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Giant Whitefly Update

June 14, 1998|ROBERT SMAUS | TIMES GARDEN EDITOR

The giant whitefly is continuing its spread into Southern California from its native Mexico, puzzling gardeners who encounter this messy pest for the first time.

San Diegans know it well, because this whitefly was discovered there in late 1992. Last year, we reported that it was in Orange County, and this year we are getting calls from West Los Angeles and the Eastside.

Though it is not spreading as fast as the ash whitefly did several years ago, pockets have been found as far north as San Luis Obispo County.

The giant whitefly isn't much larger than the ash whitefly (it's about three-sixteenths of an inch long), but makes a much bigger mess, covering leaves of plants with white waxy deposits and dripping masses of waxy filaments that look like white beards.

Black sooty moot fungus quickly follows, living on the whiteflies' excrement.

The whitefly dines on a long list of plants--from acacia to xylosma--but favors red-flowered hibiscus (it prefers reds over yellows for some reason), giant bird of paradise, orchid tree, banana, mulberry and xylosma.

It can also be found on bougainvillea, some citrus, canna, eucalyptus, ficus, fuchsia, liquidambar, nandina, pittosporum, solanum and water lilies.

This sizable list of host plants is one reason the state is working to find a permanent biological control for this pest.

Two parasitic wasps have been imported from Mexico and released in small numbers in several areas, but their effectiveness won't be known until this fall. It is suspected that one or both may eventually bring this whitefly under control.

In the meantime, it pays to keep careful watch on the garden because this pest is fairly easy to control if you act fast.

Colonies tend not to fly or wander around (they drift into your garden on the wind) and cluster on the undersides of leaves. Simply picking off the leaves, putting them in a plastic bag and sending them to the dump will often eliminate the whiteflies.

If they have already become too numerous for that simple technique, the best control is to simply blast them off the foliage with a strong stream of water.

University of California tests have shown that this works just as well as chemical treatments, and spraying with poisons may kill off beneficial insects that are helping to control the whitefly population.

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