Protecting Houseplants from Pests

The cold weather may be keeping you away from your backyard garden, but it’s a wonderful time to focus on your plants indoors. Winter is also when houseplants are especially susceptible to issues like pests. The shorter days mean a reduced photosynthetic output, which in turn means plants can produce fewer protective chemicals. Reduced humidity levels indoors can also cause tropical houseplants stress, increasing their susceptibility to pests.

To avoid indoor pest problems with any new plants you acquire, the Kemper Center for Home Gardening recommends isolating them for two to three weeks.

Mealybugs

If you do have a pest problem, some of the most likely culprits are:

  • Mealybugs, a waxy, white, cottony pest that are usually found in clusters along leaf veins. Plants infested with mealybugs become weak, may wilt and turn yellow, and eventually die.
  • Thrips are rarely seen due to their size. They cause flowers or leaves to develop silvery streaks. Heavily infested leaves appear brownish or silvery, and growing points may become contorted.
  • Scale, small, piercing-sucking insects, often go unnoticed on indoor plants. The first signs of a problem are yellowing or wilting leaves that may eventually drop. Leaves may also be covered with a clear sticky substance called honeydew.
  • Spider mites are so small that the sign is generally a plant that looks dull or in poor health. Leaves may appear stippled and curled. Fine webbing may also be evident under the leaves or between the leaf and the stem. When a leaf or branch is tapped over a white sheet of paper, small specks that appear as dust or pepper may be seen to move.

The first step to dealing with mealy bugs, scale and spider mites is to remove the pests from your plant. A strong stream of water is recommended for spider mites and mealy bugs. Scale can be removed by hand with a discarded toothbrush, or with a cotton swab soaked in isopropyl alcohol. Prune out heavily infested portions of the plant.

Thrips pupa (Thysanoptera) on flowering maple (Abutilon)

For thrips, which often attack plants in the Gesneriaceae family, like the African violet, and Commelinaceae family, like the wandering Jew, keep the plant well moisturized to limit damage.

With any pest problems, the next step is to try an insecticidal soaps, which are considered nontoxic to humans and pets. You can also try horticultural oil sprays, which suffocates insects.

Chemical insecticides that are registered for use indoors are available, but be sure to read the label carefully. As a general rule of thumb, Kemper staff recommend trying the most organic approach first and turning to chemicals as a last resort.

After you’ve gotten rid of pests, be sure to regularly inspect your plants to limit future problems. Pest problems caught early are easier to control.

More information about common problems for indoor plants can be found in this guide.

The Kemper Center is also always here to help! You can email questions to plantinformation@mobot.org or call the Horticulture Answer Service, from 9 a.m. to noon Monday-Friday, at (314) 577-5143. You can also bring your questions to the Kemper Center in person from 10 a.m. to 3 p.m. Monday-Saturday and get advice from a Master Gardener.

More plant tips, including bloom times and tips by month, can also be found on the Kemper Center’s website.

Catherine Martin
Public Information Officer

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