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Get rid of those pesky whiteflies

Jessica Walliser
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The leaves of this lantana plant are infested with whitefly nymphs and adults.

Whiteflies are tiny, moth-like flies measuring just 1/10-inch long. Though they’re small, whiteflies can cause big problems for houseplant growers. They’re most noticeable when populations are high and a cloud of tiny white flies lifts off of the plant after it’s been disturbed. Just a few adults or eggs on a plant can quickly explode into hundreds of individuals in a warm house.

Almost any plant is susceptible to whitefly damage, but preferred houseplant hosts include citrus, geraniums, plumeria, begonias, jasmine, hibiscus and poinsettias.

Active year-round in Southern climates, whiteflies overwinter here in Pennsylvania in greenhouses and homes. Occasionally, if we have a mild winter, they can even overwinter outdoors, typically as nymphs. For homeowners, whitefly infestations often start when an infested plant is brought home from a nursery. Whiteflies are sneaky and sometimes nursery owners aren’t even aware they have an issue because the whiteflies are still in the egg or nymph stage. Whiteflies can also become an issue when houseplants spend the summer outdoors on a patio or porch; the insects find them, and then the plants are brought back indoors.

Outdoor populations of whitefly seldom do significant damage this far north, though they can become problematic on vegetables like tomatoes, eggplants and peppers, along with certain bedding plants, including geraniums. There are many natural enemies of whiteflies, including lacewing larvae, ladybug larvae, spiders, minute pirate bugs and several other species of predatory bugs and beetles. In outdoor environments, these natural enemies naturally help manage whitefly populations.

Whitefly nymphs and adults feed by sucking plant juices, causing weakened growth, leaf yellowing and possible leaf drop. They’re often found clustered on leaf undersides in large groups. The nymphs are wingless and smaller than the adults. Eggs are extremely small and difficult to find.

On houseplants where whiteflies are present, remove infested leaves immediately to reduce numbers. Place yellow sticky cards on stakes around affected plants. Whiteflies are attracted to the yellow color and get trapped on the glue.

Sprays of insecticidal soap, horticultural oil and citrus oil are effective, but applications must cover the insects themselves, a task that can be somewhat difficult as the adults quickly take flight. Repeat applications are often necessary. Isolate infected plants and watch other houseplants carefully for early signs of infestation. This pest is best controlled before its population gets out of hand.

Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio with Doug Oster. She is the author of several gardening books, including “Attracting Beneficial Bugs to Your Garden,” “Good Bug, Bad Bug,” and her newest title, “Container Gardening Complete.” Her website is jessicawalliser.com. Send your gardening or landscaping questions to [email protected] or The Good Earth, 622 Cabin Hill Drive, Greensburg, PA 15601.

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