1 - Spider mites are common, but easily managed, pests of houseplants during the winter.

Q.

My Hoya plant and airplane plant are not growing well. I heat my home mostly with a wood stove and the plants leaves are coated with ash and dust. Could that be the problem?

- Rachel O.

A.

I was able to see these plants and noticed that the Hoya plant had some healthy branches and other branches with wilted leaves. Looking more closely I noticed that the leaves on the unhealthy branches were the ones that looked like they were coated with dust. Upon looking even more closely I observed that the coating on the leaves was there because the leaves were coated with webbing that has caught the dust. These plants were infested with spider mites. This is not an uncommon problem for houseplants in the winter. The spider mites have no natural predators controlling them indoors and their population can quickly explode. Damage to the health of plants increases as spider mite populations explode. If the spider mite infestation is not treated, the plants may die.

Airplane plants (also called spider plants) are also very susceptible to spider mite damage. These plants were not as severely infested (yet), but that will change quickly. Other houseplants should be frequently inspected for development of webbing and spider mite populations.

Spider mites are fairly easy to manage, even indoors during the winter. The first line of defense it to put the plants in a sink, shower, or bathtub and give them a shower with a strong mist of water from a pressure sprayer or hand sprayer. This pressurized water will wash the spider mites from the plants and will also wash their webbing from the plants. The webbing protects the spider mites from desiccation and from predators (which are absent indoors). By washing the mites from the plants you reduce their population and their damage. Some will try to climb back up to resume their damage, but many may die in the process. Repeated washing may be necessary.

You can increase the effectiveness of washing by using insecticidal soap when spraying the plants. Insecticidal soap will kill many of the spider mites if it is sprayed directly on them. It will also help wash the mites from the plants. Insecticidal soap can damage some plants, so test it on a small part of a plant a few days before spraying the whole plant. If the plant shows no symptoms of burning or other damage where the soap spray was applied, it should be safe to treat the whole plant. Apply insecticidal soap or other sprays to the plants in the sink or bathtub so that the spray does not damage fabrics in your house. Follow the label directions on the insecticidal soap to proper dilute and apply the product on your plants.

Horticultural oils sprays and Neem oil sprays are also labeled for managing spider mites on houseplants. These can be applied to your house plants in the sink or bathtub as well. Once again, be sure to carefully follow label directions.

Vigilance and periodic treatment with plain water, insecticidal soap, oil sprays, or rotating between these treatments should allow your plants to survive and prosper this winter.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

Links:

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.

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