Whiteflies and Gnats

Adult whiteflies resemble tiny white moths. They are about 1/16th of an inch long, and white with four wings, and may be covered with a powdery white wax. The nymphs or immature whiteflies resemble flat disks on the undersides of the leaves and may or may not be covered with wax. Whiteflies injure plants by sucking plant sap. They excrete honeydew, which gives the plants a sticky appearance and supports the growth of black sooty mold. Heavy whitefly infestations can cause stunted, distorted, and discolored leaves, and the plant may not grow well. To control whiteflies on houseplants, spray the undersides of leaves with an insecticidal soap labeled for use on houseplants or with a houseplant insecticide spray. You will need to repeat the spray as new whiteflies hatch out. Be sure the both plant and pest are listed on the label, and follow label directions very carefully. And please note that using liquid dish soap may not control the pest and could cause plant injury- insecticidal soaps have been tested and formulated to work properly.

Fungus gnats are harmless to humans and animals but can become a nuisance indoors when adults emerge in large numbers as mosquito-like insects from potted plants or flower boxes containing damp soil that is rich in humus. Adults are attracted to lights and are often first noticed at windows. Larvae or maggots can injure the roots of bedding plants, African violets, carnations, cyclamens, geraniums, poinsettias and foliage plants. Plant symptoms may appear as sudden wilting, loss of vigor, poor growth, yellowing and foliage loss.

To prevent fungus gnats:

• Inspect plants carefully before purchase and before bringing them back indoors for the winter for signs of insect infestation. Discard if heavily infested with any insect and unable to save.


• Always use sterile potting soil.


• Overwatering, water leaks and poor drainage may result in buildup of fungus gnats. Allowing the soil to dry as much as possible, without injury to the plants, is effective in killing many maggots.


• Remove all old plant material and debris in and around the home. Practice good sanitation.

To see the fact sheet from Ohio State University on fungus gnats go to: http://ohioline.osu.edu/hyg-fact/2000/2114.html or call your county extension office. In Lackawanna County ask for the Garden Help line at 963-6842 or email LackawannaMG@psu.edu


Terry Schettini, Extension Educator
Penn State Cooperative Extension in Lackawanna County