Advice From MGCC's Help Desk:  Thank you for contacting the Master Gardener help desk. Squirrels are very likely the culprits. They frequently chew bark on a wide variety of trees and shrubs to get at the sweet sap running just below the bark. This usually happens in the spring. The sap, running in what is called the phloem, contains nutrients made by the leaves that are being transported to other parts of the plant. The bark is the "skin" covering this vascular system. 

If the squirrels ate the bark only on one side of the branches (less than one quarter of the circumference), the branch will survive and the wound will eventually heal over without intervention. With more than one quarter eaten, the odds of survival decrease (if it's chewed all the way around, there's no hope). So, examine the branches carefully, prune back any with a lot of damage, and leave any with less damage. Don't use anything to cover the wounds. Research has shown that covering wounds can delay healing and encourage fungal growth. The tree can seal the injury and then cover it in time. 

Here is a link to information from the University of California on tree squirrel management:  http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74122.html. You will find a section that talks about exclusion, which is almost impossible in trees, but is really the only non-lethal method for keeping squirrels out of an area. While there are many squirrel repellents on the market (many licensed for use in California), they are not particularly effective. Also, tree squirrels become acclimated to sound and lights, so these don't work as deterrents, either. The information also talks about trapping and killing squirrels, but another squirrel may move into the open territory and continue the damage. It is not legal in California to trap and relocate squirrels (or any other animals). 

One possible solution to prevent the squirrels from eating the tree bark might be to use a motion-sensing water sprinkler (for example http://amzn.to/1IgUT3V)) aimed at where the squirrels access the tree. Squirrels don't like water, so this may work to keep them away. You should only need this in the spring and early summer while the sap is most attractive. Another possible solution is that if the only access to the tree is up the main trunk you might consider a sheet metal wrap of the main trunk covering at least 18", but it won't work if the squirrels can bypass by jumping from the ground or another source (fence, etc.)... and it wouldn't look too great (maybe paint it?). 

Good luck!

Master Gardeners of Contra Costa Help Desk

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Note: The Master Gardeners of Contra Costa's Help Desk is available year-round to answer your gardening questions.  Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA  94523. We can also be reached via telephone:  (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/

Advice for the Home Gardener from the Contra Costa Master Gardeners Help Desk

Client's Question and Concerns:
I'm trying to control gophers and squirrels on my property. I am worried that owls might harm my cat. Could you please let me know if this is cause for worry? If not, could you please send me some information.

CCMG Help Desk Response:

Thank you for contacting the Master Gardener help desk.

Rodents, especially voles, rats and gophers, are barn owls' favorite foods. They do a pretty good job of reducing the population of these unwanted pests. Barn owls are cavity nesters and will nest in artificial boxes. They are fairly tolerant of human activity and will nest quite close to houses, making them ideal predators for the rodents that plague our gardens. Barn owls are mostly white or light tan; their call is a loud screech.

Great horned owls do not use nest boxes, preferring large open nests. They, too, eat rodents, but will also take larger animals such as skunks. Great horned owls are larger than barn owls and are brown; their call is the stereotypicalHoo-h'HOO-hoo-hoo. Here is a link to the Hungry Owl Project in Marin County where you will find lots of information about owls: http://www.hungryowl.org/ 

Great Horned Owl
(Bubo-virginianus)
photo: owlpages.com

Barn owls are not a danger to an outdoor house cat, but certainly great horned owls are (skunks are about the same size as many house cats). If you have ever heard the great horned owl call in your neighborhood, you probably have them at least occasionally. They have pretty large territories.

To protect your cat, it's really best to keep it indoors, especially at night. There are lots of dangers outside besides great horned owls. Here's a link to American Bird Conservancy's Cats Indoors program that will give you lots of information about how to make an outdoor cat a happy indoor cat: http://www.abcbirds.org/abcprograms/policy/cats/index.html 

Gophers are a common problem for many of us in Contra Costa. These burrowing animals eat plants, sometimes causing a great deal of damage. Here's a link to information about controlling gophers: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7433.html

Not knowing if your squirrel problems are from tree or ground squirrels, I'm including links for information about controlling both species: 
tree squirrels:  http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74122.html and
ground squirrels:  http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7438.html 

Please don't hesitate to let us know if you have further questions.

Contra Costa Master Gardeners Help Desk

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Note: The Contra Costa Master Gardener Help Desk is available year-round to answer your gardening questions.  Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA  94523. We can also be reached via telephone:  (925) 646-6586, email: ccmg@ucanr.edu, and on the web at http://ccmg.ucanr.edu/Ask_Us/