Whiteflies are one of the most easily identified of all greenhouse insect pests. True to their name, whiteflies are tiny (about .06 inches long) whitish insects with four white wings. There are several species of whiteflies, collectively infesting more than 250 ornamental plants. Favorite hosts include lantana, poinsettia, nicotiana, tomato, bean, hibiscus, eggplant and geranium.
Whiteflies cause damage by sucking sap from the leaves of plants. Heavily infested plants will weaken and leaves will turn yellow and drop. Whiteflies, like other insects that feed on sap, excrete a sugary substance called honeydew, which is quite sticky. Black sooty mold grows on the honeydew and further discolors the leaves.
Eggs, nymphs and adults can be easily seen on the undersides of the leaves. Adults will fly up quickly if the leaves are brushed. Because of this, even a low-level infestation, while not immediately harmful to the plant, will turn off customers.
It’s important to continuously monitor for the presence of whitefly using yellow sticky cards and visual inspection. Control methods include biological methods such as parasitic wasps, predatory lady bird beetles, traditional chemical controls such as imidacloprid, horticultural oils and Beuvaria bassiana, a biofungicide.
Whiteflies have several life stages. The first instar nymphs emerge from the eggs, crawl a short distance and feed. There are three more nymphal stages, which do not move. Eggs and pupae are often unaffected by insecticides. Only the adults fly, and this is how the population spreads.
It is important to correctly identify the species of whitefly, because control methods and timing may be different. There are several species common to greenhouses: the greenhouse whitefly, (Trialeurodes vaporarium), sweetpotato whitefly (Bemisia tabaci) and the silverleaf whitefly (Bemisia tabaci, Biotype B). Many whitefly populations are resistant to chemical controls, so insecticide applications should be used judiciously and combined with non-chemical control tactics. Eggs and pupae are often unaffected by insecticides.
Prevention is the best method of control. Careful sanitation practices should be followed and any plants, including weeds, that may serve as a host for whitefly in between crops should be removed. New plants coming into the greenhouse should be carefully inspected for eggs and immature stages.
Cranshaw, W.S. 2007. Greenhouse Whitefly. Colorado State University Extension. http://www.ext.colostate.edu/pubs/insect/05587.html
Natwick, E. T., J. J. Stapleton and C. S. Stoddard. 2012. University of California IPM Online. Whiteflies. http://www.ipm.ucdavis.edu/PMG/r116301211.html
Pundt, Leanne. Managing Whiteflies in the Greenhouse. University of Connecticut Integrated Pest Management. http://www.hort.uconn.edu/ipm/homegrnd/htms/48ghwfl.htm