We have a nasty little visitor from Asia that I wish we could build a wall to keep out.
The Asian ambrosia beetle was accidentally imported to the United States in some peach trees in North Carolina that had arrived from China in 1974. Since then, this insect has spread all over the U.S. and has caused millions of dollars in plant loss. We are getting multiple calls about this destructive beetle. We don’t need to vet these guys before deporting; we need to send them straight home. Do not pass GO. Do not collect $200.
These small beetles are tiny blackish brown and resemble southern pine beetles in size and makeup. 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 not caring whether the plant is healthy or on the decline. 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 this pesky insect eats her way through the tree, she ejects sawdust out of the entrance hole called frass. 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 early spring on trees and shrubs. Once the female beetle digs her hole, she deposits her eggs.
The problem with seeing these toothpicks is once they are there; the plant is a goner. The beetles are active year-round, but activity usually starts sometime in March. You can have several generations per year. Unlike pine beetles that eat the sections of the trees that move water and nutrients up and down the tree, the Asian ambrosia beetle does not feed on the wood. These mothers actually leave a fungus (ambrosia fungus) to provide a first meal for her larval offspring. Once the beetle introduces the fungus, the disease damages the tree’s xylem tissue which prevents the tree from transporting water and nutrients. The entry holes also create entry points for other disease-causing fungus to attack the plant. Any of these can result in the death of the plant.
A protective spray with bifenthrin or permethrin insecticides can be used to keep the insects from attacking the plants in early spring and repeated every six to eight weeks.
But once the plant is attacked, there is nothing you can do but administer last rites and put it on the funeral pyre.
Seriously, infested plants should be removed from the property and burned or chipped up.
Reach Campbell Vaughn, the agriculture and natural resources cooperative extension agent for Richmond County, by e-mailing firstname.lastname@example.org.