Laidback Gardener Tip of the Day

Learning to Live with Spider Mites

août 29
Photo: Wikimedia Commons

The red spider mite (also called the two-spotted spider mite, Tetranychus urticae) is widespread in nature: in fact, it is found almost everywhere. Outdoors, it’s found in both in temperate and tropical climates and indoors, it’s common on houseplants. It is said to be polyphagous: that is, it attacks a wide range of plants, including most vegetables and herbs and many ornamental plants.

The red spider mite is a tiny little eight-legged pest (it’s a not an insect, but a mite, as insects have six legs). it is barely visible to the naked eye. On a plant, it will look like dust, but dust that moves. You need a magnifying glass to see it well. It can be red, as the name suggests, especially in cool weather, but will more likely be beige or pale green. It is marked with two dark spots, but they are only visible when it is a pale color. The red spider mite pierces the leaves and stems of plants and laps up the sap that leaks out. This causes, at first, a general yellowing, often a bit mottled. As the infestation advances, “spider” webs appear along and between leaves and stems. These will appear dusty due to the presence of moving spider mites.

Despite being such a common and prolific pest, red spider mites are surprisingly easy to control. In nature, a good heavy rain will almost completely wipe out a colony. That’s why is is mostly a problem when rain is absent. In your garden, simply spray the affected plants with a strong stream of water and the problem will be solved. Indoors, place infested houseplants in the shower and rinse both sides of the leaves. It also responds well to insecticidal soap and pyrethrins… but why bring out the big guns when water will do?

On the down side, as long as the conditions that contribute to its development remain in force (hot, dry air and no rain), you’ll need to repeat the treatment occasionally, because it is very difficult to eliminate spider mites completely. A few always seem to survive to start the infestation again. So, aim for the control of spider mites, but forget the idea of ​​completely eliminating them: you simply will not succeed.

This is one of those cases where the “15 pace rule”, dear to laidback gardeners everywhere, applies. If, at 15 paces, the plant looks green and healthy, there is no reason to react, even if you’ve see a few spider mites (probably under a magnifying glass, otherwise they’re pretty much invisible). But if you see the symptoms of its presence at that distance (yellow mottling is the first clue, plus spider webbing if the infestation is more advanced), it is time to intervene.

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

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