IN GOOD THYME "How to deal with pesky houseplant pests

My grandmother Elisabeth had a passion for house plants. Tropical foliage thrived in every room of the house. Her bedroom, however, with its big east-facing windows, was a miniature rainforest. There were several varieties of blooming begonias, a squat, shiny jade plant, philodendron, tradescantia, elephant ears and more.

Every Thursday morning she filled the big claw-foot bathtub with about two inches of water, then carefully carried each of her 15 or more plants down the hall to the bathroom for their weekly spa, which included a gentle spraying with tepid water. Anyone who entered the bathroom on Thursday stepped into a humid jungle filled with the sweet scent of moist earth.

In the afternoon when school was out, my sisters and I would help lift the plants from the tub, wipe the pot bottoms to minimize drips, and carry them back to grandmother’s room. One of my less pleasant childhood memories is of lugging a huge crown of thorns plant down the hall, trying not to become impaled on its wicked barbs. Inevitably I managed to stab myself, and have disliked those plants ever since.

Grandmother’s plants were a healthy lot. I can’t remember there being any problems with insects or disease. In fact, most of the plants outlived Elisabeth and are still thriving under her grandchildren’s care. I can’t prove that their vigor had anything to do with weekly trips to the bathtub, but they were certainly clean. And keeping plants clean is the best way to ward off the insects that can harm them.

The tropical and sub-tropical plants we raise in the artificial environments of our homes need water, food, sufficient light and good soil with proper drainage. They also need to be observed for signs of insect infestation. The pests most likely to attack your indoor plants include spider mites, aphids, scale, mealybugs, white fly and fungus gnats.

Spider mites are so tiny you may not notice them until you see the damage they do. Leaves begin to look pale or ashy. There may be fine webbing between stems and leaves or on the undersides of leaves. First aid for spider mites is soap and water. Gently wash all parts by hand using about a tablespoon of dish soap to a gallon of lukewarm water, or apply commercial insecticidal soap according to directions. You may have to repeat this procedure weekly for the month it could take to eliminate all mites.

The same method makes short work of aphids, but it shouldn’t take more than an application or two to quell these soft-bodied suckers, often detected by the sticky “honeydew” they produce.

Scale insects look like tiny bumps usually found on stems and underneath leaves. The bumps are actually protective shells that effectively repel water and even insecticide as the bug sucks the life out of your plants. You can readily dispatch them, however, by dabbing each one with an alcohol-soaked Q-Tip.

Mealybugs look like tiny pinpoints of cotton, often found on stems, leaf axils and undersides of leaves. They, too, have a protective coating that repels sprays, so if you use the soap and water solution or insecticidal soap, add a small amount of laundry detergent per gallon. It acts as a wetting agent that penetrates the insect’s coating. Another option is to spray or hand apply a small amount of rubbing alcohol dissolved in water. Mealybugs often pile on top of each other in layers of two or three, so make sure your spraying or dabbing is forceful enough to penetrate the pileup.

Deadly in numbers and difficult to control, white fly is another story. In a greenhouse setting, an excellent biological control is the small predatory wasp, Encarsia formosa, available through some nurseries and via the Web. Inside the home there are a few things you can try, but you must be persistent. Neem oil, a botanical insecticide, is helpful, as are yellow sticky traps placed near the affected plants. Both are available at nurseries.

Then there’s the fungus gnat, a most annoying creature. You may notice these tiny black flies rise from the soil when you water. Their maggot offspring live in the soil, feeding on decaying organic matter and sometimes, the roots of plants. Fungus gnats are often found where plants are overwatered and drainage is poor. Allow the surface of the soil to dry between waterings, and don’t use incompletely composted material in your potting mix. Sticky traps are somewhat effective. In severe cases, try drenching the soil with insecticidal soap, then watering thoroughly.

There are also many home remedies for eliminating house plant pests, ranging from jalapeno spray to tobacco juice. If you have a good one to share, please let me know.

Garden questions or comments? Call 675-6611 or e-mail Mariana Graham is a WSU-certified Master Gardener and a member of Garden Writers Association of America.

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