Whiteflies are a familiar houseplant pest, but don’t think you’ve escaped them just because it’s spring and you’re now busy in the garden. There are more than 1200 species of whitefly, and they can wreak as much havoc outdoors as indoors. They’re hard to detect because they tend to congregate on the undersides of leaves, so typically the first sign of an infestation is a cloud of tiny white insects that rises when you brush against a plant. Whiteflies are about 1/10- to 1/16-inch long, and they look like tiny white moths. They’re not really flies, but are related to other sap-sucking insects like scale insects and aphids.
Whitefly larvae feed on a plant’s sap. A heavy infestation weakens the plant. Leaves turn yellow and drop, or they may become coated with a black powder. This black sooty mold grows on honeydew, a sticky liquid that the whiteflies excrete onto the leaf surface. Plants infested with whiteflies can be stunted or defoliated, produce a smaller harvest, or even die. In some cases, whiteflies can carry viruses from plant to plant.
Prevention is important. Inspect all plants you bring into your yard. If you find whiteflies, quarantine the infested plant until you’ve removed the pests. You can pinch off leaves where whitefly larvae are feeding.
Natural predators like spiders, lady beetles, and lacewings will keep whiteflies under control in your garden, as long as you provide an insecticide-free yard for the predators to thrive in.
You can use “yellow traps” (make your own or buy them), which are basically cardboard strips painted yellow and covered with mineral oil, petroleum jelly, or something similar. The whiteflies are attracted to the yellow and get stuck. Unfortunately, these traps can also attract whiteflies’ natural predators.
Another strategy is to vacuum the whiteflies. This works best when the infestation is light and there aren’t many eggs yet. Do it in the morning, when the insects are moving slow. Put the vacuum bag in a plastic bag and put that in the freezer for 24 hours.
Chemicals can be used to fight whitefly infestations, but some whitefly populations have developed resistance to certain products. Check with your extension service to find out what works in your area.
— photo courtesy of the Kemper Center for Home Gardening at the Missouri Botanical Garden.