What are the symptoms and signs of a whitefly infestation?
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.
How do whiteflies affect your crop?
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. Sooty mold fungi readily colonize plant tissues as they feed on the honeydew, causing any affected surfaces to blacken from an abundance of spores and ultimately reducing overall plant quality.
Why are whiteflies so difficult to control?
In warmer climates, whiteflies can breed year around, moving from one host to another as plants go through the production cycle. Whiteflies can quickly build up to high numbers on susceptible plants, such as poinsettias. Colonies occur on the underside of leaves, making them more difficult to target – especially when using contact insecticides. 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 very 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.
What cultural practices can growers implement to protect their plants from whiteflies and other sucking pests?
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.
Are there any new developments in whitefly control?
Article originally published in Greenhouse Management, November 2017