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What's the shelf life of garden chemicals?

If you can't remember when you purchased the fungicides, herbicides, and insecticides you're using in the garden this spring, you may be applying products that have lost much of their effectiveness.

Chemical companies formulate their products to last in the container for a minimum of two years; the Environmental Protection Agency (EPA) only requires that they last one year. Under ideal storage conditions, many chemicals remain effective for 7 to 10 years or longer. Exceptions are biological pesticides, such as Bacillus thuringiensis. Since these are made from living organisms, they're much more vulnerable to temperature extremes. Above 90 |degrees~ shelf life is about a month. When stored in cool, dry conditions, liquids can last for a year, powders up to three years.

But few garden chemicals are stored under ideal conditions. Exposure to light, high humidity, and temperatures above 90 |degrees~ greatly reduce their longevity (for storage of specific chemicals, follow label directions). Since manufacturers can't control conditions once the products are sold, they limit their guarantees.

Pesticides don't spoil suddenly. Instead of being 100 percent effective after several years, they may be only 70 to 80 percent effective. But even this level may be more than adequate.

Unfortunately, no foolproof way exists to determine if a pesticide will still do the job. Chemical companies generally don't date their products (they use lot numbers), so a consumer can't tell the pesticide's age. The only test is to use it.

What to do with leftover pesticides

Inventory your chemical cupboard. As long as the EPA hasn't banned a product or restricted its use (limiting it to certain plants or pests or professional application), it's environmentally safer to use it up as needed according to label directions than to throw it away.

Never pour pesticides down a drain or dump them onto the soil.

If you're in doubt about the safety of a product, call the EPA (look under government listings in the telephone book).

After the chemical is applied, exposure to microorganisms, organic matter, rainfall, sunlight, and wind help break it down. When a container full of pesticide is discarded and buried in a landfill or toxic waste dump, the pesticide can take years to degrade because it's less subject to biological activity and ultraviolet light.

But don't use a product just to get rid of it. Apply it only if there is a problem, and use it only on plants and pests listed on the label.

Even if you think the product may have lost some of its effectiveness, don't exceed the recommended dosage. That could leave unhealthy residues on food crops or burn foliage.

For concentrates and wettable powders that must be diluted, mix only the amount you can use that day. Once a product is diluted, its lifespan is very limited. After applying the chemical and waiting until the recommended time between applications has elapsed, you can judge its effectiveness.

Disposing of restricted or banned pesticides

If your cupboard contains a product with chlordane, DDT, lead, or mercury, dispose of it according to local ordinances.

Many cities have household toxic waste cleanups. To find out what to do in your area, call your city's waste disposal service or fire department, or county agricultural commissioner's office.

Buying and storing pesticides

Buy only the amount you can use in one season. Don't be swayed by a sale or economy-size prices. Also, try to find out how long the chemical has been on the store shelf (make sure it hasn't been stored in some back room for a while). Mark containers with the date of purchase.

After use, tightly close containers. Store in a cool, dark, dry place, such as a cupboard in the garage or shaded storage shed (not a metal shed). Keep storage doors locked when not in use. Don't keep pesticides indoors. If possible, avoid storing them in areas with extreme temperature fluctuations; the ideal range is between 50 |degrees~ and 75 |degrees~.

A gentle insecticide

When insects like aphids and whiteflies start damaging your garden plants, you can fight back by applying a gentle but effective insecticide. Chances are you already have the ingredients in your kitchen.

The following formula is based on the one used in Sunset's test garden at Menlo Park, California. You'll need a 1-quart, pump-action plastic spray bottle. To the spray bottle, add 1 teaspoon of mild dish-washing liquid and 1 teaspoon of cooking oil, add water to make 1 quart, and shake to mix ingredients. The oil suffocates existing insects, and new arrivals are repelled by the soapy solution's taste; the cooking oil also makes it stick to the leaves.

Spray the affected plants, making sure to wet both the tops and undersides of the leaves. If rain or sprinkler water washes the solution off plants, spray again if insects persist. Monitor plants for any signs of leaf burn.
COPYRIGHT 1994 Sunset Publishing Corp.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1994 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Special Issue: Spring-Summer 1994 Garden Guide - Planting & Maintenance Guide; includes related article on how to make a gentle insecticide
Date:Mar 22, 1994
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