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Spokane, Washington  Est. May 19, 1883
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Gardening: Organic pesticide can help as last resort

This is the third and last in a series of articles on organic gardening. I am going to end the series with a general discussion on organic pesticides.

And for a very good reason.

If you have built healthy soil, are using mulches to keep down weeds, are using good growing techniques and planting disease resistant varieties, you probably won’t need to use them at all. This is how integrated pest management works. Chemicals are always the last resort whether its organic or conventional gardening.

If you do have an insect or disease problem, it is important to have the pest or disease identified properly. You may be dealing with a beneficial insect you want to keep. The WSU Master Gardener Plant Clinic will help you correctly identify the problem and provide the proper, research-based control methods to use.

If you have to use an organic chemical, buy it from an independent garden center or other specialty garden store. They are likely to carry a broader range of organic chemicals and can tell you how each one works. Our best resource locally is Northwest Seed and Pet. Online resources are fine if they provide good description of the chemical’s mode of action.

To be assured you are getting approved organic pesticides, always look for the Organic Materials Research Institute’s logo on the product. OMRI has lists of approved products on its website. Always read and follow the label directions.

One of the best pest control sprays is just that – a hard spray of water that dislodges pests from the plants and breaks up their breeding cycles. This works well on aphids and spider mites.

Insecticidal soaps and neem oil are popular organic pesticides that control a wide range of insects and larvae. These commercially prepared sprays contain soaps that break down the protective layer of waxes and oils on the insects which dehydrates them and they die.

If caterpillars or larval stages of insects are a problem, sprays containing the bacteria spinosad or Bacillus thuringiensis (Bt) work very well. The larvae ingest the bacteria, which then attacks their internal systems before they have a chance to mature. Last summer, I used a Bt-based spray on a huge population of potato bugs and never found a larva after a week.

Other types of organic pesticides include diatomaceous earth and kaolin clay. Diatomaceous earth is made up of tiny silica-rich fossils that shred an insect’s skin, killing them. Kaolin clay is used to dust fruit to camouflage it from codling moth.

What about homemade or folk treatments for pests and diseases? There are recipes all over the internet. They use such things as dish soap, vinegar, hot pepper, Epsom salts and the like. Unfortunately, most of these recipes have not stood up in research testing. The mixes aren’t reliable because there is so much variation in the recipes, their efficacy can’t be guaranteed. Many of the ingredients are not naturally occurring compounds so they don’t qualify to start with.

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