Question
I have three weeping willows near Sacramento , Ca.  I have water going directly to each tree.  They are about 9 years old.  They look puny & several branches have died.  I broke off a branch & a white worm was inside.  Anyway to get rid of this worm?  
Thanks. Tina

Answer
Sounds like the black twig borer. The black twig borer, Xylosandrus compactus, is one of the few ambrosia beetles that attacks healthy plants! This beetle is very small, dark and more or less oval in top view. The largest specimens are just over one-sixteenth inches long. Female beetles attack twigs or branches and bore in to the pith (or if the twig is large, they bore into the wood about half to one and one half inches). Black twig borers are capable of laying eggs without mating (parthenogenesis). Males occur rarely and do not leave the brood chamber as males cannot fly. After the females bore into a twig, they form a small chamber in which the mostly female eggs are laid. The tiny grubs feed on the fungi that grow on the walls of the brood chamber. The grubs pupate and then (if males happen to have developed) the new beetles mate before leaving the twig to infest new twigs. If the twig is small, only one female will attack it. If the twig is more robust, up to 20 females will attack it. In the summer it takes about a month from egg to adult beetles. In the winter, development is much slower. The adults overwinter inside the damaged twigs. At least one of the fungi in the ambrosia is Fusarium solani. Infested twigs usually dieback to a point below the brood chamber. Although the ambrosia usually does not kill the whole plant, the dieback of twigs can have considerable impact on the appearance of infested trees and shrubs. Over 224 plant species in 62 families are susceptible to the black twig borer.
Once the beetles are noticed attacking an ornamental plant, the plant may be sprayed with an insecticide called bifenthrin Merit or Onxy to prevent further attacks and kill the insect in the wood. Any infested twigs and branches should be pruned off and destroyed. If the infestation is discovered in the spring, it may take several applications spaced out at six-week intervals to completely protect the plants. There are two factors that may give long term control. If we have a harsh, cold winter, the weather will probably kill the black twig borers back to southern Georgia. The other factor most folks have a little more control over is fertilizer. Some feel that the black twig borer is going to infest trees and shrubs that are fertilized (or that grow in a lawn that is fertilized).