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Skaggs: Watch out! Ambrosia beetles will do damage
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Center for Invasive Species and Ecosystem Health — Bugwood Network: Find more information on Asian ambrosia beetles and other insect pests.

Over the last several weeks, I've received numerous calls concerning a particularly damaging pest of landscape trees.

If you own a cherry tree, Japanese maple or crape myrtle, be vigilant! The culprit is very tiny but it can bring down even large trees. The insect is a beetle known as the Asian ambrosia beetle.

The Asian ambrosia beetle was believed to have been accidentally imported into the US in 1974. The beetles hitchhiked on some fruit trees that had arrived from China.

Since then, it has spread all over the United States and has caused millions of dollars in plant damage. Until the last few years, nursery owners were the primary defenders against this pest, but it has become much more prevalent in landscapes across the Southeast.

The female Asian ambrosia beetle emerges in spring from her winter habitat inside an infested tree and travels to a suitable nearby shrub or tree.

She looks for a small plant or limb 1 to 2 inches thick and begins to bore into it. She moves fast, eating her way through an inch of wood per day.

As the insect eats her way through the tree, she ejects sawdust out of the entrance hole. The sawdust exiting the hole forms toothpick-like protrusions. This is the key diagnostic feature of Asian ambrosia beetle damage. Scout for this sawdust in spring and early summer on trees and shrubs.

The insect doesn't actually eat the wood but excavates tunnels that serve as habitat. They introduce a fungus into the tunnel, which is carried on the females' back from her last home. When the eggs hatch, larvae feed on the fungus. It is this fungus that eventually kills the tree; it clogs the vascular system of the plant causing it to wilt and eventually die.

Many species of trees and shrubs are susceptible to this beetle. I have observed them attacking Tulip poplars, oaks, ornamental cherry, crape myrtle, redbud, hickory and Japanese maple. Asian ambrosia beetle will attack almost any broadleaf tree or shrub and that is a suitable size - healthy or not.

Almost the entire life cycle of the insect is spent inside the plant, making the beetles hard to control with insecticides. The only time it is out of the tree is when it emerges in spring to either re-infect the same tree or to seek out a new one.

Asian ambrosia beetles are difficult to control. Systemic insecticides are not very effective against the beetles once inside the tree. Actually, the beetle is harmless; the fungus actually kills the tree. Infested trees will most likely die.

The best way to control the beetles' damage is by prevention. Trunk sprays using pyrethroid insecticides applied in late February and March offer protection. Homeowners should use outdoor tree and shrub insecticides containing imidacloprid or bifenthrin (brand names include Ortho Bug-B-Gon Max and Bayer Advanced).

Most importantly, be sure to remove affected plants or plant parts immediately upon seeing the damage.

Also, don't place these items in the compost pile. The trunks of remaining plants should be treated with an appropriate insecticide and monitored.

Billy Skaggs is an agricultural agent and Hall County extension coordinator. Phone: 770-531-6988. Fax: 770-531-3994.