Ash Whitefly Stirs Fear for Next Year’s Farm Crops

The ash whitefly, which has plagued Southern California for the last year and has moved northward to the San Joaquin Valley, poses no serious threat to crops this year, but its effects could be serious in the next harvest season, agriculture officials say.

Because the whitefly moved north so late in the growing season, the pest has not done any serious damage to trees in the valley yet.

“What will happen next year is our biggest concern right now,” Norm Smith, an entomologist for Fresno County, said Monday.

He said most of the whiteflies found in Fresno County so far have been in non-growing areas.

“But it could be a real problem if it gets into growing areas,” Smith said, “and there is not much to stop that from happening.”

The sap-sucking pest is immune to most pesticides and has no natural enemies in California, said Dick Rice, an entomologist at UC Davis who is working at an experimental field station in Fresno County.

“The whitefly could seriously damage such crops as olives, peaches, pears, plums and citrus,” Rice said. “You’re looking at damage in the hundreds of thousands of dollars in the valley if it gets into those crops.”

The whitefly, a native of Europe, the Mideast and North Africa, was first spotted in Van Nuys in July, 1988, and spread rapidly throughout Southern California, feeding mainly on suburban ash, ornamental pear and pomegranate trees.

Although they are known as whiteflies, the insects are not true flies but are related to aphids and other sucking insects.

They feed on the underside of leaves, eventually deleafing trees and cutting a tree’s production of fruit.

Scientists at the University of California are working with two of the whiteflies’ natural enemies, tiny stingerless wasps and a variety of ladybugs, imported from Italy and Israel.

But Rice said it could take several years to establish sufficient populations of the wasps and ladybugs to produce a significant effect on the whitefly population.

Agricultural officials know that the whitefly has spread as far north as Fresno, but Smith said it could have moved even farther northward in the state.

“We don’t have a formal detection program in place further north than Fresno County, so it is possible the insect has moved into areas north of Fresno County,” Smith said.