Growers Battle Infestation of the Whitefly

Deep in the trenches of the Oxnard Plain, strawberry grower Cecil Martinez is waging a war, unleashing an army of wasps and unfurling a giant no-pest strip to rid his ripening crop of a new menace.

The enemy is silent and small, a white-winged fly no bigger than a grain of rice. But the tiny pest poses a formidable threat, having descended on Martinez’s 88-acre ranch in heavy numbers to feast on the fruit as it matures from pale green to fire engine red.

To demonstrate the extent of the infestation, the 59-year-old rancher grabs hold of a strawberry plant and gives it a shake, stirring a cloud of fluttering white flies like a man shaking up a blizzard in a snow globe.

“I’ve never seen them this bad before,” said Martinez, two decades of farming experience adding weight to his words. “We’ve been through a lot of battles, but this is a whole new world for us. I’m trying every little trick I know but so far they’re still here.”

At a time when Ventura County strawberry growers are preparing to harvest a record number of acres, Martinez and a handful of other farmers are battling an unprecedented invasion by the greenhouse whitefly, the latest threat to the county’s second-most-valuable cash crop.

With nearly 6,700 acres in production this season, the county has firmly established itself as California’s second-largest strawberry growing region, trailing only the Watsonville-Salinas area in production and crop value.

The acreage represents a 15% increase over last year and a more than 50% jump since 1994, when 4,449 acres were dedicated to strawberry production. In fact, no area of the state has added more strawberry fields in recent years.

“I think it says that more and more people are buying strawberries, that they have confidence in our fruit and they think it’s good for them,” said George Yamamoto, an Oxnard grower who doubles as chairman of the California Strawberry Commission. “All of that seems to be working in our favor.”

Such increased activity, however, could inadvertently be contributing to the whitefly’s population explosion in the local strawberry crop.

Most of the new acreage is being farmed by growers who are planting strawberries in the summer for harvest in the fall, Yamamoto said. Normally, strawberries are planted in the fall and harvested between late December and mid-July. The new emphasis on summer plantings has allowed growers to reach out to new markets to meet early-season demands, Yamamoto said.

But researchers are trying to determine whether such off-cycle activity has also given rise to whitefly populations, providing the pest with a new source of food and a new place to propagate.

Summer Plants May Have Drawn Pests

Although other crops--including cucumbers, tomatoes, beans and squash--have long faced some whitefly damage, the insect had never been a major problem for strawberry growers anywhere in the state.

But last year, a local grower encountered a heavy infestation on about 150 acres of summer-planted strawberries in two fields along Hueneme Road east of Oxnard.

Those plants were in the ground months after the spring and summer strawberry harvests had ended and after other crops in surrounding fields had been picked and plowed under. With no other food source available, researchers believe the whitefly may have settled in the early season strawberry crop as it searched for a new home.

“We’re trying to determine what effect the summer planting has had on the whitefly,” said Frank Westerlund, the strawberry commission’s director of research. “Right now we don’t have any evidence to show that there’s a link, but there’s definitely an association we want to pursue.”

The infestation is not the sort of problem that can wipe out the strawberry crop. Rather, in large enough numbers the pest can reduce the yield from a particular field and render the crop less valuable.

As the pests grow from the nymph stage to adults, they attach themselves to the underside of strawberry leaves, piercing them with their mouths and literally sucking the life out of the plants, resulting in undersized fruit. In addition, the insects secrete a black sooty mold, called honeydew, that mars the fruit with ugly black blotches and makes it less marketable.

Pesticide Came Too Late for Some

While other strawberry-growing regions across the state have reported some whitefly activity, Ventura County has experienced the largest and most significant problem to date. From the original 150-acre infestation, the pests now have been reported on more than 600 acres of berries on the Oxnard Plain.

To beat back the invasion, Ventura County growers last year won an emergency exemption from state and federal regulators to apply a chemical--known by the brand name of Admire--on the upcoming strawberry crop.

The pesticide has been approved since 1994 for use on such crops as lettuce and cantaloupes, but was not registered for application on strawberries. The chemical is applied through drip irrigation systems and taken up by the roots of the plants. The insects die by ingesting the chemical as they feed.

“We were fortunate that we were able to get the registration on Admire,” said Yamamoto, who applied the chemical to his 70-acre strawberry crop late last year after noticing the pest on his property. “It was enough of a concern that we felt we really had to stay on top of it.”

The emergency registration came too late, however, for the crop planted last summer by Reiter Bros. Inc., one of the largest strawberry growers on the Oxnard Plain.

The Oxnard grower was at ground zero of the initial infestation, farming the two fields where the whitefly hit hardest. As a result, the fall harvest from those fields yielded half the normal amount and the fruit was of second-grade quality, said Gerry Robertson, the company’s operations manager.

“Basically we just made enough to break even,” said Robertson, adding that he was able to use Admire on the company’s fall planting. “We are obviously concerned about it but we’re hoping this Admire is going to be at least one tool for us to use in the future.”

Researchers say there could be plenty of reasons, other than the summer-planted crop, to explain why the pest has descended on local strawberry fields. An unusually humid summer is thought to be partly responsible for the population explosion of this particular whitefly species, which is more commonly found in the warm environment of greenhouses.

Joint Efforts May Quell Spread

And increased urbanization and the failure of growers of other crops to properly control whitefly populations could also be contributing to the spread.

Whatever the reasons, agricultural officials say it’s essential for growers across the county and the state to keep an eye on the problem and figure out ways to work together to combat the pests.

As that effort unfolds, Cecil Martinez has come up with a strategy of his own.

His ranch is sandwiched between the two fields that experienced the heaviest infestation, in the flight path of the white-winged pests as they took to the air after surrounding crops were harvested.

His place is like a war zone as he tries to hold the line. In addition to the fly problem, there is the shrieking of fireworks and booming of cherry bombs to scare away gulls and blackbirds.

He also used Admire months ago and so far the pesticide seems to be doing a good job of killing off the whitefly larvae. He unleashed some parasitic wasps to attack the adults and last week encircled his farm with a large yellow tarp, smearing it with petroleum jelly so the bugs will stick, after learning that the insect is supposed to be attracted to that color.

He’s hoping that last week’s rain will drown out the adults or, at the very least, shoo them away. Absent that, he intends to load up his tractor’s spray rig with a soap-and-oil solution to wash the pests from his crop.

The stakes are high. The strawberry crop is his sole source of income, a fickle money-maker that sustains him and his family all year long. But he’s also been farming long enough to know that this newest threat is part of a larger game, that for better or worse he is part of an industry where the demands change as often as the seasons.

“Farming is a constant challenge--you put all this money into the ground and you’ve got to keep working it to get a return on your investment,” he said. “The one thing I know is that I’m not in control of any of this; I have to leave it to the man upstairs. I guess you might say it’s a roll of the dice, but I’ll stay out here day and night if I have to so I can grow these things and get them to market.”

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With nearly 6,700 acres of strawberries in production this season, Ventura County has solidified its position as California’s second-largest strawberry-growing region, trailing only the Watsonville-Salinas area. The acreage represents a 15% increase over last year and a more than 50% jump since 1994.

Acreage of Strawberry Fields

1994: 4,449

1999: 6,692

Greenhouse Whitefly

(Trialeurodes vaporariorum)

Size: Less than one-eigth inch in length.

Diet: Plant sap

Development from egg to adult: As little as 18 days, depending on temperatures and host plant.

* Eggs of whiteflies are laid on the undersides of leaves. a female can lay more than 300 eggs.