December 10, 2015 – Kenosha News
Question: I brought my plants indoors in early October before we had frost. A couple of plants don’t look good. I think they may have bugs. What should I do? A.R.
Answer: Start by taking a close look at the plants. Check the underside of leaves and the leaf axils, where the leaf comes out of the stem. It might help to use a magnifying glass because insects and mites are tiny, less than 1/8 to 1/16 inch long. Look for webbing, shiny sticky leaves and abnormal bumps and spots.
Spider mites spin fine webbing across leaves and between the leaf and stem. Mites look like tiny specks moving through the webbing or on the underside of leaves. Mites feed by piercing plant cells and sucking out the cell’s contents. Lightly infested leaves have pale blotches or spots. With heavy infestations entire leaves become light green or bronzy in color, often with a brownish border, and eventually die.
Sticky or shiny spots on the leaves are probably caused by one of three kinds of sap sucking insects. They excrete a sticky substance called honeydew, which makes plant leaves shiny and sticky to the touch. Aphids are pear-shaped insects that vary in color from pale green to yellow to pink. Aphids feed in colonies on buds, young stems, and along the veins of the leaves. Scale insects look like hard, round or oval, brown or gray bumps on leaves or stems. Scales may be difficult to see because they resemble part of the plant. Scales can be rubbed off with a finger. Mealybugs are 1/8 inch long oval pink insects. Older mealybugs are covered with white waxy strands that make them look like tiny cotton balls.
Houseplant pests are difficult to control and need to be treated regularly for several weeks or even months. A weekly water only shower in the sink or tub will flush many of these pests down the drain but usually isn’t enough to eliminate the problem. Insecticidal soap is recommended and fairly effective especially when the foliage thoroughly covered. Read and follow label directions on the insecticidal soap for the frequency of application for the type of pest. Insecticidal soap should not be used on some plants so check and follow label directions.
Horticultural oil is another option for spider mites, scales, and mealybugs on houseplants.
Quarantine infested plants by moving them to another room away from your healthy plants. Otherwise, the insects may travel from an infested plant to a healthy one.
Barb Larson is horticulture educator for the Kenosha County University of Wisconsin Extension. She holds a master’s of science in horticulture from the University of Wisconsin-Madison. If you have a plant or gardening question, email her at email@example.com or call 262-857-1942.