Handling Insect Pests in Your Greenhouse

By Roger Marshall
Published on January 5, 2015
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Yellow sticky traps like this one can help get rid of insect pests like whitefly.
Yellow sticky traps like this one can help get rid of insect pests like whitefly.
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Plants in containers can become rootbound, with compacted, crowded rootballs that lack air and soil. Repotting plants regularly prevents this from happening.
Plants in containers can become rootbound, with compacted, crowded rootballs that lack air and soil. Repotting plants regularly prevents this from happening.
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A neem tree is one of many solutions that can help to drive away unwanted insects in your greenhouse.
A neem tree is one of many solutions that can help to drive away unwanted insects in your greenhouse.
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Roger Marshall covers all aspects of owning and maximizing the potential of a greenhouse in “The Greenhouse Gardener’s Manual.”
Roger Marshall covers all aspects of owning and maximizing the potential of a greenhouse in “The Greenhouse Gardener’s Manual.”

Wanting to get the most out of your greenhouse? In The Greenhouse Gardener’s Manual (Timber Press, 2014), author Roger Marshall provides information on how to choose, heat, irrigate and maintain your greenhouse. This excerpt, which details the best methods for controlling unwanted insect pests, is from Chapter 10, “Controlling Greenhouse Pests and Diseases.”

Buy this book from the MOTHER EARTH NEWS store:The Greenhouse Gardener’s Manual.

Talk to any greenhouse grower and they will tell you that the two worst pest problems are aphids and whitefly. You might also find sow bugs, mealybugs, scale insects, and red spider mites. Larger greenhouse pests include slugs and snails that hitch a ride under the rim of large pots or in the drain holes of larger pots. Although screened windows can keep out butterflies and moths, you may also find a caterpillar or two feeding on your plants. Lastly, rodents can get into the greenhouse. Mice are a common problem and I’ve had groundhogs, skunks, and even a fisher that ate all the goldfish in my greenhouse pond one night when I forgot to close the door.

The best way to control insect pests is to be careful what you bring into your greenhouse. An isolation chamber can be a convenient way to keep new plants separate from the main population of greenhouse plants until you are satisfied that they are pest-free.

Whether to use insecticides is a personal decision. I prefer not to spray pesticides of any kind inside the greenhouse because they can kill off beneficial insects along with problematic ones and I find the effects of the product are multiplied by being in an enclosed structure. I have noticed that the odor of a pesticide in the greenhouse can last several days. Also, continual use of the same insecticide can eventually give rise to insecticide-resistant bugs.

My preference is to take the approach of Integrated Pest Management (ipm). This means I always begin with the least toxic type of prevention before moving on to more drastic measures. I start with barriers and screens to keep out pests, rotate crops, eliminate host plants in the vicinity of the greenhouse, isolate incoming plants, keep the greenhouse clean, handpick pests, and finally, bring in natural enemies such as ladybugs to feed on harmful insects. All these controls can easily be integrated into your greenhouse practice before you need to resort to chemical pesticides.

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