HOPLAND, Calif. – Call them mutton mowers.
University researchers are training sheep to clean up vineyard weeds but stay off the grapes.
Enthusiastic and unpicky eaters, sheep are already being used in some vineyards as a green alternative to tractors.
They don't use gasoline and keep down weeds — a necessary task to deter pests and keep vines healthy — sans herbicides.
Unfortunately, sheep will chew up thousands of dollars worth of grapes if left to their own devices.
Sheep ranchers get a new market for their flocks while vineyard managers get "another tool in the tool box," says Doran. "It's a win-win."
But just how do you teach sheep?
It's not as tough as you might think, says Doran, who thinks sheep are unfairly maligned as wooly minded creatures.
They may not be the brightest lights around, but "they're very good at what they do," he says.
What they do is eat — all day, every day.
"Everything that we're doing is based on their skills at eating different foods and detecting different flavors and associating positive or negative effects of those foods with different flavors," he says.
Doran's project is based on the recommendations of aversion therapy techniques developed by an animal behaviorist at Utah State University .
Sheep that had never tasted grape leaves were brought in and allowed to stuff themselves on vines.
The animals then got a small dose of lithium chloride, a drug that doesn't produce any outward signs in the dosed sheep but leaves them feeling queasy, Doran said.
Some sheep got the dose in liquid form, some in capsules and two other groups of sheep got placebos to serve as a control.
Sheep that were dosed generally left the grapes alone when set loose in an experimental vineyard at the UC Hopland Research and Extension Center south of Ukiah, Doran said.
A recent visit to the vineyard showed tangible results: bunches of fruit hung on the vines weeded by trained sheep. Vines mowed by untreated sheep were ragged and bare up to the sheep's head height.
Interestingly, it seems sheep may have discriminating palates. The untrained sheep largely left alone a red grape called aglianico but appeared to be big fans of chardonnay.
Untutored sheep make good mowers, but they must be deployed carefully.
Some vintners use them in the cold months, when vines are dormant and there's not much to nibble on. Others have tried miniature breeds that are too short to do much damage, though such animals are expensive and in short supply.
Don Watson, owner of Wooly Weeders, a Colorado-based company that also provides mowing services in the Napa Valley, doesn't think aversion therapy is necessary.
He says he achieves excellent mowing results by using top-notch sheepherders and dogs to move the sheep along before they can get to the vines.
He puts sheep into the vineyards only at certain times of the year, such as when berries are at their most astringent and unpalatable to the animals.
He also employs lambs, which are shorter and less likely to reach high enough to damage vines.
"It's better to take a more direct route, observe animal behavior and merely adapt our management to suit that behavior," he says.
Doran says it's good to be skeptical of the aversion technique — and any new technology — but he says trained sheep could be used more widely and in the spring months when floor vegetation grows rapidly.
He and his colleagues would like to develop an alternative to lithium chloride, such as naturally occurring tannins. They also hope to look at what effect sheep may have on the soil and grape quality, not to mention their fertilizing capabilities.
Sarah Cahn Bennett, co-owner and enologist at Navarro Vineyards in Mendocino County's Anderson Valley, is interested to see how the training comes out, although she'd be more comfortable using a natural agent to produce the aversion.
Navarro doesn't use herbicides or pesticides so weed-removal is done either by hand or by tractor. The winery also uses sheep, but that takes a lot of management and can't be used in every setting, says Bennett.
Perhaps some day sheep may safely graze in a vineyard without putting the fruit in danger. For now, a hungry flock of sheep can train humans to stay alert, says Bennett.
"You're just going out there daily," she says. "That's probably the biggest advantage."