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Ag Matters column: Check houseplants for mites, insects; wash if needed

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Ag Matters column: Check houseplants for mites, insects; wash if needed
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With a Minnesota winter at its best, we are in "houseplant season," which is when we turn to houseplants to satisfy our itching green thumbs.


It is important that we inspect our houseplants for insect or mite pests that may have developed as the warm, dry environment in many homes is conducive to the development of insect populations.

They may have entered the home on houseplants that were kept outdoors last summer or came in with a holiday gift plant or may even have hitched a ride on the Christmas tree or other greens.

It's common to receive calls from houseplant enthusiasts asking about the sticky substance that they are finding on the leaves of some plants, as well as on the surface of the table or floor beneath them.

This sticky substance is called honeydew and indicates the presence of scale insects, spider mites or mealy bugs. These insects and their relatives are usually found on the undersides of the leaves along the veins, on the stems of the plants and in the axils of the leaves.

They cause injury to the plants by using needle-like mouthparts to pierce plant tissue and feed on the plant's sap.

All three of these pests excrete honeydew, which is a sticky, clear substance made up of excess sugars that are not digested by the pest.

In addition to the presence of this sticky substance, the leav0es of the plants often turn yellow and drop, or in the case of spider mites, the leaves may become stippled with light-colored spots. In severe infestations, the leaves of the plant may be covered with fine webbing.

Spider mites are not true insects, but are spider relatives. They are difficult to see with the naked eye. To verify spider mite presence, place a sheet of white paper under discolored or sticky leaves, then tap the leaves and watch for tiny moving creatures on the paper.

Whiteflies, thrips and aphids may also be a problem and houseplants should be checked for their presence. Although a hand held magnifying glass is helpful in finding these insects, most of them are visible to the naked eye.

As soon as any of these pests are detected, isolate the infested plants. Wash off light infestations of these pests on plants with smooth leaves using a soft cloth and a mild soap solution made up of a teaspoon of mild dish soap mixed in a quart of water.

Because so many dish soaps now contain degreasing chemicals, it may be safer to use an insecticidal soap available at most nurseries and garden centers.

Actually, insecticidal soap is about the only product available that is effective in controlling spider mites. Scale insects or mealy bugs can be removed from plants by using a cotton swab dipped in rubbing alcohol.

Avoid using alcohol on plants with hairy leaves such as African violets and gloxinias.

Heavily infested plants may require the application of a chemical insecticide. There are several insecticides available that will help control houseplant insects. Many of them are available in ready-to-use containers.

It is very important that the plant and insect pest that you plan to treat are both listed on the label.

Whenever insecticides are used, it is important to carefully read and follow all directions and precautions printed on the label.

Unless heavily infested plants are especially valuable, it may be advisable to discard them instead of using heavy applications of a chemical product.

For more information, contact me at the Polk County Extension office in McIntosh at 800-450-2465, or at the Clearwater County Extension office on Wednesdays at 800-866-3125.

If e-mail is your thing, contact me at Source: Carl Hoffman, Stearns County Extension Service.