Gardening Laidback Gardener Tip of the Day Pesticides

Choose a Pesticide With the Narrowest Possible Spectrum

Most pesticides sold in garden centers have a broad spectrum: they indiscriminately kill anything within their range.

The ideal pesticide would be the one with an extremely narrow spectrum, acting on only one enemy and nothing else. Thus, the impact on the environment would be minimal: a single insect, disease or plant would be eliminated without negatively affecting anything nearby.

Right now, though, most pesticides on the market are quite the opposite: they are broad spectrum products. This includes insecticides that kill all insects, even ladybugs and bees; herbicides that eliminate all broadleaved plants including the lilies and foxgloves in your flowerbed; and fungicides that attack pretty much any fungus, even the ones needed to decompose plant debris and dead leaves.

Btk is a bacteria that only kills caterpillars.

However, there have been some interesting breakthroughs into more specific compounds that affect only a limited range of pests. Think of the highly popular Btk (Bacillus thurigiensis kurstaki), which only kills caterpillars (moth and butterfly larvae) and nothing else, and of beneficial nematodes (Steinernema, Heterorhabditis and others) that only infect grubs, maggots and other insect larvae that chew on plant roots underground.

A lot of very promising research is being carried out in this area. One day, we’ll probably be able to obtain an organic pesticide that only acts on goutweed (Aegopodium podagraria) or red spider mites and absolutely nothing else. That will certainly make gardening easier while reducing any negative environmental effects.

In the meantime, however, apply any pesticide, even an organic one, with precaution, as there is always risk of collateral damage.20170207a

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 “Choose a Pesticide With the Narrowest Possible Spectrum

  1. Melody Brinigar - Winfield, Kansas

    We have recently been invaded with purslane. Any suggestion on getting rid of it?

    • It’s an annual and starts up each year from seed. It absolutely requires sun to germinate. If you can mulch the soil, that will stop it dead… next year. In a lawn, mow higher and do what you can to keep the lawn dense so it can’t germinate.

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