Mite Threatens $30-Million Avocado Crop

An avocado-destroying mite that has caused extensive crop damage in San Diego County is spreading to groves in Ventura County, the No. 2 avocado-producing region in the state behind San Diego, officials said Monday.

The voracious mite was found on avocado trees in Moorpark and Somis within the last two weeks, raising fears that Ventura County, which sold nearly $30 million in avocados last year, could also be facing widespread infestation if it fails to take control of the problem early.

At this point, “there hasn’t been any real crop damage,” said Ben Faber, the county’s farm adviser with the University of California. “That’s why it’s so critical that we nip this in the bud now, because once it starts and spreads around it’s almost impossible to control.”

Faber said the microscopic mite also has migrated to groves in Riverside, just north of San Diego, and more recently in Goleta in Santa Barbara County.

Agricultural officials in Ventura County said steps are being taken to combat the mite but admit it is an uphill battle. They point out that nearly every grove in San Diego has been infested over the last three years.

“There’s very little you can do with this type of pest as far as preventing its spread,” said David Buettner, the county’s deputy agricultural commissioner. “We expect it to grow very rapidly.”

The Olygonichus perseae mite attacks the underside of avocado leaves, draining them of chlorophyll. Once the leaves are dead, the fruit is left unprotected from the sun and eventually withers and drops to the ground.

Faber said the biggest problem in combatting the mite is that it protects itself under leaves by spinning a thick web that acts as a barrier, under which the mite lays its eggs. Dave Machlitt, a pest-control consultant who discovered the mite in Moorpark and Somis avocado groves, said he recently sprayed the Moorpark trees with a specially refined, nontoxic petroleum-based oil that covers the leaf and suffocates the mite. He is planning a similar treatment in Somis.

About 40 trees had been attacked by the mite in Moorpark, Machlitt said, and between 15 and 20 in Somis. Spraying is not normally done on avocado trees, he noted, because the process is expensive, difficult and presents the risk of killing beneficial insects.

He said once he has completed the spraying, he plans to follow the course of Riverside and San Diego farmers and release thousands of “predator” mites. The laboratory-bred Galendromus helveolus mite is a natural enemy of the perseae .

But waging biological warfare on the perseae mite is expensive and the demand for the predator already far exceeds the supply, said Guy Witney, a farm adviser in Riverside County.

Generally, 1,000 predator mites cost about $15. For the strategy to be effective, a grower would have to release 5,000 to 10,000 mites per acre. Moreover, because the predator moves so slowly from one tree to another, it could be two or three years before it effectively reduces the population of the avocado mite.

“It’s that two-year period that we’re really worried about in Ventura County,” said Rob Brokaw, owner of Brokaw Nursery in Santa Paula, which supplies avocado trees to growers. “The distressing thing about it is that the mite really comes through like a steamroller.”

Brokaw said he has shown his crews photographs of the mite’s web to help them keep watch for it. An infestation would be very hard on avocado farmers, who have already suffered through a freeze and still contend with high water prices and decreasing sales due to overproduction, he said.

A large infestation, Brokaw added, “would be a triple whammy.”

Rex Laird, executive director of the Ventura County Farm Bureau, expressed similar worries. Avocados, grown locally on more than 16,000 acres, are the sixth-largest money crop in Ventura County.

“How fast can it spread? I don’t know,” Laird said. “But if it spreads and goes clear across the county, this could be very significant. It’s something we’re very concerned about.”

Laird said Machlitt is preparing a report on his work in Moorpark and Somis to be presented to growers and agricultural officials Sept. 23 during a special meeting at the Ventura County Government Center.

Witney and Faber said that one advantage Ventura and Santa Barbara counties may have over Riverside and San Diego is that the areas have more rainfall and cooler temperatures. The avocado mite, which is believed to have migrated to the United States from Peru or Mexico in 1990, may not be so tolerant of such conditions.

“It did take a lot of time for the mite to move from San Diego to Riverside County,” Witney said. “But whether it’s limited to how far north it can go, we don’t know.”

Agricultural officials said the mite could be spread by the wind or by attaching itself to farming equipment and the clothes or picking bags of fieldworkers. The mite also clings to fruit crates, which are transported to different areas.

Extra sanitary measures and ensuring that equipment is clean could reduce the spread of the pest, officials said.

“The better sanitation you have, the better control you have,” Buettner said. “But I don’t expect it to be too long before it spreads around to other avocado areas.”

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