Pheromones Are In The Air by Stuart Leavenworth, Bee Staff Writer

Walnut growers hope synthetic fog throws off moth's mating.

MARYSVILLE - Every spring, Mike Bennet's walnut groves become ripe with the smell of love.

Tiny moths emerge from their cocoons, then use the scent of other moths to locate mates. Within weeks, millions of these codling moths are flying through his orchards, ready to bore through his walnuts and destroy another year's crop.

Now, in their ongoing battle against bugs, Central Valley farmers are using the sexual habits of insects as a weapon against them. More and more, they spray pheromones – chemicals emitted by all creatures to attract mates – to fog orchards with a confusing cloud of sexual scents and make it more difficult for pests to reproduce.

It's an experimental technique but one that holds great promise. That's good news for California's orchard industry, which faces increasing restrictions on its favored pesticides, cultural advisers.

"This is not a fix-all, but it should dramatically reduce the chemicals we spray," said Patrick Weddle, a Davis agricultural adviser who is working with Bennett and other farmers.

In particular, the use of pheromones could cut down on applications of three toxic pesticides – azinphos methyl, chlorpyrifos, and diazinon – that regularly are sprayed on walnuts.

All three chemicals have been known to wash into local waterways, including the Sacramento River, which provides drinking water for Sacramento and many other cities. The compounds also pose risks to farm workers and children who regularly consume fruit, according to the U.S. Environmental Protection Agency.

With pheromones, on the other hand, the only real risk is dousing yourself in the spray and becoming a magnet for amorous insects.

"You don't want to go to the butterfly exhibit for a while," joked Bennett as he walked through one of his groves the other day.

On Wednesday, crews sprayed a cloud of codling-moth pheromone through more than 150 acres of walnut groves north of Marysville. The groves are owned by Deseret Farms, a major walnut grower that employs Bennett and is participating in a project to perfect use of "mating disruption techniques."

The project, organized by the nonprofit Center for Agricultural Partnerships, involves 1,000 acres of commercial walnut groves in the Central Valley. Over the next two years, officials with the group hope to expand that to 25,000 acres, or an eighth of all walnut acreage in the state.

California farmers, who produce 99 percent of the nation's walnuts, are watching closely. When left uncontrolled, codling moths can destroy about 40 percent of a crop, mainly by boring into the nuts and leaving them susceptible to rot.

"Codling moths are the proverbial worm in the apple," said Larry Elworth, executive director of the Center and a former apple grower. "They pose problems for all kinds of fruit growers, all over the country."

Elworth said pheromone disruption holds lots of potential. The trick, he said, is getting farmers involved and figuring out techniques that work in the field, not just the lab.

Three years ago, for instance, walnut growers and various state agencies experimented with a parasitic wasp to kill moths. "Unfortunately," said Weddle, "the amount of parasite necessary to do the job made the costs prohibitive."

By contrast, tests have proven pheromones to be effective and reasonably-priced, said Weddle. The pheromone technique costs about a third more than using pesticides, but costs are expected to drop as the spray becomes more available, he said.

As Weddle notes, spraying pheromones isn't as simple as wafting a cloud through an orchard. The spraying, he said, has to coincide with the peak mating period of the moths.

To get the timing right, Weddle and another crop consultant, John Post, are using two types of baited traps. One contains moth pheromone, which provides ~ indication of the males that are mating. The other includes a type of pear scent, which attracts moths of both sexes.

Once a sufficient number of moths show up in the traps, farmers can crank up their spray trucks and pump the pheromone into the orchards, just like they would a pesticide.

"We are not sure if the males get lost or just get desensitized," said Weddle. But it works, he added, reducing reproduction by 60 percent to 70 percent.

Over the next year, the agricultural partnerships group and various walnut growers hope to fine-tune the methodology so it can be used across the Valley. Funding for the $200,000 program comes from the partnerships group, the federal EPA, 3M Canada (which makes the synthetic pheromone spray), and the Great Valley Center, another nonprofit group.

Bennett said it makes sense for growers to try alternatives, and that he's tired of headlines about farmers polluting water.

"We are sensitive to that," said Bennett. "We want to help the industry in any way we can."

The Bee's Stuart Leavenworth can be reached at (916) 321-1185 or