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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 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[deg], 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[deg] 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. Even if you remember when you purchased it, you probably don't know how long it sat in the store. The only test is to use it.

What to do with leftover pesticides

First, 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.

If you're in doubt about the safety of a product, call the EPA (look under government listings in the telephone book). Never pour pesticides down a drain or dump them onto the soil.

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, it 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 only on plants and pests listed on the label. If you can't use a pesticide up yourself, give it to someone who can, such as a neighbor or garden club member (or follow the disposal procedure below). 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 the effectiveness and reapply if necessary The worst possibility is that the product won't control the problem and you'll have to buy a replacement or another product.

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

For future purchases, buy only the amount you can use in one season. Don't be swayed by a sale or economy-size prices unless you can share with someone. Also, try to find out how long the chemical has been on the shelf (make sure it hasn't been stored in some back room for a while). Mark with 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[deg] and 75[deg].
COPYRIGHT 1989 Sunset Publishing Corp.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1989 Gale, Cengage Learning. All rights reserved.

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Publication:Sunset
Date:May 1, 1989
Words:731
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