October 31, 2015

1 - Insects that come indoors when houseplants are brought in for the winter may be managed by chemical treatment and traps.

Yard and Garden October 31, 2015


I brought my houseplants in for the winter last week. I almost immediately noticed a lot of insects in my house. Is there some safe way to eliminate these insects in my house? Do I need to use pesticides on the plants? Can I spray safely indoors?


Insects are common hitch-hikers on plants that are brought in from outdoors. Often they are not numerous because predator insects have kept the number of pest insects at low levels while they were outside. Once the plants are brought indoors they may be removed from the source of predators controlling the pests. These pest insects can then begin to rapidly increase in numbers and impact on the houseplants. Since you said that you have only had the plants indoors for a week, it is likely that the pest population was already large, or perhaps some of the insects you are seeing are small predator insects that came in with the plants and pest insects. If these are predators that came in with the plants, they may help manage the pest population at low levels for a while until the predators die off. They are less adapted to life indoors than the pests.

Many gardeners treat their plants with insecticides (organic or non-organic products) before bringing plants indoors. This would reduce the number of both pest and predators brought indoors. If some of the pests persisted they would rapidly increase in numbers even before the plants were brought indoors. Now that they are indoors they quickly become evident.

While the weather is still warm enough during the day you can take the plants outside to treat them with insecticides. The appropriate product to use will depend on your preference for organic or non-organic products and the type of insects you are seeing.

Aphids, scale insects, and mealy bugs are common houseplant insects. Aphids reproduce very rapidly and can greatly impact plant health and growth. Apids, scale insects, and mealy bugs can be treated in a number of ways fairly safely. You can use insecticidal soap solutions (protect furniture, carpets, draperies, and other materials from the soap spray), diatomaceous earth, and pyrethrum / pyrethroid containing products can be used to manage aphid and mealy bug populations indoors. Scale insects are more difficult to control indoors. Insecticidal oil products applied directly to the scale with cotton swabs may kill scale insects or allow you to physically rub the insects off the plants. When using pest control products be sure read, understand, and follow the directions on the product label. This advice is valid for both organic and non-organic pest control products.

Aphids, mealy bugs, and scale insects spend most of their life on their host. Winged forms develop rarely, but they can form and become nuisances around a home. There are other insects that may come in with your plant that also produce winged forms. Fungus gnats are common household nuisances associated with houseplants. The flying forms of houseplant pests may be managed in another manner. Sticky traps, modern versions of fly paper, may be used to trap them. There are effective "black light" insect attractants with sticky traps that can capture small flying insects such as fungus gnats, winged aphid forms, and winged forms of scale insects and mealy bugs. There are indoor versions of black light traps with electrified grids to electrocute larger flying insects. These are also useful when moths, flies, and other larger flying insects invade homes. Mine has even killed mosquitoes. The use of traps can reduce the need for insecticide application to protect houseplants through the 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.


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

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