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Leave the Bugs Out in the Cold When You Bring Your Houseplants Into the Warmth

More Bugs: Soft-shell scale, mealy bugs, spittle bugs, spider mites and cyclamen mites

A number of insects feed unnoticed on houseplants until perplexing changes alert you. Yellowing leaves are often seen as an indication that the plant is hungry and needs a dose of fertilizer. Yellowing leaves can also mean soft-shell scale insects are feeding on your rubber tree, crotons, philodendrons or related foliage plants. In sufficient numbers, these insects can cause leaves to turn yellow and appear deficient in nutrients.
    Look for scale insects on stems, veins in leaves and leaf tissues between the veins.
    Treat scale insects on houseplants by spraying the foliage thoroughly with horticultural oil at a two percent concentration. If the plant is small, dunk its foliage in the horticultural oil solution. By dunking and shaking the foliage in the solution, you thoroughly cover all infested tissue. If the plants cannot be dunked, then you must spray thoroughly. This may require moving the plant outdoors on a warm day.
    Crotons are extremely susceptible to another plant pest, mealy bugs. These bugs appear as a small, grey-white, mealy-looking glob the size of a pea. The waxy coating protects the insect hidden inside. When plants are heavily infested with mealy bugs, the best treatment is moving them outdoors and spraying thoroughly with a strong blast of water from the garden hose. After the plant is brought back indoors, monitor weekly and remove newly formed mealy bugs as they appear.
    Spittle bugs favor begonias and hibiscus. These small insects appear as blobs of spit, most often in the axils of leaves and stems. Spittle bugs are the least harmful of all plant insects, but their presence detracts from the appearance of the plant. Spraying with plant-shine is often sufficient to control a light infestation. A strong spray of water works for heavy infestations.
    Smaller than a grain of salt, spider mites often go unnoticed until you see tiny webs connecting leaves, stems and flower buds. Spider mites favor miniature roses, marigolds, African violets, orange trees and some of the plants used in making bonsai.
    If you suspect spider mites, place a white sheet of paper under the plant and tap it several times with your hand. If spider mites are present, you will see small specks moving about on the paper.
    Control spider mites on houseplants by spraying or dunking the plants with horticultural oil at a two percent concentration. The oil will kill both adult mites and eggs. However some of the eggs drop to the soil, so these persistent pests will reappear and multiply rapidly.
    If you are growing cyclamen, there is a good possibility that your plants are infested with unnoticed cyclamen mites. Cyclamen grow from a tuber that provides ample opportunities for the mites to hide.
    Greenhouse growers treat their tubers in 120-degree water before planting. This requires a very accurate thermometer because water temperatures above 122 degrees will kill the tuber. The tubers are placed in the hot water and swirled around for exactly one minute before being dunked in a two percent horticultural oil solution.

Ask Dr. Gouin your questions at [email protected]. All questions will appear in Bay Weekly. Please include your name and address.