Magazine article Sunset

What's the Shelf Life of Garden Chemicals?

Magazine article Sunset

What's the Shelf Life of Garden Chemicals?

Article excerpt

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. …

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