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Greenhouse Pests
- Greenhouses are a great place for pests, too! -
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Summary: In addition to creating favorable growing conditions for plants, greenhouses are ideal places for plant pests as well. Pests increase rapidly and can be extremely destructive in greenhouses. Learn ways to combat insect and mite pests in home, or hobby, greenhouses using least-toxic methods.
Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)
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 Hobby greenhouses have become popular additions to many home gardens. These enclosures provide a means to start plants earlier in the year and extend the growing season. Greenhouses also are great places to overwinter plants, and during the growing season they provide increased humidty or shade.
Plants growing in greenhouses have a number of pest problems, however, that plants growing outdoors generally avoid. Chief among these are aphids, spider mites, whiteflies, scale insects, thrips and sometimes fungus gnats. See Aphids, Spider Mites, & Scale Insects for information about these pests.
Insect and mite pests are often more severe in greenhouses because the enclosure inadvertantly separates plant pests from their natural enemies that would normally keep them under control. Greenhouse also create favorable environmental conditions for pests as well as plants.
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fungus gnat - an important greenhouse pest
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Greenhouse pest control
To counter the loss of natural enemies, one of the best strategies is to artificially release certain predators and parasites such as lacewings, lady beetles and syrphid flies into greenhouses. This procedure is called augmentative biological control.
The next best strategy is to use least-toxic, biorational insecticides. The best choice in this category for use in greenhouses is insecticidal soap. Insecticidal soap will control most soft-bodied pests like aphids, spider mites and scale crawlers and is virtually non-toxic to you, your plants and any beneficials that you release, if used properly (see Using Insecticidal Soap to Control Plant Pests).
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Lastly, the key to greenhouse pest control is regular and consistant monitoring and prompt treatment when pests are detected. Aphids and spider mites, in particular, can increase to damaging levels very quickly in warm greenhouses.
Control of certain greenhouse pests
Aphids - Predatory lacewings and lady beetles can be released into greenhouses to control aphids, spider mites and scale crawlers (see Beneficial Insects @ Arbico-Organics; search on "beneficial insects"). Insecticidal soap is an effective spray as well and will not interfere with these predators.
Spider mites & thrips - Spray leaves with insecticidal soap. Be sure to treat the undersides of leaves as this is where spider mites often feed.
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Whiteflies - There are a number of natural predators that work well for whitefly control in greenhouses. See the Arbico Organics link above).
Scale insects - Use insecticidal soap to treat the crawler stage. Adult scale insects are very difficult to control with soap sprays but can be physically removed with a cotton swab dampened in insecticidal soap.
Fungus gnats - Treat potting soil with insect parasitic nematodes (see Beneficial Nematodes @ Arbico-Organics; search on "beneficial nematodes"). There are several species of nematodes that can be used for soil insect pests but use Steinernema carpocapsae for fungus gnats. These tiny worms infect and kill fungus gnat larvae but won't hurt plants. Also, yellow sticky card traps (see the Arbico Organics links above) can be used to trap for fungus gnat adults, flying aphids, thrips and whiteflies. Flying insects are attracted to the yellow color and become stuck on the glued surface.
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Mission: To provide accurate, up-to-date and unbiased information for solving common insect and mite problems around your home, business and landscape using least-toxic methods.
Jack DeAngelis, Ph.D.
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Copyright © 2004-... LivingWithBugs, LLC. All rights reserved. Page Updated: 3/4/2010
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