned Beetle, which in August 2008 was found in Worcester and is now thought to have been there for seven to ten years. About 20,000 trees have been removed from the quarantine area of Worcester. She passed around samples of the beetles, their egg hole exit holes (when they emerge in mid summer), and their frass (the "sawdust" they drop from their borings), all of which are large and very distinctive. The exit holes are perfectly round at a half inch diameter and are always horizontal. A pencil inserted is horizontal, or parallel to the ground. Unfortunately the beetles are hard to spot, even by professionals, as their activity is often high up in the canopy of the tree.

The one good thing about Asian Long Horned Beetle - it does not fly! This explains its slow spread - the beetles crawl from their tree when it becomes overpopulated to the next tree via touching leaves and branches. Also there are quite a few species the beetle does not like: oak, all conifers, lindens, and beech.

We must all be on the lookout for ALHB. Another lesson is never to transport firewood - a prime way that insects are spread. Julie shared that the NASCAR route, with its roving campsites, is thought to be linked to the spread of insect pests.

This event was sponsored by the Newton Tree Conservancy, a new non-profit working to raise public awareness of the importance of Newton's urban forest and to promote the health of Newton's street trees and park trees. The event was co-sponsored by the Newton Conservators, the Arnold Arboretum, and the Newton Free Library (617-796-1360).

- Katherine Howard


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