Storing and Using Pesticides

Shelf Life

Use fresh products whenever possible. Buy only what is needed for the current year and mark the purchase date on the container. The shelf life of pesticide products is influenced by the formulation, the container type and the  storage conditions (temperature, humidity). As a rule, an unopened container stored at moderate temperature will remain effective for 2 to 5 years. Under poor storage conditions, the formulation and/or the active ingredient can deteriorate, separate or solidify. To prevent damage to equipment, mix a small amount of any suspect material in a jar first to see if it mixes properly. The only way to know if the active ingredients have been affected is to treat a pest infestation and monitor the results.

Alkaline water

The pH of water used as a dilutant can affect the life of the active ingredient in solution. Many insecticides will degrade rapidly in alkaline water (pH greater than 7). Some ingredients, such as malathion and trichlorfon (Dylox), are particularly sensitive and degenerate within a few hours after being diluted. High temperatures increase the rate of degradation in alkaline water. Many product labels suggest proper pH ranges for water.

To prevent degradation of ingredients in a mixture:

  • Mix the pesticide with water and spray immediately or within a few hours. Never allow pesticides to remain in solution overnight before spraying.
  • Use an acidifier to adjust the ph of the water to neutral (ph = 7) or slightly acidic. Although vinegar is frequently recommended for lowering pH, commercially available buffers are better suited for this purpose.

Temperature effects

Temperature alone can affect pesticide effectiveness. Organophosphate insecticides work better at higher temperatures (except for DDVP which is best used at about 50 to 72 degrees F). Synthetic pyrethrum derivatives (sumithrin and resmethrin) are less effective at high temperatures. Many product labels suggest temperature ranges for making applications.

Look for the following symptoms which indicate that a pesticide may have deteriorated:

Emulsifiable concentrate (EC) No milky formation; insoluble sludge or layers in the mixture.
Wettable Powder (WP) Product is lumping and some of the material won’t go into suspension.
Dust Excessive lumping
Granular Excessive lumping
Aerosols Obstruction in opening
Smoke Difficult to light, lumping

* from Langhans, R. W. 1980, Greenhouse Management, Halcyon Press of Ithaca, Ithaca, New York, 239 pp.