PHOTO: Lisa Brown/Flickr
November 7, 2015

Help, I have little white flies all over my plants. Water with white soap didn’t work. Any ideas of what else I can try? — Familia Karachunsky

What you’re describing is most certainly whiteflies, a common pest found in greenhouses and outdoor gardens located in warmer climates. These insects aren’t true flies but rather more closely related to aphids.

Adult whiteflies are pretty distinct—they look like small white moths that quickly flutter when disturbed. Many species of whiteflies can bother vegetable, fruit and ornamental plants, including:

  • Greenhouse whiteflies
  • Giant whiteflies
  • Iris whiteflies
  • Sweet Potato whiteflies

Whitefly species are difficult to distinguish visually and share many characteristics and behaviors.


Whitefly Damage

Check the undersides of leaves for signs of whiteflies.
International Institute of Tropical Horticulture/Flickr

The primary damage from whiteflies is caused by immature nymphs, aka crawlers, and adult whiteflies feeding on leaves. Using their needle-like mouthparts, they suck out plant sap from the vegetation, causing leaves to turn yellow, wilt and die. Mild to moderate infestations will stress young plants and heavy infestations will cause massive leaf damage that can easily kill plants.

Adding to the threat, adults can transmit plant viruses through their mouthparts, as well as secrete a rich sugary liquid called honeydew. Honeydew causes black sooty mold buildup on leaves that, in high levels, can block light to vegetation and attracts ant species that feed on the excretion and actively interfere with beneficial whitefly predators.


Whitefly Control

One of the difficulties in managing whiteflies is that populations will build quickly. An entire whitefly lifecycle takes only about three weeks in optimal conditions, meaning an infestation can happen fast. Unfortunately, they’re especially hard to control due to their protective waxy exterior. You may have some success using insecticidal soaps, but often the most effective organic treatment is the use of horticultural oil sprays. Soaps and oils only will destroy the insects that directly come in contact with them, so these organic sprays need to be applied to underside of leaves from the very bottom of the plant to the topmost leaves to ensure full coverage.

It’s also strongly recommended to remove and destroy heavily infested plants to prevent the spread of whiteflies to other target plants in your yard or greenhouse. And when buying live plants at a nursery or greenhouse, remember to thoroughly check the plant and the underside of the leaves closely for any sign of whiteflies before making a purchase.



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