Scale Insects: Naughty, Nice or Neutral?

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The best organic control of scale is a horticultural oil spray. The oil sprays are highly refined vegetable or petroleum products. Scale breathe through pores in their skin (again, similar to aphids); the oil plugs up the pores, suffocating the insects. If used in early spring on outdoor plants, it will suffocate scale embryos, too, and early application should prevent the mold from forming.

When you apply the oil, cover all plant surfaces and the ground within the drip line. If an outbreak occurs in summertime, wait until temperatures drop below 90 degrees to apply the oil. Some indoor and outdoor plants may suffer leaf burn from these oils, so use them with caution until you know how your plant responds. Or you can also research potential side effects before you treat the plants; information is widely available on the Internet or from your local Extension office.

If your houseplants show signs of scale any time of year, minor infestations can be treated by rubbing the scale off with a soft cloth dampened with water, or water combined with a spray oil or a mild dish detergent. Dabbing the scale with household rubbing alcohol works, too. Use a cotton swab or small art paint brush, and keep the alcohol off the plant as much as possible.

Once a plant is infected, it will need even closer monitoring, and heavy infestations may even force you to remove and dispose of the infected plant or plants. It pays to keep an eye out for these pests, and to work to control them when their numbers are small before it’s too late.

Houseplants most commonly attacked by scale, in addition to citrus, are schefflera, ferns, palms, ivy and ficus.

— John Stuart

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