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University of Illinois Extension

Pesticide Shelf Life

March 22, 2012

The shelf life of pesticides is a frequent topic of concern for gardeners, said a University of Illinois Extension horticulture educator.

"'How long is a pesticide good for, and how long should I keep a pesticide?' These are questions I hear quite a bit," said Martha Smith. "Pesticides in general are manufactured, formulated, and packaged to specific standards. However, when stored improperly, they can break down, especially under conditions of high temperature and humidity.

"Dry formulas such as wettable powders (WP) or granular (G) can become caked and compacted. Emulsifiable concentrates (EC) can lose their ability to form emulsions. Some pesticides can actually become more toxic, flammable, or explosive as they break down."

Pesticide formulations that contain low concentrations of active ingredients generally lose effectiveness faster than more concentrated forms. Sometimes a liquid pesticide develops a gas as it deteriorates, making opening and handling containers quite hazardous.

"Certain pesticides have a characteristic odor," she noted. "A strong odor in the storage area may indicate a leak, spill, or improperly sealed container. It may also be a clue that the pesticide is deteriorating because the smell of some chemicals intensifies as they break down.

"If none of these problems are found, chemical odors can be reduced with exhaust fans or by lowering the temperature of the storage area."

Pesticide containers, including fiber and metal drums, pails, cans, bottles, bags, boxes, over packs, and liners, have an important effect on storage and shelf life. If stored for long periods, these containers may eventually corrode, crack, break, tear, or fail to seal properly. The label may become illegible as well.

"If stored in a cool, dry area that is out of direct sunlight, pesticides will generally have an extended shelf life," Smith said. "Protection from temperature extremes is important because heat or cold can shorten a pesticide's shelf life.

"At temperatures below freezing, some liquid formulations separate into their various components and lose their effectiveness. High temperatures cause many pesticides to volatize or break down more rapidly. Extreme heat may also cause glass bottles to break or explode."

One way to ensure avoidance of shelf life or storage problems is to only buy what is needed for one season.

"So many times we buy the sale item because it is a 'deal,'" said Smith. "What we find out is that we only needed a small portion, and now we have to store the leftover chemical."

Before storing chemicals, read the label and follow any specific guidelines listed. Store different groups of pesticides, such as herbicides, insecticides, and fungicides in separate locations within a storage area to prevent cross-contamination from fumes andvapors, as well as accidental use of the wrong type of pesticide.

"Never store chemicals near any type of animal feed," Smith said. "Always store chemicals out of the reach of children, preferably in a locked cabinet."

Source: Martha A. Smith, Extension Educator, Horticulture, smithma@illinois.edu

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