• Topics: Entomology and Nematology  | Landscape Pests  | Ornamentals (MG Entomology)  | Landscape Whitefly Pests  | Buss, Eileen A 

Whiteflies on Landscape Ornamentals¹

Whiteflies are common pests on many ornamental plants. Some plants most frequently attacked include allamanda, chinaberry, citrus, fringe tree, gardenia, ligustrum, viburnum, persimmon, and many annuals.

Adult whiteflies (Figure 1) look like tiny white moths, but are more closely related to scale insects. They are only about 1/16 inch long and have four wings. The wings and body are covered with a fine white powdery wax. The immature stages (nymphs) which are found on the underside of leaves are flat, oval in outline, and slightly smaller than a pin head. They are light green to whitish and somewhat transparent (Figure 2).

Figure 1. 

Spiraling whitefly adult.

Figure 2. 

Giant whitefly adult and nymphs.

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 about for several hours, then insert their mouthparts into the leaves and remain in one place for the rest of their immature stages. After molting three times they pupate (resting stage) and are transformed into the adult. The length of the life cycle from egg to adult varies considerably, requiring from 6 weeks to 6 months (winter generation). There are three generations of whiteflies in Florida. In the Gainesville area, these occur in late March, mid June, and late August. They will be approximately 2 to 3 weeks earlier in south Florida and about 1 week later in north Florida.

Whiteflies have piercing-sucking mouthparts with which they puncture the leaf and suck the plant juices. Top sides of leaves on infested plants become pale or spotted due to these insects feeding on the undersides of the leaves. Whiteflies as well as soft scales, mealybugs, and aphids excrete large amounts of honeydew which provides an excellent medium for the growth of a black fungus called sooty mold. Besides being unattractive, sooty mold may interfere with photosynthesis, retard the growth of the plant, and cause early leaf drop. Sooty mold usually weathers away following control of the insect infestation. Ants feed on the honeydew and when ants are noticed, plants should be examined closely for these sucking pests.

Citrus whitefly nymphs, (Figure 3) one of the more common whitefly species attacking ornamental plants other than citrus, are highly parasitized by a small wasp, Prospaltella lahorensis. These parasites were first released in Gainesville and Winter Haven in 1972. Citrus is the primary host of the cloudy winged whitefly, a species closely related to the citrus whitefly. The citrus blackfly is also under biological control due to two tiny wasps which have spread throughout the state after being introduced in Fort Lauderdale.

Figure 3. 

Citrus whitefly nymphs.

Carefully examine infested plants for evidence of parasitism. Parasitized whitefly nymphs will contain the larva or pupa of the parasite or an emergence hole may be visible on a nymph. The parasite does not attack the adult whitefly. If parasitism is evident, avoid using insecticides. Chemical control would prevent the increase of the parasite which could control the pest.

During recent years, the silverleaf (sweetpotato) whitefly has replaced the citrus whitefly as the major whitefly species attacking ornamental plants, especially in South Florida. This whitefly is not yet parasitized to any extent and is difficult to control with chemicals. This species is not attacked by Prospaltella lahorensis.

Some whiteflies may also be naturally attacked by fungi (Paecilomyces) (Figure 4).

Figure 4. 

Infected whiteflies.

Chemical Control

Insecticides that are labeled for whitefly control in residential areas are listed in Tables 1 and 2.

If the whitefly species is hard to control with these products, then it may be the silverleaf species, or QBiotype. Soap or oil sprays are the most effective for homeowners to use against this particular whitefly and are safe to people and the environment. Follow label directions. Thorough coverage on the undersides of the leaves to the point of run-off is especially important when using soap or oil sprays. If a commercial soap or oil is not available, a homemade mixture can be made by mixing 2 tablespoons of dishwashing liquid (do not use those containing a degreaser or an automatic dishwashing soap or detergent) and 2 tablespoons vegetable cooking oil per gallon of water. Repeat at weekly intervals as needed.

For More Information

• Entomology and IPM for Foliage Plants (http://www.mrec.ifas.ufl.edu/LSO/bemisia/bemisia.htm)

• FDACS Pest Alert (http://www.doacs. state.fl.us/pi/enpp/ento/b.tabaci.html)

• Insecticide Resistance Action Committee Website (IRAC) (http://www.irac-online.org)

• Whitefly Knowledgebase (http://whiteflies. ifas.ufl.edu)

Tables

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer-Chancy, Interim Dean.

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