A fast-moving insect from the Mediterranean, first found in North America in a Van Nuys yard July 18, is threatening trees and pestering homeowners in a wide swath of Los Angeles County.
The ash whitefly weakens trees by sucking sap from the undersides of leaves. The leaves on many fruit and other trees will turn downward and fall off early. Also, a sugary “honeydew” secreted by the tiny, white pests draws ants and leads to formation of a mold that further attacks the trees.
“It’s a mess,” said Bob Atkins, deputy Agriculture Commissioner for Los Angeles County. “We’re getting lots of calls.”
Atkins said scientists do not have a clue how to deal with the ash whitefly, which breeds in southern Europe and northern Africa, and was probably brought to Southern California on a plant.
It has spread rapidly because it has no natural enemies here, he said. It also resists insecticides and eradication efforts similar to those used against the Mediterranean fruit fly, a pest that posed a much different problem for scientists.
The first ash whiteflies were reported by a homeowner in Van Nuys in the middle of the San Fernando Valley. Inspectors quickly found more in Glendale and the Hollywood Hills.
“In no time at all we found it right outside our door here in El Monte,” Atkins said Tuesday.
The whiteflies have been found on trees from the olive, rose and legume families--a large grouping that includes ash, pear, apple, persimmon, peach, nectarine, apricot, plum and other trees. Both the fruit-bearing and ornamental kind can become infested, Atkins said.
Nurseries face the greatest threat of economic harm. State agriculture officials have issued an alert advising that certain trees should not be shipped out of Los Angeles. Citrus trees resist infestation, a turn of fortune that will lessen the threat to farmers in Ventura County and other nearby citrus areas.
Resemble Tiny Moths
For homeowners the nuisance may first be seen as swarms of thousands, perhaps millions, of adult whiteflies that Atkins said resemble tiny moths. The swarms, which can look like a fine ash blowing in the wind, have prompted many of the calls, he said.
Most damage comes from the juvenile stage, which can be seen as a waxy kernel attached to the underside of leaves. The young suck the tree’s sap, weakening the tree to other pests and diseases. The “sooty mold” that forms can also damage the trees.
Because the young feed on sap, any chemical treatment must be taken into the plant and sent to the leaves through the tree’s vascular system. But on trees that bear fruit, the treatment will also taint the fruit, Atkins said.
Eradication was effective with the Mediterranean fruit fly because they were lured to a sweet bait laced with the pesticide malathion. The bait could be sprayed on large areas from aircraft.
Atkins said the ash whitefly must be attacked tree by tree, but the infestation is already so widespread that it would prove too costly. Early tests with insecticides have not done much to stop the pest, Atkins said.
UC’s Aid Sought
Agriculture officials have asked the University of California for help in investigating if there is a natural predator or parasite that will combat the whiteflies. The UC assistance may involve sending scientists to the Mediterranean to see if there is a wasp or other natural enemy that could be introduced in Southern California, Atkins said.
The infestation is typical of what can go wrong when a new pest is brought into an area where it has no natural obstacles to spreading, Atkins said. Now that they are going, the whiteflies may not stop until they run out of food, he said.