Woodpeckers, primarily sapsuckers, occasionally damage trees by boring a series of 1/4- to 3/8-inch closely spaced holes in the limbs or trunks of healthy trees. They feed on sap oozed from the holes. The tree wounds may attract insects, squirrels, or porcupines and can serve as entrances for diseases and wood decaying organisms. Occasionally, girdling of limbs and trunks may kill the tree.
High value ornamental or shade trees can be protected from sapsuckers by sticky bird repellents such as Tanglefoot®and Roost-No-More®. These products may be smeared on trunks and the top of branches to discourage sapsuckers. Hang frightening devices such as bright tin lids, plastic or mylar strips 1-inch wide and about 2-feet long or hawk mobiles in the trees so that they move in the wind to frighten sapsuckers. Mirrors that enlarge the image may also frighten sapsuckers. Woodpeckers are protected by federal and state laws.
For more information, see the following Colorado State University Extension fact sheet(s).