Bill,

I just read an article you wrote about cypress tree problems, and I have one. Three months ago I planted five Italian cypress trees approximately three feet tall, 10 feet apart, in full sun. I planted them so that the original dirt level in the container, matched the dirt level of the hillside.

About a week later, I noticed my resident ground squirrels had made a burrow running right past the roots. About 25 percent of the roots were exposed to air and had no dirt around them. I put rocks in the burrow end to prevent the squirrels from returning and replaced the missing soil so the roots were covered again.

Since then, this one tree has been drooping its branches and is slowly turning brown and is now 30 percent brown. I have been watering them once a week, and the other four are completely green, with most branches pointing up. I will be planting four more at the end of September. If I wait another month and it hasn’t returned to green, I’m thinking or replacing it when I buy the other four. Did the squirrels exposing the roots damage this tree?

That letter was from an online reader in the San Diego area. It was timely, as I attended a landscape pest control applicator seminar here in Napa just last week. There was strong emphasis on natural predators for rodent control, and one of the speakers made her entire presentation on an innovative way to control ground squirrels.

There are plenty of them at certain locations in our area, usually in dry, fringe areas. I have seen active burrows, many times, around old oak trees but never saw or heard of them harming an old tree. References I’ve checked say they feed on greens, nuts and seeds, and they may chew on bark and drip irrigation lines.

The burrowing can be a big problem, especially where it creates a trip hazard for cows and horses, or disrupts the soil in levees.

The reader’s problem with the Italian cypress trees shows how the burrowing can be a problem in the landscape, by way of soil disruption, not direct feeding on roots. It is possible that the irrigation water drained into the burrow rather than soaking into the newly planted root ball.

With respect to legal protection of wildlife, as it says in “Wildlife Pest Control Around Gardens and Homes” (UC Publication 21385): “Most mammals and birds are protected (by law)…however (some) may be controlled in any manner the owner or tenant chooses.”

Ground squirrels are in that category.

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This link, http://ucanr.edu/sites/Ground_Squirrel_BMP/ provides a wealth of information on the subject. It covers about a dozen possible control methods with notes on timing, efficacy, cost, labor and restrictions: poison baits, fumigants, trapping, shooting, burrow exploders, burrow destruction and others.

The website does not mention the most interesting and apparently safe method of habitat modification presented by Lisa Park at last week’s seminar: “Organic and Green Solution to Ground Squirrel Problems”: Burrow Blocker.

The technology is simple. Using a trailer-mounted water tank and a hopper of sand, the applicator pumps a slurry of wet sand into the burrow. The water drains away, filling the hole with firm sand and, as their promo clip says, “hopefully” trapping the ground squirrels in the burrow.

Searching for verification of its efficacy, I turned up not much except the company’s own links. They make no specific claims on effectiveness and their blog provides some good background on other animals that might inhabit ground squirrel burrows, including burrowing owls—a protected species. I have seen these, too, in Napa County.

Choose your tools with care.

Bill Pramuk is a registered consulting arborist. Visit his website, www.billpramuk.com, email questions to info@billpramuk.com, or call him at 707-226-2884.

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