Whitefly Information and Control
Whiteflies are common pests on many ornamental plants. Some of the most economically important species in Florida are the silverleaf whitefly, fig or ficus whitefly, citrus whitefly, and the rugose spiraling whitefly. The most frequently attacked plants include allamanda, avocado, chinaberry, citrus, fig, fringe tree, gardenia, gumbo limbo, ligustrum, mango, various palms, persimmon, viburnum, and many annuals.
Adult whiteflies look like tiny white moths, but are more closely related to scale insects. Most are about 1/16 inch long and have four wings. The wings and body are covered with a fine white powdery wax. Reliable identifications are based on the adults. The immature whiteflies (nymphs) typically occur on the undersides of leaves, are flat, oval in outline, and slightly smaller than a pin head. Some species are light green to whitish and somewhat transparent. Others are black in the center and have a white waxy fringe around the edge.
A generalized life cycle of the whitefly is as follows: The eggs are laid on the undersides of the leaves and hatch in 4 to 12 days into active, six legged nymphs (crawlers). The crawlers move around for several hours, then insert their mouthparts into the leaves and stay there. After molting three times, they pupate and then become adults. The pupal case remains on the plant tissue even after the adult has emerged. How long it takes for the insects to develop from eggs to adults varies from 4 weeks (summer) to 6 months (winter).
Whiteflies have piercing-sucking (needle-like) mouthparts with which they puncture the leaf and suck the plant fluids. The top sides of leaves on infested plants become pale or spotted due to these insects feeding on the undersides of the leaves. Oftentimes an infestation goes unnoticed until leaves turn yellow or drop unexpectedly, or until an infested plant is disturbed and small clouds of whiteflies emerge from it. Some whitefly species can cause greater damage by transmitting plant viruses.
Whiteflies (as well as soft scales, mealybugs, and aphids) excrete a sugary substance called honeydew, and an unsightly black fungus called sooty mold grows on the honeydew. Besides being unattractive, sooty mold may interfere with photosynthesis, reduce plant growth, and cause early leaf drop. Sooty mold usually weathers away after an insect infestation is controlled. Ants also feed on the honeydew, so if ants become a problem, plants should be examined closely for these sucking pests.
The first type of product to try is an insecticidal soap or horticultural oil spray. These products are safer for people, animals, and the environment, but they can still kill whitefly natural enemies. Be sure to read and understand the label instructions before doing any applications. If spraying, thorough coverage on the undersides of the leaves to the point of run-off is especially important. Repeat at weekly intervals as needed.
For synthetic insecticides, be very cautious of overusing the chemical class of neonicotinoids because of the possibility of developing pesticide resistance. Foliar applications tend to be with contact insecticides like pyrethroids. Foliar applications may provide quick control, but do not provide longterm control. Contact insecticides will also disrupt natural enemies and should be used selectively. Other application options include basal bark sprays, granular broadcast applications, tree injections, and soil drenches or injections. The active ingredient of a commonly used systemic insecticide is imidacloprid (ie., Merit, Marathon), but many other products are effective at reducing whitefly populations.