GARDEN FANATIC: Giant Whitefly return to Laguna

Last week, while walking the neighborhood with Catharine, Buster and Blondie, scores of giant whitefly whizzed by our heads. Several times larger than the common whitefly, these unwelcome pests have returned to Laguna and other locales, threatening many species of plants. The recent warmer and humid weather has encouraged the population of giant whitefly to swell in numbers.

Hibiscus was originally the host of choice, but the giant whitefly now attacks a number of plants — a reported 39 genera at the beginning of summer. Known Laguna hosts include bird of paradise, citrus, fuchsia, morning glory, salvia, schefflera and xylosma.

The giant whitefly eggs, larvae and adults form dense colonies on the undersides of leaves — trademark beardlike threads up to four inches long hang from infested leaves. Because the insects are actively secreting honeydew, sticky strands of material become a nuisance, along with the black sooty mold that grows on the excretions.

The giant whitefly is resistant to chemical treatment, so those who believe in elimination through the use of stronger pesticides will discover that this is not an effective option. The proverbial pesticidal fly swatter will simply not permanently eliminate giant whitefly from the landscape.

Many gardeners have discovered that washing off the undersides of foliage with water can reduce infestations. Although this is my favored control, it is fair to say that there are limitations. Even with the most focused attention to forceful spraying, water will only remove a portion of the whiteflies and provides no residual activity.

I find that infested plants must be washed once or twice (or more) a week to keep whitefly populations from increasing.

If you don’t have time to wash your plants everyday, both insecticidal soaps and horticultural oils will kill adult whiteflies and immature larvae through suffocation... although they are not particularly effective against eggs and mature larvae. Because these chemicals have little residual activity, they are not as harmful to beneficial insects as stronger and more persistent pesticides; however, they must be applied weekly for control.

We heard Oliver’s insistent mewing as we made our way home. He greeted us with a nod of his head and then raised his paw in the opposite direction. He had caught his first catnip mouse in years! I picked up our cat and thought grimly, I hope he learns to catch whitefly next. See you next time.

STEVE KAWARATANI is married to writer, Catharine Cooper, and has one cat and four dogs. He can be reached at (949) 497-8168, or e-mail to plantman2@mac.com.