The Rockdale Gardener

Gardening Posts From Rockdale Cooperative Extension

Ambrosia Beetles Kill Japanese Maples

japanese maple dead

This Japanese Maple was attacked and killed by ambrosia beetles. The soil around the tree was waterlogged and this stressed the tree. The beetles smell the stress chemicals put out by the plant and attack.

If you own a Japanese maple, flowering cherry tree, redbud or any smooth barked tree, be vigilant! An insect pest is out there stalking your prized landscape tree. It is very tiny but it can bring even large trees down. This insect is an exotic invasive known as the Granulate/Asian ambrosia beetle.

The Asian ambrosia beetle was accidentally imported to the United States in some peach trees that arrived in North Carolina from China in 1974. Since then, this insect has spread all over the U.S. and has caused millions of dollars in plant loss. Every year, nursery owners spend significant money to prevent its damage in 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 a 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 usually but can just be loose dust. This is the key diagnostic feature of Asian ambrosia beetle damage. Scout for this sawdust in early spring on trees and shrubs.

aab sawdust on dead tree

Sawdust cased by ambrosia beetle tunneling is evident on limbs and on the ground and leaves beneath the maple.

The insect doesn’t actually eat the wood but excavates tunnels that serve as habitat. She carries a fungus on her back from her last home and introduces it into the tunnel. This fungus is what kills the plant. When her eggs hatch, the larvae feed on the fungus. Excess fungus not consumed by the larvae clogs the plant’s vascular system which causes 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. The Asian ambrosia beetle will attack almost any broadleaf tree or shrub of suitable size, whether the plant is healthy or not.

Almost the entire life cycle of the insect is spent inside the plant, making this beetle hard to control with insecticides. The only time it is out of the tree is when it emerges in early spring to either reinfect the same tree or to seek out a new one. Traps can be used to monitor the insect’s emergence in February.

Asian ambrosia beetles must be controlled, but how? Remember that the insect itself is harmless once it has tunneled into the tree. There are no systemic insecticides that are effective against it. The fungus the insect introduces actually kills the plant and infested plants usually die.

waterlogged soil drowned this maple

The soil at the root zone of this maple was waterlogged.

The best way to control Asian ambrosia beetle damage is by prevention. Stressed out trees attract ambrosia beetles!!! The Beetles can smell the sick trees from long distances. So avoid drought or over-watering, physical injuries and improper planting.

Applying a trunk spray of pyrethroid insecticides in late February or when the first beetle is trapped will offer protection. Homeowners should use outdoor tree and shrub insecticides containing bifenthrin. Affected plants and/or plant parts should be removed from the property. The trunks of remaining plants should be treated with an appropriate insecticide and monitored.

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