I have a few willow trees in 5 gallon pots that I started from cuttings last winter. Just today I noticed that a couple of them have dark areas on their trucks with little holes along with wood dust coming out. I cut one of my trees right where the dark area and dust covered hole was and found a little white larva inside. What is it? Will it destroy my trees? How can I prevent this? Please help!!

Thank you for your time,

Ellysgarden