11/3/2022 - By Dr. Aaron Palmateer

Whiteflies are tiny, sap-sucking insects that can be major pests to ornamental plants. They can be a nuisance in greenhouse production on susceptible plants pretty much all year round.

Whitefly Lifecycle

When actively feeding, whiteflies cause leaves to turn yellow and eventually brown as the leaf tissue dies. Large colonies typically develop on the undersides of leaves, where they normally lay tiny oblong eggs that range from yellow to white in color. After the eggs hatch, the young whiteflies go through four nymphal stages called instars.

Winged adults emerge from the last nymphal stage. All stages feed by sucking plant juices from leaves and excrete excess liquid as drops of honeydew when they feed. Whiteflies are extremely difficult to control when populations are high, so preventative management is crucial.

There are numerous species of whitefly associated with ornamental plants. The most common species include the greenhouse whitefly (Trialeurodes vaporariorum) and the sweet potato whitefly (Bemisia tabaci). Both have a wide range of plant hosts that include many ornamental crops and weeds.

Ornamental production areas with warmer climates, such as Florida and California, provide opportunities for these pests to breed year-round, moving from one host to another as plants go through the production cycle. Needless to say, they're always on the move.

Whitefly Honeydew Excretion Leads to Sooty Mold Fungi

In addition to the destructive feeding damage whiteflies cause on plants, the honeydew excreted on the affected leaves provides a source of nutrition for sooty mold fungi. Sooty mold fungi are not plant pathogens but readily colonize plant tissues as they feed on the honeydew excreted by the whiteflies.

The fungus causes any affected surfaces (plants, concrete, etc.) to blacken from an abundance of spores and subsequently reduces overall plant quality. The best way to eliminate sooty mold is to control the whiteflies that are feeding on the plant.

Whitefly Management Strategies

Effective whitefly management in greenhouse and nursery production requires a preventative approach. Identify and closely monitor plants known to host high populations of whiteflies because infestations will likely start on the most susceptible plants. Many weeds are susceptible hosts for whiteflies and should be removed or controlled with herbicides.

Yellow sticky traps can be used to aid in monitoring whiteflies and, under high populations, even help to reduce their numbers. The use of biological controls (live predators) can be very effective but limits the choice of chemical insecticides and should be practiced with this consideration.

Contact Your Harrell's Rep!

The best resource you have to answer questions on whiteflies, preventative strategies, and recovery is your local Harrell's rep! reach out today, we're here to help.