WHITEFLY CONTROLWhiteflies are tiny, sap-sucking insects that are frequently abundant in vegetable and ornamental plantings. They excrete sticky honeydew and cause yellowing or death of leaves. Outbreaks often occur when the natural biological control is disrupted. Management is difficult. When speaking of whiteflies, at least for the purpose of biological pest control, the general identification of this pest is usually not enough -- especially if you are working with a budget. Proper identification down to genus is fundamental if you want to control whitefly infestations at the lowest possible cost.
There are three whitefly species of particular concern to growers (although there are more than three species of whitefly which can be considered problematic): the greenhouse whitefly, the silverleaf whitefly, and the sweet potato whitefly. You can determine the differences identified in the pupae of the whitefly. The pupae of the greenhouse whitefly are raised with sides perpendicular to the leaf's surface and fringed with hair-like growths. The silverleaf and sweet potato whitefly pupae are dome shaped and lack most of the hairs.Another way to tell them apart is to look carefully at the adults themselves although this is the least reliable method. The wings of the greenhouse whitefly appear wider and lay more flat. The other species have thinner wings that are tented and more at a right angle.
HOST PLANTS: Whiteflies are mostly found in vegetable or ornamental plantings.
SYMPTOMS: Whiteflies suck phloem sap. Large populations can cause leaves to turn yellow, appear dry, or fall off plants. Like aphids, whiteflies excrete honeydew, so leaves may be sticky or covered with black sooty mold. The honeydew attracts ants, which interfere with the activities of natural enemies that may control whiteflies and other pests.
Feeding by the immature silverleaf whitefly can cause plant distortion, discoloration, or silvering of leaves and may cause serious losses in some vegetable crops. Some whiteflies transmit viruses to certain vegetable crops. With the notable exception of the citrus whitefly, whiteflies are not normally a problem in fruit trees. Low levels of whiteflies are not usually damaging. Adults by themselves will not cause significant damage unless they are transmitting a plant pathogen. Generally, plant losses do not occur unless there is a significant population of whitefly nymphs..
WHITEFLY CONTROL: Hand-removal of leaves heavily infested with the nonmobile nymphal and pupal stages may reduce populations to levels that natural enemies can contain. Water sprays (syringing) may also be useful in dislodging adults.A small, hand-held, battery-operated vacuum cleaner has also been recommended for vacuuming adults off leaves. Vacuum in the early morning or other times when it is cool and whiteflies are sluggish. Kill vacuumed insects by placing the vacuum bag in a plastic bag and freezing it overnight. Contents may be disposed of the next day.
In vegetable gardens, yellow sticky traps can be posted around the garden to trap adults. Such traps won’t eliminate damaging populations but may reduce them somewhat as a component of an integrated management program relying on multiple tactics. Whiteflies do not fly very far, so many traps may be needed. You may need as many as one trap for every two large plants, with the sticky yellow part of the trap level with the whitefly infestation. Place traps so the sticky side faces plants but is out of direct sunlight.
Whiteflies have many natural enemies, and outbreaks frequently occur when these natural enemies have been disturbed or destroyed by pesticides, dust buildup, or other factors. Reintroduce predators such as green lacewings, delphastus catalinae, or parasitic wasps such as encarsia formosa or eretmocerus eremicus. Avoiding the use of insecticides that kill natural enemies is a very important aspect of whitefly management. Products containing carbaryl, pyrethroids, diazinon or foliar sprays of imidacloprid can be particularly disruptive. Control of dust and ants, which protect whiteflies from their natural enemies, can also be important, especially in citrus or other trees.