Advice for the Home Gardener from the
Help Desk of the UC Master Gardener Program
of Contra Costa County
Subject: Grapefruit Tree vs Woodpecker
Cllient's Request: How can we keep a woodpecker(s) from making holes in the tree bark? We don't have any insects/ants on the tree bark and we're concerned that the damage will make the tree susceptible to disease. Thank you.
MGCC Help Desk Response: Thank you for contacting the UC Master Gardener Program Help Desk with a question about woodpeckers on your grapefruit tree. From our phone conversation this morning, I identified the culprits as sapsuckers. These drill a series of holes, usually in straight horizontal lines, in live trees so plant sap oozes out of the holes. Sapsuckers feed on the sap, as well as on any insects that become trapped in the sap. Most of the time, sapsucker holes do not cause problems for the tree. When there is continuous sapsucker activity that increases the lines of holes to a significant percentage of the tree's trunk area, it can weaken the tree and potentially kill it.
Physical exclusion is the best way to prevent any kind of woodpecker damage. There are several methods you might see mentioned to prevent such as frightening devices or repellents, but these are not typically successful as birds quickly become accustomed to the deterrent. Covering the trunk with something that will prevent access to the tree bark is the best way to get sapsuckers to move on. Sections of lightweight sheet metal or roof flashing are fairly easy to shape around the trunk. You can get rolls of aluminum flashing at home improvement stores. Heavyweight plastic material can also be used. Use duct tape to hold it in place. You can also use wire mesh such as chicken wire, especially if it's bunched up somewhat. You will probably need to cover a great deal of the tree's bark to prevent the birds from just moving to an uncovered area. Whatever you use to cover the bark, make sure it is not too tight--you want to leave room for the tree to grow--and remove it when the birds have moved on. Depending on the size of the tree, you could also cover the entire tree with bird netting that you securely attach around the low base of the trunk to prevent all access to the tree.
Woodpeckers drill holes in trees for a variety of reasons. The largest holes are drilled for nest construction, usually in dead trees. Acorn woodpeckers drill 1/2 inch holes in which they store acorns. Smaller random holes are those made while looking for food. Woodpeckers' sharply pointed beaks and long tongues are used for extracting larvae and other insects from wood crevices. This can actually alert you to burrowing insects damaging a tree.
This link is to more information from the University of California about managing woodpeckers: http://ipm.ucanr.edu/PMG/PESTNOTES/pn74124.html.
I hope this information is helpful. Please don't hesitate to contact us again if you have more questions.
Help Desk of the UC Master Gardener Program of Contra Costa County (SEH)
Notes: Contra Costa MG's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, email: email@example.com, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at http://ccmg.edu/HortCoCo/ You can also subscribe to the Biog.