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Rodent control for vineyards: grapegrowers learn that eliminating pocket gophers is no simple matter.

It doesn't take dynamite to dispatch gophers--as Bill Murray memorably tried in the movie "Caddyshack"--but ridding a vineyard of pocket gophers can be challenging.

Roger Baldwin, University of California wildlife pest management advisor, visited the UC Davis Oakville Experimental Vineyard in Napa Valley to address practical ways that vineyard managers can deal with the pocket gophers. He discussed the many types of control: baiting with poison, poison gas, explosions and lethal traps. Some of the techniques can help with other rodents including ground squirrels and voles.

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. The wide wingspans of owls prevent them from reaching between most vineyard wires.

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 for this purpose. 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%, Baldwin 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%-93% of gophers.

He warned that the traps must be fastened in place and marked with flags so it is possible to 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, adding that he always wears gloves: Gophers don't seem to notice human scent, but they can bite. Baldwin added that you have to go through a vineyard at least twice, but 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, which suffocate the rodents. "They can give 70% control for ground squirrels, but gophers wall-off their burrows," he said. Gas cartridges shouldn't be used close to buildings.

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

Aluminum phosphide is classified as a restricted-use pesticide. It may be purchased and used only by certified applicators who 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.

Baldwin said that vibrating stakes and repellents advertised on TV aren't effective, either.

Explosive gas inserted in the burrows is a final method of control that 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 it can cause fires and damage pipes. It can also alarm neighbors.

While Baldwin said that academics were not entirely sure of the actual impact gophers have on vines, he said, "If they can't find other foods, they'll chew on vines, especially younger ones."

VIEW VIDEO: Watch an expert with Gophers Limited track a gopher burrow and set up a trap in a vineyard.

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Title Annotation:GRAPEGROWING
Comment:Rodent control for vineyards: grapegrowers learn that eliminating pocket gophers is no simple matter.(GRAPEGROWING)
Author:Franson, Paul
Publication:Wines & Vines
Date:Jun 1, 2012
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