Appearance

• Adult willow borers have black bodies that measure 1/4 to 1/2 inch long and feature curved snouts. The ends of their wing covers vary in color from grey to white. The larvae measure a little more than 1/4 inch and are creamy white and "C" shaped.
  
  

Life Cycle

• Adult weevils emerge in spring and feed on the phloem of young shoots. Females chew into the bark of stems during the summer and deposit one or more eggs within two to 10 days after emergence. Upon hatching, the larvae bore tunnels through the bark and wood, pushing out a sawdust-like material called frass into the stem around the holes. Although the adults can fly, they rarely do so and are mostly sedentary. Adult willow borer activity on the tree is most apparent in the morning and evening. The larvae overwinter in the tunnels while adults overwinter in plant debris. A willow borer takes one to three years to complete its life cycle.
  
  

Damage

• Initial symptoms of willow-borer infestation includes dead patches or cracks on the bark of the trunk and branches, and holes caused from chewing the bark on the lower parts of stems. The tunnels caused by feeding larvae can kill willow saplings, especially those already stressed due to improper growing conditions. Large infestations of borers on willow and poplar trees weaken stems and branches, making them susceptible to breakage during high winds or heavy snow.
  
  

Treatment

• Confirm the presence of willow borers on your trees before treating them. In spring, inspect the tree for the presence of adults, or look for holes along the lower parts of stems with sawdust around the edges. Prune infected parts of the tree with sharp, sterilized pruning equipment to control spread. Treat stems and branches with a chemical insecticide containing imidacloprid or permethrin when adults are most active. Follow label directions for application rates. Collect clippings and debris from around the base of the trees to prevent the adults from overwintering.