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Creating habitat to attract such natural predators of pests as birds, foxes, coyotes and bats could be a double blessing for viticulturists: harnessing powerful pest control allies while saving and restoring some of what is most precious of rural California environments.
"Birds are insect predators that work from dawn until dusk in the vineyard canopy, looking for food to give their young," says David Graves, co-owner of Saintsbury Winery in the Carneros District, located in the southern regions of Napa and Sonoma counties.
Graves is known as the "Bird Man of Carneros" because he is dedicated to introducing bird boxes into every vineyard in Sonoma and Napa counties. So far 125 new bird boxes, built to encourage insect-eating tree swallows, bluebirds and wrens to move in, have been erected in several vineyards.
The Buena Vista Winery set out 15 of the bird boxes last year. "We had an 80% occupancy rate in our bird boxes. The bird population in Carneros has increased immensely, which is wonderful," according to Anna Moller-Racke, vineyard manager for the winery.
The boxes were designed by Donald Yoder of the California Bluebird Recovery Program, who says: "Birds are great pest catchers and certainly a lot more economical than buying pesticides and poisons. Pesticides have killed off the natural pest control system in vineyards and other agricultural operations, but farmers are now seeing the benefits of restoring these natural predators."
Fifty of the bird boxes were constructed by boys at the Hanna Boys Center, and a bird club at Los Carneros School is helping set up the boxes and monitor nest activity.
Another way to avoid using chemicals is by using specific cover crops. Through this method the vegetation combats erosion and reduces or eliminates the need for herbicides. A surprising side-effect has been noticed by many growers: cover crops provide habitat for beneficial insects such as spiders that eat insects. On the down side, though, gopher, rabbit and other rodent populations often rise when their underground tunnels are no longer disturbed by annual disking.
To cope with rodents and replace the extremely toxic, environmentally persistent rodenticide diphacinone -- which is heavily used in both Sonoma and Napa counties -- grape growers such as Keith Kunde of Sonoma Valley's Kunde Winery are putting up owl boxes in their vineyards.
"A family of owls can eat up to eight gophers a night," notes Kunde. Barn owls don't construct nests, roosting in existing shelters instead. But nesting boxes must be specially designed to avoid becoming shelters for pest birds such as starlings. With an average of 1,000 rabbits and gophers to their credit a year, an owl family can be a valuable asset worthy of a customized home.
Kunde is joined in his enthusiasm for owls by Mondavi viticulturist Michael Klug. "Gophers are a big problem here. We trapped 2,500 of them last year. Hawks and owls eat a lot of gophers," says Klug, who has set special perches throughout Mondavi vineyards and constructed nesting boxes for screech owls, also big fans of rodent dinners.
Klug says he now plants willow trees in boggy areas of the company's land in Napa County to create habitat attractive to natural predators such as songbirds. He also plans to plant patches of native oaks, willows and buckeye as a means of combating rabbits.
"Coyotes, foxes and bobcats are jackrabbit predators, but they need cover to hide in, and cover is scarce in the Carneros. So we have to provide it for them," says Klug.
Birdman Dave Graves also likes bats for insect control. Graves notes that "These days, we're facing a lot of insect-borne vine maladies like Pierce's disease. When you encourage insectivores like bats and native songbirds in your vineyards, you reduce pest pressure on the grapes."
He commissioned Petaluma wildlife biologist Greg Tatarian, who specializes in the behavior of bats and birds of prey, to build homes for pallid bats, a rare big-eared eater of ground pests such as Jerusalem crickets. Other native bats such as the California Myotis, Yuma Myotis, Mexican free-tail and big brown bat eat leafhoppers, beetles and other insects.
Ironically, all bat species are in serious decline, at least in part because of pesticides. Patricia Winters of the Bat Conservation Fund reports that "In Carlsbad Caverns, 90 percent of the bats are gone -- they're down to 217,000 from a high of 11 million. Tissue tests done on the Carlsbad survivors show very high levels of pesticides."
It seems fitting that bats should be an integral part of programs designed to eliminate the need for pesticides.
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