Photo courtesy of Bayer

Breeding year-round and colonizing on leaf undersides, whiteflies may be difficult to control, but proven control methods exist, explains Dr. Aaron Palmateer, Green Solutions Team specialist and senior technical service representative with Bayer.

Greenhouse Management: What are the symptoms and signs of a whitefly infestation?

Dr. Aaron Palmateer: When actively feeding, whiteflies can cause leaves to turn yellow and then brown as the leaf tissue dies. Large colonies typically develop on the undersides of leaves, laying tiny oblong eggs ranging from yellow to white in color. After they hatch, the young whiteflies go through four nymphal stages, with winged adults emerging from the last stage.

GM: How do whiteflies affect your crop?

AP: All stages of whiteflies feed by sucking plant juices from leaves and excreting excess liquid as drops of honeydew. In addition to the destructive feeding damage, the honeydew excretions provide a source of nutrition for sooty mold fungi, which readily colonize plant tissues as they feed on the honeydew and cause any affected surfaces to blacken and ultimately reduce overall plant quality.

GM: Why are whiteflies so difficult to control?

AP: In warmer climates, whiteflies can breed year-round and quickly build up to high numbers on susceptible plants. Colonies occur on the underside of leaves, making them difficult to target. Over the years, whiteflies have also developed resistant populations that can withstand triple the amount of insect control products that was successful a decade ago. This makes it important to rotate insecticides with different modes of action. It’s good stewardship not to apply more than two sequential applications of any insecticide within the same Insecticide Resistance Action Committee (IRAC) group.

GM: What cultural practices can growers implement to protect their plants from whiteflies?

AP: Identify and closely monitor plants known to host high whitefly populations, then isolate affected plants and break off leaves supporting high infestations. Ornamental plants that are highly attractive to whiteflies include poinsettia, hibiscus, ivy, gerbera daisy, lantana, verbena, garden chrysanthemum, salvia and mandevilla. Weeds can also be favorable hosts for whiteflies and should be removed or controlled with herbicides. Yellow sticky traps can aid in monitoring and may help to reduce high populations.

GM: Are there any new developments in whitefly control?

AP: Altus® insecticide was recently introduced to the ornamental market to control sucking pests. It is an entirely new class of chemistry, butenolide, placed in IRAC group 4D. It is upwardly systemic and has translaminar capabilities, allowing it to move readily through leaf tissue. Thus, foliar applications over the plant canopy will target insect pests found on the underside of leaves. Altus is labeled for use before, during and after bloom.