January 22, 2009 at 8:03 a.m.
Insects that love houseplants
Insects that love houseplants
Spider mites are among the most serious houseplant pests. Left unattended they can multiply rapidly, causing defoliation and death of the plant. They are not true insects but are more closely related to spiders and ticks. They are oval shaped and yellowish or greenish in color. They are so small that they are difficult to see with the naked eye. The mites thrive in dry, warm conditions. They make their way indoors in the fall from other plants brought into the home and even from Christmas trees and greenery during the holiday season. Spider mites feed on the underside of leaves, then move from stem to stem and onto nearby plants by means of fine webbing. People can also accidentally spread them with their hands, clothing, tools, and watering cans.
They damage plants by piercing leaf tissue with needle-like mouthparts that feed on the sap. Usually the first sign of spider mites are a mottled or pinprick yellow discoloration of the underside of leaves. Control includes washing and using insecticidal soap. It usually takes two applications spaced seven to ten days apart.
Scale insects don't look like the typical insects. Adults secret a waxy shell-like covering that give them the appearance of brown or grey bumps. They are round, oval or oyster shell shaped, roughly one-sixteenth to one-eighth inch in diameter. The young have legs and are more mobile and more vulnerable to pesticides than the stationary adults, but are barely visible without magnification.
Scales are usually found on plant stems and the undersides of leaves, especially along mid-veins. They use needle-like mouthparts to feed on plant sap, secreting sticky honeydew as an end product. Heavy feeding causes leaves to yellow and drop, slowing the growth of and stunting the plant.
Control options include washing, insecticidal soap, resmethrin, and disulfoton. Treatments need to be repeated two to three times with 10 to 14 day intervals between treatments. Adding a few drops of liquid dish soap to the insecticide will help it to slide under the protective shell of these insects.
Mealybugs are soft-bodied insects about three-sixteenth inch long, easily visible without magnification. Their bodies have white, waxy filaments protruding from the tail end and look like they have been dusted with flour. They can be confused with powdery mildew. Sometimes they are observed as tiny cotton clusters on stems and leaves.
They are commonly found along veins on the underside of leaves and where the leaves join the stems. Some mealybugs may also be found below the soil surface on the main stem. They pierce plant tissue with sharp mouthparts and suck out the sap, which results in yellowing leaf drop and poor growth. They can be controlled by washing, physical removal, disulfoton, resmethrin, tetramethrin, and pyrethrins. Several applications may be necessary for control. Be sure to read and follow the label instructions whenever you use a chemical for insect control.
Thrips are slender, barely visible insects that range from tan to black and may have lighter markings. Adults can fly, leap and run rapidly. Young thrips can be whitish, yellow, or orange and carry droplets of black dropping on their backs. They damage leaves and flowers by scraping tissue with their mouths and then feed on the released juices. Damaged foliage will show irregular silver blotches that are speckled with little black dots of excrement. Flowers typically become streaked or distorted. They can be controlled by washing or using insecticides.
When a houseplant is heavily infested and badly damaged, the best course of action is to throw the plant away so other plants are not exposed to the same pest problem. If you are reluctant to dispose of the plant, prune it practically to the soil and watch new growth carefully for signs of infection.
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