Several different species of whiteflies damage plants, and gardeners need to know which is the best whitefly pesticide. Generally, botanists advise against strong chemical pesticides or insecticides and recommend different methods of biological control such as using whitefly predators, hosing down the infected plants, or using an agricultural soap or insecticide oil. Most whitefly infestations are a result of an imbalance in the natural environment, and control is very challenging.
Although there are several species of whiteflies, the most common is the greenhouse whitefly, or Trialeurodes vaporariorum. In all of the species, the tiny larva, not the adult fly, damages plants. First, the larva sucks the juices from the plant, and a large infestation of larvae can kill a plant. Another way that the larva injures a plant is through the honeydew that it secretes while feeding. This sticky, sweet substance attracts other harmful insects and often grows a harmful fungus that infects the plant.
Botanists prefer not to use a whitefly pesticide, but to use one of the non-chemical methods. One of these methods is to introduce whitefly predators, such as lacewings, parasitic wasps, and ladybugs. Even the Asian multicolored lady beetle, or Harmonia axyridis, attacks whiteflies. Some of the effective wasp parasites are the Encarsia formosa, Encarsia luteola, and Eretmocerus californicus, although not one species is effective against all species of whiteflies. Consult an agriculturalist or botanist to identify the species of the invading whitefly and to recommend the right species of parasitic wasp.
Another way to control the insects without using a whitefly pesticide is by vacuuming the plants. Generally, a gardener uses a small, handheld vacuum cleaner that is battery operated. If a person vacuums the plants in the early morning when the temperatures are lower, he or she usually has better results. The flies are less active at that time of the day. After vacuuming as many insects as possible, place the vacuum contents into a sealed plastic bag and freeze it overnight; throw away the dead insects without opening the plastic bag.
Some gardeners do not use a whitefly pesticide, but rather they have success by hosing the infected plants with plain water. Often botanists refer to this technique as syringing and warn that it is only effective if the plants are thoroughly sprayed. Another technique is to use sticky traps. Gardeners can buy these traps commercially or find instructions for homemade traps on the Internet.
Some of the control techniques have multiple advantages. One of these is reflective mulch. Mulching with aluminum foil or commercial reflective mulch often is effective at controlling whiteflies. The advantages of mulching include weed control and lessened water evaporation. It is important to cover or remove the reflective material during the hot season, or the plants may burn.
Even though botanists prefer biological control methods, one whitefly pesticide is neem oil. This derivative of the Asian evergreen neem tree, called neem oil, is available at most garden centers and online from gardening, horticultural, and agricultural suppliers. Neem oil has insecticidal properties and is effective as a contact poison. This spray has limited success because it kills only on contact. Another drawback to using this as a whitefly pesticide is that it kills beneficial insects too.
Another chemical control is agricultural or insecticidal soap. Like the neem oil, it has inadequate success at ridding the plant of a whitefly invasion. Insecticidal soap is a potassium fatty acid soap that may damage the plant if used improperly. Gardeners generally use insecticidal soap because it attacks only soft-bodied insects, such as the whitefly.