Ash whiteflies have been found at two sites in San Diego County, and an expected infestation within a year or two could have a devastating effect on the county’s $250-million flower and ornamental tree business, the county’s top agricultural official said.
“We know it will get here, it’s a matter of what will we do when it gets here,” San Diego County Agricultural Commissioner Kathleen Thuner said.
She said the insect could also damage the county’s $57-million citrus crop. “Some estimates are as high as 20% of the crop being lost to commercial production” in one year, she said.
Experts at Odds
However, experts differ on whether the ash whitefly will make its home in citrus trees. Tom Bellows, associate professor of entomology at UC Riverside, said crops most widely damaged in Europe by the ash whitefly, scientifically known as Siphoninus phillyeae , did not include citrus trees. Other entomologists note that the pest has not successfully laid eggs on citrus. But Thuner said it had attacked citrus in Syria and could attack them here.
Nonetheless, the bug, which weakens dozens of types of fruit trees by sucking on their leaves, is feared because it has no natural enemies in California and is not susceptible to pesticides.
Unlike the Mediterranean fruit fly, which is susceptible to pesticides, there is no way to trap ash whiteflies. “The medfly is attracted to a lure, a feeding substance, but the ash whitefly, so far as we know, does not particularly go to anything,” said Ray Gill, a state Department of Food and Agriculture entomologist. Pesticide sprays are ineffective because infestation in Los Angeles is so large and because the insect sticks to the underside of leaves, where they are protected from sprays.
Found in Van Nuys
Discovered in Van Nuys last July, the ash whitefly has spread throughout the San Fernando and San Gabriel valleys and has been spotted in Beverly Hills, authorities said. Experts were at first stumped because the ash whitefly had never been encountered in the United States.
San Diego County entomologist David Kellum said that, although there is still no infestation in San Diego, one is likely within a year or two. “It could be quite devastating,” he said, because the ash whitefly produces a lot of honey dew and waxy material, which makes it hard for pesticides to get through to the insect.
The ash whiteflies found in San Diego were discovered on ash and pear trees in two nurseries, one in Chula Vista and one in Jamul, in November. In January, a few more flies were found in the same nursery in Chula Vista. Kellum said the plants had been disposed of and the flies sent to Sacramento for analysis by the state Department of Food and Agriculture.
No other occurrences of the ash whitefly have been found in San Diego County, he said.
The flies feed on peach, pear, apple, apricot, pomegranate, olive and plum trees, Kellum said. Leaves on afflicted trees curl, turn yellow and drop prematurely.
“If other states or counties decide they don’t want it and establish quarantines against it,” Bellows said, San Diego nurseries’ ornamental tree crops could be hurt.
The pest secretes a sticky substance as it sucks the juices out of a plant’s leaves. This substance attracts ants and grows mold, making the fruit inedible and ornamental plants meant for commercial sale unattractive. The substance also drips onto cars parked beneath trees and the pests themselves are so small and so numerous that people find themselves inhaling them, Bellows said.
Gill said some of the flies may have escaped from the San Diego nurseries before they were detected. And it’s possible that anyone driving from Los Angeles with a few in the car could spread the infestation, he said. “We don’t know how far they’re carried on the wind.” Gill added.
Scientists trying to biologically control the pest are looking for other insects that feed on the ash whitefly, but lack research funds. “The problem is that, when we bring in a natural enemy, we have to bring it in under quarantine and conduct exhaustive tests on it to make sure it in itself won’t become a pest,” Gill said, adding that getting the pest to breed under quarantine is time-consuming and costly.
“We’re under the impression it would take $30,000 to initiate a biological control program for a single test,” Thuner, the agricultural commissioner, said.
The Los Angeles County Board of Supervisors has committed $10,000 for such a program. Thuner said her department had asked the San Diego County Board of Supervisors for $2,500 as a budget item for such research, but the funds have not yet been approved.
“At the best, we’re looking at three years before we’ll have something available for controlling the pest. The longer we wait, the worse it’ll be,” Thuner said.
40 Native Species
Of 50 to 60 species of whiteflies in California, 40 are native. But about 20 are introduced from other parts of the world, and half of these are “serious problem from time to time” because their natural enemies, such as beetles and parasitic wasps, were not imported with them, Gill said.
Authorities do not know how the ash whitefly was introduced to Los Angeles but suspect it was brought into the country on uninspected contraband plants.
Thuner suggested that homeowners keep their trees clean, trim them so that their branches do not touch the ground, and watch for ants.