Question: Before the weather got cold I moved several potted plants from the patio to the indoors for the winter. I’ve not had problems when I’ve brought plants inside in the past but this year several of the plants have bugs. The bugs are very tiny and light colored. Whenever I touch or bump one of the plants, lots of bugs fly up from the plant. Do you have any suggestions on what I can do? K.C.
Answer: Your plants are infested with whiteflies. Whiteflies are 1/16th inch long with four milky white wings. The nymphs are pale green, flat, and do not fly. When disturbed, the adults fly around the plant, forming a cloud of insects. Nymphs are found on the undersides of the leaves but adult flies may rest anywhere on the plant. Plants infested with whiteflies have yellow leaves and poor growth.
Whiteflies and other houseplant pests are difficult to control. Whitefly infested plants must be treated every five to ten days for several weeks or even months.
Insecticidal soap is a safe option, especially indoors. Spray foliage and stems thoroughly to the point of dripping every five days. Insecticidal soap should not be used on some plants so check and follow label directions. Some gardeners have luck with homemade soap. Wash infested plants with a solution of two teaspoons mild detergent to one gallon lukewarm water. Keep the soap solution out of the soil. After thirty minutes rinse the plant thoroughly. Repeat the treatment every five to seven days until pests are gone. Be careful, many soaps and detergents can damage plant tissue. Test the soap solution on a few leaves of each plant you want to treat. If the leaves are unaffected the following day it should be safe to use your homemade soap solution on the entire plant.
Azadirachtin, which is the active ingredient from the neem tree, is another organic insecticide that you might try. Treat your plants every seven days following label directions.
Several other insecticides, including horticultural oils, are labeled for whiteflies on houseplants. Always read and follow label directions for all types of insecticides.
Whiteflies can be very difficult to eliminate. That’s okay. Just keep the population low enough to keep your plants fairly healthy. When you move your plants back outdoors in May, beneficial insects will get rid of the whiteflies.
Barb Larson is horticulture educator for Kenosha County University of Wisconsin Extension. Barb has a Master’s of Science in horticulture from the University of Wisconsin-Madison. If you have a plant or gardening question, email Larson at firstname.lastname@example.org or call her at 262-857-1945.