Crop Rotation Confuses Plant Pests

013.KWhen planning your garden, remember that insects have great difficulty locating their favorite plant when you move them around every year. It’s as if you changed apartments annually without leaving a forwarding address in order to shake off your creditors (no, I’m not speaking from personal experience here!). Pests honestly don’t know where to look. Most insect pests, for example, lay their eggs or overwinter as pupae in the soil at the base of the plant that fed them the previous summer. Imagine their confusion when they wake up in the spring, ready to chomp down, but find nothing to eat nearby?

Rotation also is very effective in reducing disease in the garden.

Diseases reproduce mostly by spores and they usually overwinter in the foliage of the affected plant or in the ground at its feet. But while insects can at least start looking for a new host plant and sometimes succeed in locating one (although rotation means not all will be successful), the poor spores, which have no eyes or nostrils or even an effective means of locomotion, are truly lost. They can only rely on the wind to carry them to their host and the wind is unreliable. Proper crop rotation is therefore very effective in preventing diseases on vegetables!

Rotate Families Too

Some vegetables in the cabbage family.

When considering crop rotation, you need to take one other detail into account: plant pests are often specific not to a single plant, but to a whole family of plants. That’s why tobacco mosaic virus can attack any plant in the Solanaceae family (tomatoes, peppers, eggplant and even petunias and nicotianas… and the latter are not even vegetables!). And the cabbage butterfly will attack, quite indiscriminately, any member of the cabbage family (cabbage, cauliflower, Brussels sprouts, broccoli, mustard, etc.). So, when doing your crop rotation, you also do not put plants of the same family in a spot where one of its members grew the previous year.

Rotate over 4 Years

Insects are the easiest to control by crop rotation. If they don’t find a host plant rapidly in very next year, they die. You could use a two year rotation if only insects were involved.

Diseases, however, are pernicious: the spores can survive for more than a year in the ground, waiting until their favorite plant – or a family member – returns. That’s why a four-year rotation is generally recommended: most diseases will be gone after 3 fallow years.

So there you have it: crop rotation is simple, Just avoid planting the same vegetable, or other plant of the same family, in the same place for at least 4 years. That way you can help thwart both bugs and diseases.

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.

2 comments on “Crop Rotation Confuses Plant Pests

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