Growing & Winemaking


Rodent Control for Vineyards

June 2012
by Paul Franson
It doesn’t take dynamite to dispatch gophers—as Bill Murray memorably tried in “Caddyshack”—but ridding a vineyard of pocket gophers can be challenging.

An oversubscribed group of grapegrowers gathered recently at the University of California Davis’ Oakville Experimental Vineyard in Napa Valley to hear practical ways to deal with the pernicious pests from Roger Baldwin, UC IPM statewide vertebrate control advisor.

Some of the techniques also can help with other rodents including ground squirrels and voles, but the talk was aimed at pocket gophers. Baldwin discussed the many types of control: baiting with poison, poison gas, explosions and lethal traps.

Predators not effective
Owls and hawks are popular sights in a vineyard, but Baldwin said that even though these birds of prey can eat huge numbers of rodents, they can’t keep up with the fecund animals; neither can gopher snakes, coyotes, cats or other predators. Voles and ground squirrels are easy targets for avian predators, but gophers spend most of their time underground. Their wide wingspans prevent owls from access between most vineyard wires, anyway.

Baldwin mentioned that flooding can be effective, but few vineyards are now irrigated with that method, and few growers would be inclined to use precious water. Disking can destroy tunnels and kill some gophers, too, he said.

Generally, it takes more than one technique to reduce gophers to a manageable population—a reduction of about 78%, he suggested.

The first step is teaching vineyard workers to identify fresh gopher mounds: closed, with wet-looking dirt. Training by an expert increases effectiveness significantly. Then you can probe for the tunnels—Baldwin uses a long screwdriver. He said that traps and aluminum phosphide pellets are the most effective controls.

Killing gophers with traps
Some traps are effective for larger animals but too big for gopher tunnels. Baldwin finds the classic box trap like the Victor effective for small areas, but they’re big and bulky, requiring extra time to place in tunnels.

Instead, he recommended puncture traps like Macabee Gopher Trap, or his favorite, the Gophinator, which are small and easy to position in tunnels. Baldwin said that in trials he conducted, these killed 77% to 93% of gophers.

He warned that the traps must be fastened in place and marked with flags, so you can find them again. Wounded animals might otherwise drag the traps away; predators can learn to dig up dead animals conveniently marked by the flags.

Baldwin recommended a Japanese hori hori gardening knife for digging out the holes to place traps, and said he always wears gloves: Gophers don’t seem to notice human scent, but they can bite. He added that you have to go through a vineyard at least twice; kills are usually quick, within a day.

Baiting with poison
Baiting with poison is another technique. Special probes that release bait are available. Strychnine and zinc oxide are legal in California for ag use, and they kill with one feeding.

Anticoagulants may take multiple feedings. Poisons can have secondary effects, however, if other animals eat the dead rodents.

Baldwin said that baiting can be effective, and he has seen 30% to 50% control. “The effectiveness depends on what other foods are available to the gophers. They don’t normally eat seeds, which are used as bait.”

Tractor-drawn devices can create artificial burrows and deposit bait as they do, but soil conditions are critical for effectiveness.

Gassing gophers
Baldwin says that fumigation is an effective way to eliminate burrowing pests. Gas cartridges release carbon dioxide and carbon monoxide that suffocates the rodents. “They can give 70% control for ground squirrels, but gophers wall-off their burrows,” he said. These shouldn’t be used close to buildings, however.

Baldwin said that aluminum phosphide tablets, which release toxic phosphine gas when moistened in a tunnel, are very effective against pocket gophers. They can also be ingested with bait. “You get close to 100% kill.” There is no mechanical probe for inserting it, however. You have to probe, drop in the tablet and close the hole.

Aluminum phosphide is classified as a Restricted Use Pesticide, so it may be purchased and used only by certified applicators. You have to be licensed, file an intent and report to use it and post signs around the site. It can’t be used within 100 feet of a building.

Flares are not legal for fumigation in California, by the way, nor is use of vehicle exhaust. A machine made for this purpose is also not legal.

To questions from the audience, Baldwin said that vibrating stakes and repellents advertised on TV aren’t effective, either.

A final method of control is a gas explosive inserted in the burrows; this is supposed to kill gophers with concussion. While acknowledging that it can be satisfying a few times, Baldwin says it really isn’t very effective, and can cause fires and damage pipes. It can also alarm neighbors.

Ironically, Baldwin concluded his talk with the admission that we’re not entirely sure of the actual impact gophers have on vines. “If they can’t find other foods, they’ll chew on vines, especially younger ones.”


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