Question
I have an old willow tree that is almost dead now. There are lots of white worms inside the wood near the base of the tree and they are eating it to death. These worms are articulated, white and about an inch or so long. They have black mouths. How can I kill them. The tree is soon coming down, as I am in the process of removing it one stock at a time.

Answer
These are insects called borers.
Cracks and holes in the bark of branches and trunk. Larval feeding weakens tree stems. Upper portion of the tree, or possibly the whole tree may be broken or dead. Trees that are 2 to 3 years old appear to have the most damage.

Damage begins by adults drilling into the bark to lay eggs. The eggs then hatch into white, legless, C-shaped larvae that burrow just under the bark, then move deeper into the tree where they excavate tunnels. This results in splitting stems and openings. Sawdust-like frass is pushed out through the holes as tunnels are made. Sap and red-brown and white shavings may also ooze out of openings commonly found around the base of the stems. Larvae often bore around a branch or stem, girdling it and preventing the transport of water and nutrients beyond that point. The larvae pupate in cells at the end of the tunnel and emerge through a round hole cut in the bark as an adult.


If the number of infected trees is small, larvae can be removed by probing in the excavated tunnel holes with a flexible wire. A registered insecticide may also be injected into the holes to kill larvae. The holes then need to be plugged to prevent the fumes from escaping. Control of larvae should be done when sawdust is evident. A residual insecticide can be sprayed on the bark of tree trunks and branches. One application should be made in early June and a second application in early September. This can control the adults, killing them as they crawl over the surface before they lay eggs. The poplar and willow borer may require 2 to 3 years to complete its life cycle. The timing of developmental stages may differ and overlap from year to year.

I would use a newer insecticide called Merit. It is a systemic insecticide and will penetrate the bark and wood better than other insecticides.