Using old pesticides may be perilous to your plants

Pesticides that are past their shelf life may be ineffective and could cause plant phytotoxicity.

An example of storage information on a pesticide label.

An example of storage information on a pesticide label.

Now that the commercial production season is well underway, greenhouse growers may be dusting off old pesticide containers to use these chemistries to control pests. Before you do so, make sure you aren’t posing problems for your plants and your pocket book.

Stored pesticides will lose their effectiveness over time. They may break down (change chemical composition) into products that may no longer have pesticidal properties or change form. like producing flakes, crystals or caking, that make it difficult if not impossible to mix and use in sprayers. If an aged product breaks down and you spray it on your crop, you may see phytotoxicity symptoms. So, not only may the product be ineffective, but it can directly damage your crop, impacting your profitability.

The shelf life of a pesticide is the timeframe that the pesticide can be stored and still be effective. Nearly all pesticides have a limited shelf life, which is affected by how the product is stored, the chemistry formulation and container integrity. For details on proper storage of chemicals, see the Michigan State University Extension article “Michigan pesticide storage and handling guidelines for greenhouses.” In general, pesticides should be stored in their original, tightly sealed containers and should be kept in a dry (40-50 percent relative humidity) and moderately temperate (55-65 degrees Fahrenheit) room year-round that is not exposed to direct sunlight. Always read the pesticide label for additional storage information (see photo).

The pesticide label may indicate the shelf life of the pesticide. However, the U.S. Environmental Protection Agency (EPA) only requires an expiration date on the label in certain circumstances. In order for a formulation to obtain an EPA registration, the manufacturer must supply data for a one-year stability study to demonstrate that the formulation does not significantly change chemical composition over the period of a year. If the results of this study show the product will not remain stable for a one-year period, then an expiration date may be required.

In the absence of an expiration date on the pesticide label, if you have stored the product properly (i.e., kept it from excessively cold or hot temperatures and kept it dry), assume a two-year shelf life. In order to make the most of your pesticide stock, only order the amount of product that you will use each year. When you purchase new product, write the date it was received on the outside of the container and use older product first. When using older product, inspect the product and the container before use. For wettable powders, dusts or granules, look for caking or clumping of the material. For oil-based chemistries, look for the formation of sludge or separation of the solution. For emulsifiable concentrates, break down may have occurred if the addition of water does not produce a milky solution. For aerosols, check to see if the nozzle is clogged or if the propellant no longer works. These signs or damage to the container may indicate that the product has been compromised or expired.

When in doubt about the efficacy or longevity of a product, contact the manufacturer or dealer. If you determine the product needs to be disposed, contact the Michigan Department of Agriculture and Rural Development Clean Sweep Program. This program is free to use and is the safe way to properly dispose of chemicals.

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