Faithful reader, Charles, writes, “I have a problem with my crepe myrtle that started about three weeks ago. There are long worm-like things of a sawdust consistency coming out from the trunk. The trunks with these things are losing their leaves. I believe they are due to a kind of Asian beetle. I have not seen anything that cures the situation and I am coming to you as a last resort. Could you please help me?”
Grumpy’s 275% Guaranteed Correct Answer: Your crepe myrtle is infested with tiny, brown Asian ambrosia beetles. Female beetles bore into the trunk and branches in spring and summer to deposit eggs. The “worm-like things” are strands of sawdust pushed out by the beetles. The beetles themselves don’t harm the plant, but the ambrosia fungus the beetles carry does. It prevents water and nutrients from moving up and down the plant, as evidenced by yellowing and dropping leaves. Seriously infested plants can’t be saved. They should be removed immediately to keep the infestation from spreading.
My advice to Charles right now is to remove any infested trunks and burn them or bag them and throw them out with the trash. Then treat your tree according to label directions with a systemic insecticide called Bayer Advanced Tree & Shrub Insect Control that’s applied as a drench and absorbed through the roots. You’ll need to apply it every spring. As an alternative, you can spray the trunks with a long-lasting contact insecticide such as permethrin or bifenthrin. You’ll find Ortho, Spectracide, and Bayer Advanced products that contain them. Spray once a month from March to September.
Unfortunately, these ambrosia beetles target more than crepe myrtles. They also attack Japanese maple, cherry, plum, peach, dogwood, pecan, and redbud trees, among others. So be vigilant.