Controlling The Whitefly
June 13, 2012 
The whitefly, a name that encompasses two distinct pests, the greenhouse whitefly and the sweetpotato whitefly, has a broad range of targets including cucurbits, tomatoes, eggplant, peppers, lettuce, beans, and crucifer crops. Dr. Jennifer White, assistant professor in the department of entomology at the University of Kentucky, states that although nymphs cause most feeding damage, adults are also a threat as they transmit viruses.
Greenhouse growers at risk of whitefly infestations should be on guard year-round as the greenhouse whitefly is named for its habitat of choice. Outdoor growers should know that these insects do not have a dormant winter stage, so the southern tier of states usually experiences the most pressure. Northern growers are not off the hook, though, explains White, especially in years that are hotter and drier than the norm.
What To Look For
Although small populations cause little direct damage, a heavy population can cause terrible problems, explains White. Emphasizing that although these pests look similar, like miniature moths with yellow bodies and powdery white wings, and infest similar crops, she says it is important to know the difference as their susceptibility and ability to spread disease is species specific.
She describes the greenhouse whitefly nyphs as,“like a cake with waxy filaments projecting in a fringe from the top.” Sweetpotato whitefly nymphs, however, are more rounded and flush with the leaf with fewer waxy filaments, she explains.
On The Defensive
Whiteflies tend to feed on plant sap, which can reduce plant vigor, growth, and cause withering and premature leaf abscission, reducing yields and killing plants entirely, says White. Although that sounds foreboding enough for most growers, she says, “whiteflies also excrete sticky honeydew while feeding, which promotes the growth of sooty mold and reduces the marketability of some crops.”
In addition, the sweetpotato whitefly in particular causes a distinctive silver leaf formation in some host plants. In combination with the greenhouse whitefly, these pests vector more than 100 viruses including mosaics, leaf curl, and yellowing, which can result in major crop loss, she explains.
The good news is that growers have an array of crop protection options, says White. Cultural control includes floating row covers used early in the season, but she warns that growers need to remove them in time for pollination. In addition, growers should ensure that new plantings
of vulnerable crops do not coincide with the harvest of other crops to prevent whitefly populations from simply moving from one crop to another, growing in number.
For greenhouse growers, screens may help keep whiteflies out. Although this may diminish airflow, White says that adjustments can be made to the ventilation system to compensate. In addition, she emphasizes that a crop-free period will reduce the number of whiteflies, especially if weeds are removed.
White adds that there are many chemical controls (organic and conventional) labeled to control whiteflies. Biological options are a viable alternative, as well, she explains. “Parasitoids, predatory beetles, and mites are readily available from
commercial suppliers.”