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Archive for Saturday, November 27, 2010

Garden Calendar: What’s bugging your houseplants

November 27, 2010, 12:00 a.m. Updated 12:00 a.m.

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Good news about insects and mites that feed on houseplants: Most of them are easy to control, once detected.

Mini Cattleya of Corsage orchid

Mini Cattleya of Corsage orchid

The bad news: They are sometimes hard to see. Also, plants that are most favored for their beauty are often the most susceptible to injury. That means they have to be checked a little more often.

In case you are wondering, I still follow the philosophy of growing things that are easy to grow. Just as my yard is filled with well-adapted, low-maintenance species, my home and office are filled with plants that generally require little care.

I also recommend evaluating how much you like a plant if it has repeated pest problems. Sometimes you have to be willing to say goodbye to a plant. (And giving an insect-ridden plant to a friend may cause you to say goodbye to your friend.)

All that said, I have a soft spot for a few plants, particularly orchids. Sometimes a little insect control is worth it, and right now we are fighting soft scale insects.

Back to easy-to-grow selections: Pest-resistant plants can pretty much be ignored. I doubt there is a sansevieria (snake plant or mother-in-law’s tongue) that has ever had an insect feed on it. Spathiphyllum (peace lily) has more problems with light and water than any little creepy-crawlies.

Ficus, palms, and even schefflera offer more challenges when it comes to insect pests, though. Check these plants regularly and watch for even subtle changes in growth.

The most common houseplant pests are aphids, mealybugs, scales, thrips, spider mites, fungus gnats, and whiteflies. The first five are easily controlled by a soapy water bath. Experts recommend using two teaspoons of mild detergent to every gallon of water and rinse the solution from the plant after washing.

Sago Palm

Sago Palm

If plants are too large to move or infestations are unmanageable, use insecticidal soap or another botanical insecticide according to label instructions.

Whiteflies can be controlled with yellow sticky cards that are available at most garden centers. Thrips are attracted to blue sticky cards in lieu of the soap water bath. Fungus gnats are best controlled by allowing soil to completely dry out between waterings.

What to look for:

Aphids and mealybugs are large enough to see and produce honeydew that coats the leaves and sometimes attracts ants. Honeydew is a nice name for insect excrement and is a clear, sticky substance.

Aphids are one to six millimeters long and pear-shaped with visible antennae and bent legs. Mealybugs are a little larger than aphids and are oval with a white, waxy coating on their bodies.

There are two common types of scale insects: soft scales and armored scales. Soft scales produce honeydew like aphids and mealybugs, but they look like tiny dinner plates. Armored scales also look like tiny plates and may be harder to control.

Whiteflies look like tiny moths. Their four wings are coated with a waxy substance and their populations often explode in a short time. A handheld vacuum is another effective way to remove whiteflies.

Fungus gnats look like other gnats but spend their days hovering just over the potting soil surface. Females like to lay their eggs in moist soil.

For thrips, you are more likely to notice black drops of excrement on plant leaves. They are slender insects, just a little larger than aphids, and the adults are winged.

Spider mites are the hardest to detect. Leaf damage from spider mite feeding is referred to as stippling or bronzing. The discoloration occurs from the loss of chlorophyll from mites sucking the juices out of the plant. If you suspect spider mites, hold a piece of plain white paper under the plant and shake it. You can usually see tiny black specks (fallen spider mites) running across the paper.

Let us hope the orchid stays scale-free the rest of the winter. It’s just getting ready to bloom.

Jennifer Smith is the Horticulture Extension Agent for K-State Research and Extension in Douglas County. She can be reached at 843-7058.

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