Thursday, February 6, 2014

Winter Whiteflies Feast on Indoor Plants

If you've moved container plants such as herbs and other edibles indoors for the winter, you may have noticed a dusting of white insects on the leaves. This critter can often identified as the Greenhouse Whitefly.
Here is some helpful information from the North Carolina Extension Office on Whiteflies. (Your best treatment options are horticultural soaps and oils to not poison household pets or outdoor critters, like honeybees, when you move the plant back!)

Whiteflies make a home on a potted mint,
Mentha piperitaPhoto by J. Corser.

By: Steven Frank and James R. Baker, Extension Entomologist Emeritus

CAUTION: This information was developed for North Carolina and may not apply to other areas.

General Information
GREENHOUSE WHITEFLY, Trialeurodes vaporariorum (Westwood), Aleurodidae, HOMOPTERA

The greenhouse whitefly is a tiny (1/16 inch long insect that resembles a tiny moth). The almost microscopic, oblong, pale green to purple eggs are inserted into the lower leaf surface, often in a circle or crescent. The tiny nymph, yellow with red eyes, becomes a flat scale-like insect appressed to the lower leaf surface that grows to about 1/32 inch long.
Greenhouse whiteflies are worldwide pests of greenhouse-grown ornamentals and vegetables. First discovered in England in 1856, they were found in the United States in 1870. Tropical Central or South America are suggested origins of the greenhouse whitefly. Greenhouse whiteflies infest a wide variety of ornamental and vegetable crops, and they can survive outdoors during the growing season, particularly in sheltered locations. Even trees may be infested (redbud, Kentucky coffee berry, and avocado). Infested plants become chlorotic and unthrifty. Secondary infections of honeydew and sooty mold further detract from the appearance of the crop. Unless controlled, greenhouse whiteflies may completely destroy the commercial value of a floricultural crop. Greenhouse whiteflies reproduce slowly (a generation every 30 to 45 days), but each female may lay up to 400 eggs and live as long as 2 months. Adults are usually found on the lower surface of new
leaves. Here they insert their eggs that hatch 5 to 7 days later. The new crawlers move about the plant for a day or two, often from leaf to leaf before inserting their mouthparts to feed. Once this occurs, they probably do not move again until mature. The crawlers molt into nymphs and then pupae. Finally, a new generation of whitish-yellow adults emerges. They are soon covered by a white, waxy bloom.

It was previously thought that lower greenhouse temperatures used in the culture of some bedding and potted plant varieties tended to encourage infestations because naturally occurring parasitic wasps (Encarsia formosa) are reproductively inhibited at temperatures below 75F. This does not seem to be the case. The Encarsia formosa, now in the commercial biological control trade, seems to works well at most greenhouse temperatures. Chemical control of whiteflies is difficult because the eggs and immature forms are resistant to many aerosol and insecticide sprays. One must make regular applications of pesticides to control emerging adults until the last of a whole  generation of immature whiteflies has emerged.

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