Attacking the giant whitefly population

The giant whitefly has returned this summer. It is a winged insect found mainly on the undersides of leaves. The recent warmer temperatures has encouraged the population to swell, sending gardeners to their favorite nursery for relief.

Hibiscus was originally the host of choice, but the giant whitefly now attacks a reported 39 genera. Known Laguna hosts include bird of paradise, citrus, fuchsia, morning glory, salvia, schefflera and xylosma. Female whiteflies lay their eggs in a characteristic circular pattern on the undersides of leaves. The larvae insert their mouthparts to remove sap from leaves, weakening plants.

The eggs, larvae and adults form dense colonies. Trademark beardlike threads up to 4 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 excretions.

The giant whitefly is resistant to chemical treatment. The giant whitefly will simply return — stronger and more pervasive. It is too widespread and breeds far too quickly for agricultural officials to be able to eradicate it at this point.

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. The use of whitefly sticky traps, placed adjacent to host plants, also aid in slowing the pest down.

If you don’t have time to wash your plants every day, both insecticidal soaps and horticultural oils will kill adult whiteflies and immature larvae through suffocation. Because these chemicals have little residual activity, they are not as harmful to beneficial insects; however, they must be applied weekly. Thorough coverage of the undersides of leaves is essential.

Catharine and I heard Buster’s insistent barking between catching house flies in mid-air. He certainly has developed a knack of doing so. I petted our dog and mused for a moment: I hope he learns to catch giant whitefly. See you next time.

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