Ash Whitefly Is Conquered, Agriculture Officials Declare

Even as a new California pest devastates vegetable and fruit crops in the Imperial Valley, University of California agriculture officials in Ventura County are declaring victory over its pesky cousin, the ash whitefly.

Agriculture officials said Friday they have seen no sign of the fast-moving poinsettia whitefly, which in recent months has become the Imperial Valley’s worst natural pest, according to some growers in the desert region. They say they are not concerned for now because the poinsettia whitefly, a newcomer to California, is still more than 200 miles from Ventura County.

But they pointed out that the new pest could eventually make its way to the county’s vegetable crops.

“It’s just like with any other pest,” said David Buettner, chief deputy agricultural commissioner in Ventura County. “All you can do is hope you don’t get it.”

Meanwhile, agriculture officials said they believe that the ash whitefly, which arrived in the county about three years ago, is nearly eradicated. The pesky ash whitefly terrorized east county homeowners by dripping excrement onto cars and patios. More important, it threatened to damage the county’s valuable citrus crop.

Thanks to a 16-month-old program releasing tiny predator wasps, the ash whitefly has been 90% eradicated in Ventura County, said Jim Downer, farm adviser with the University of California agriculture extension office in Ventura County.

The wasps, no bigger than a speck of ground pepper, seek out the immature whitefly larvae, or nymphs, which attach themselves to the backs of leaves and plants. The wasps sting the developing insects and lay eggs inside their bodies.

“Their goal in life is to find whitefly nymphs,” Downer said. The wasps “have established themselves in the county,” he said, “and I firmly believe that the whitefly problem is behind us now.”

Buettner, however, is less optimistic. He said there may still be areas of the county where the ash whitefly is entrenched.

The ash whitefly, a tiny mothlike creature, was discovered near Simi Valley and Thousands Oaks in 1988 after it moved in from Los Angeles County. It quickly spread throughout Ventura County.

True to its name, the ash whitefly attacks ash and other large shade trees, but it also feeds on the native California chaparral that is common on hillsides in the eastern part of the county.

Homeowners in Agoura Hills and other east county cities complained when the whiteflies swarmed around them after an infested tree was disturbed. But the whiteflies were even more distressing in their larval stage, when the sap-sucking, immature insects produce their sticky white excrement, known as honey dew, that drips onto outdoor furniture, cars and sidewalks.

“It was a serious problem because there were no natural enemies in this county,” Buettner said. “In areas where there were a lot of ash or ornamental pear trees, people were upset because they were dropping honey dew all over their Ferraris.”

The threat to the citrus crop never materialized, as the whiteflies had enough other vegetation to keep them happy until the wasps established themselves, officials said.

The state of California and the University of California began releasing the predator wasps last July at four locations in Camarillo and the eastern half of the county. The city of Ventura also purchased and released 500 wasps, at $1 each. And Downer released another 250 in the Ojai area.

The wasps are established in several areas of the county now, but state officials are still working on ways to help the population multiply and spread throughout the county, Buettner said. Spraying pesticides is ineffective against the whiteflies, he said.

Rincon-Vitova Insectaries, an insect breeding company in east Ventura, has begun working on ways to breed the wasps so more can be offered for sale next spring, said John Rodgers, an entomologist at the facility.

“We’ve got a waiting list for them once we get them going,” he said. “Mostly the people who want them are homeowners with large ash trees.”

Buettner said he had no estimate of damage caused by the ash whitefly, which can slow plant growth and kill young plants.

“It’s basically just a nuisance at this point,” Buettner said. “It hasn’t affected any of the commercial crops, except a small amount of nursery crops.”

Yet another pest, known as the greenhouse whitefly, is becoming a nuisance to plants and trees grown in nurseries, said Robert Brokaw, whose family owns the Brokaw Nursery of Saticoy.

“They are real tough to deal with,” he said. “They like the warm humidity inside the greenhouse, and there is lots of food in there.” He said it is too early to say whether the greenhouse whitefly will become a major problem.

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