White Flies

The greenhouse whitefly (Trialeurodes vaporariorum) and the silverleaf whitefly (Bemisia argentifolii) commonly occur in greenhouses and interiorscapes. Greenhouse whitefly adults hold their wings nearly parallel to the leaf surface and appear broader-winged; adult silverleaf whiteflies hold their wings at a 45-degree angle similar to the roof of an A-frame house. Pupae of the greenhouse whitefly appear coin-like in shape (with sides perpendicular to the leaf surface). Silverleaf whitefly pupae typically appear more rounded with edges that slant slightly toward the leaf surface.

Adults are less than 1/8” long and, like their name suggests, have white wings with pale yellow bodies. Adult whiteflies congregate above and under leaf surfaces, and disperse in clouds when disturbed.

Life Cycle

Greenhouse whiteflies develop in 30-34 days; silverleaf whiteflies develop in 35-39 days. Both species develop according to the following life cycle stages:
-Egg (hatch in about 8-11 days)
-Crawler (lasts about 7 days)
-Nymph (three instars - about 10 days)
-Pupa (doesn’t feed)
-Adult

Damage

Whiteflies feed on plant juices using piercing-sucking mouthparts causing stunted growth, leaf yellowing and reduced yields. Whiteflies are able to reproduce quickly, spread rapidly and are considered a major economic pest of greenhouse crops. Whiteflies have a wide host range and thrive on hundreds of ornamental and crop plants such as pointsettia, cabbage, tomato, mustard, cucumber, bush beans, peppers and soybeans (just to name a few).

Control Strategies

Monitor on a regular basis. Inspect new plants by checking for adults, pupae, nymphs and eggs. Use yellow sticky cards to detect infestations in their early stages. Develop a weekly monitoring schedule and note where infested plants are located.

Prevent whiteflies from entering growing areas with screens over intake vents and by keeping doorways closed. Keep unused growing areas empty when possible between crops. Remove plants around the perimeter of the greenhouse that may harbor pests. Dispose of infested plants and plant debris in sealed plastic bags to prevent reinfestation. Avoid overfertilization.

Pesticides can be used to control whiteflies but be sure to keep in mind:

1) Foliar pesticides are effective when there are mostly crawlers, nymphs, or adults present (soil systemics may provide better control) 2) Plant surfaces, including the undersides of leaves, need to be covered for foliar applications to be effective 3) Prevent insecticide resistance by avoiding consecutive treatments using the same chemical class. Yellow sticky traps, cinnamon oil, insecticidal soap and capsaicin are all suggested remedies for white fly infestations.

Both greenhouse and silverleaf whiteflies have natural enemies that are available for commercial use, such as the black ladybeetle. The use of biological control agents has been effective for suppressing whitefly populations in indoor plantscapes and in greenhouses as a part of an IPM program. As a general rule, making several small releases over a period of time rather than one single massive release is recommended for best results. If pesticides are used, waiting a minimum of two weeks and/or two waterings before releasing biological control agents is advised.