Little Bug a Big Worry for Growers of Avocado Trees

It’s the last thing growers needed: a destructive little bug that spreads rapidly among groves as it sucks the life out of what were once highly profitable avocado trees.

And, because this critter is a newcomer to San Diego County--and the United States, for that matter--scientists know little about its life cycle or how to combat it.

Already hard-pressed to squeeze a profit out of their fruit as water prices continue to rise, many avocado growers must now dig deeper into their pockets to pay for chemical sprays or biological controls to combat their new enemy, the avocado mite, which growers say is perhaps their most formidable insect foe ever.

To date, the avocado mites have been found on about 10,000 acres, roughly a third of all avocado acreage in San Diego County, agricultural officials say.

“Countywide it hasn’t done a lot of damage yet, but it certainly has the potential to be very destructive,” said one pest management adviser in the northern part of the county.

Rick Opel, vice president and farm manager for Henry Avocado Co. in Escondido, which manages about 2,000 acres, said: “I’ve got some really productive groves that have just been knocked out of production by this mite. I’d say that, economically, it’s severely affected about 100 of our acres.”

Though they have on rare occasion been seen on the leaves of weeds and peach trees, the avocado mites savor avocado leaves, which they kill by sucking out the chlorophyll. That causes yellowish spots to form on the leaves, which eventually drop off the tree and expose the fruit to harmful sun rays.

In the worst-case scenario, the fruit gets sunburned and drops prematurely; the tree is weakened and may produce less fruit next season.

There has been no official effort to assess the economic impact of the mite so far. And, because so little is known about it, agricultural experts are not willing to estimate a dollar cost for next year, when mite populations will be significantly higher.

“We’re considering it a serious pest, but we don’t know how devastating it can be, and we don’t at this time have a chemical to adequately control it,” said Bill Snodgrass, the county’s assistant agricultural commissioner. “It’s just about anybody’s guess on what the economic impact might be.”

Populations of the avocado mite, which is believed to originate in Mexico or Central America, exploded this spring in southern Escondido and devastated some areas there, while severely cutting productivity in others, according to grove manager Steve Olson of Olson Avocado Management in Escondido.

The mite is found in groves as far north as south Riverside County, officials say.

Some growers are pinning their hopes on a predator mite. That mite has, in an experiment in an Escondido avocado grove, fed on the avocado mite and kept its population there under control. It is now being studied in a laboratory.

“Until a few weeks ago we didn’t know what to do, but this beneficial (predator) is really helping the situation,” said Avi Crane, vice president of the California Avocado Commission.