In the Garden:
Northern & Central Midwest
January, 2006
Regional Report

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Inspect your houseplants closely for insects because they might look as healthy as my African mask plant, which has been hiding a large population of spider mites.

Houseplant Pests On the Rise!

I was admiring my seemingly healthy kentia palm recently when I noticed small, shiny spots scattered over the leaves. A closer inspection showed me the beginnings of scale, a common houseplant pest that is very hard to get rid of. The sticky spots are the residue the scales secrete as they suck out plant sap, and they are a good diagnostic tool. This honeydew is harmless to the plant, but the scales that are feasting on the plant can cause its deterioration.

Insect pests will not get out of hand if your plants are in good health and get the care they need. But all it takes for a spider mite population to get out of control is to let the humidity levels drop briefly. All it takes to get a fungus gnat explosion is to overwater a plant even a couple of times (to say nothing of the other types of problems this causes). If you familiarize yourself with the damage insects cause, though, you can use some of the simpler, less toxic methods for getting rid of them.

If your plant doesn't look quite right, start checking. My African mask (Alocasia x Amozonica 'Poly') started looking a bit off, and a closer look revealed an infestation of spider mites. The plant's leaves are paler than usual, and I noticed very fine webbing on the backsides of the leaves. Mites are too small to see easily, but their damage is distinct. Take a piece of white paper and tap the plant. If the specks that fall on the paper move, you have mites. If they don't, it's just dust.

If the new growth on a plant is distorted, you may have thrips, aphids, or some other pest that is preventing the natural flow of sugars, water, and hormones to all parts of the plant. There may also be a disease problem.

Sprays and Showers
Although the discovery of scale on my kentia palm was disheartening, I know I can keep the population to a tolerable level even if I can't get rid of all the insects. I spread out a plastic drop cloth and sprayed the plant to dripping with horticultural oil. This lightweight solution smothers most of the adult and immature scales. I will repeat the procedure in ten days which will probably take care of the remaining pests. And, I will do the same thing to my African mask.

The simplest way to dispatch most of the fairly immobile pests is to wipe down the leaves regularly or bathe the plant in the shower. And if you notice a pest on one plant, chances are good that you will find it on others nearby. Putting the plant in the shower and dousing it with horticultural oil or insecticidal soap will eliminate many pests in a non-toxic, harmless manner.


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