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The Homeowners Column
What Is the Shelf Life of Pesticides?
Sandra Mason
Extension Educator, Horticulture
slmason@illinois.edu
The garden season is winding down. You may find you have pesticides left over from that battle with the Japanese beetles. How and how long should pesticides be stored? How long can chemicals be kept before they lose their effectiveness?
General Guidelines
1. Pesticides should always be stored out of the reach of children and pets, in a well ventilated cool dry area and under lock and key if possible. Designate and label a cabinet exclusively for pesticides.
2. Always purchase pesticides in a container size small enough to be used within a season or less. This is the best method for reducing storage problems, disposal problems and doubts on pesticide effectiveness. This method may seem somewhat uneconomical. However commonly people will buy new pesticides rather than wonder if the old one is effective which creates a leftover pesticide disposal problem.
3. Mark the purchase date on the container.
4. Always get proper identification of problem before purchasing pesticides. Take a sample to your local Extension office or to the U of I Plant Clinic. Many times other control options are available such as sanitation, mechanical controls or selecting disease resistant varieties. Less toxic pesticides such as insecticidal soaps or horticultural oils may be an option and can be used for a wide variety of insects.
How long a pesticide remains effective depends on the pesticide formulation, length of storage and conditions during storage. Always read and follow all pesticide label directions. There is specific information about the pesticide storage on the label. The following are estimates on the shelf life of various insecticides, fungicides, and herbicides according to a study by Cornell University.
| Pesticide | Shelf life (years) | Comments |
| Sevin, wp | several | flowables will settle |
| Diazinon | 5-7 | |
| Malathion, wp | indefinite | decomposes under high temperatures |
| Captan, wp | 3 | |
| Thiram, wp | 4 | keep dry, below 100°F |
| Dacthal, wp | at least 2 | |
| Roundup, liquid | at least 2 | stable below 140°F, do not freeze |
| Surflan, wp | 3 | |
| Treflan, g | 3 | loss 15-20 % activity when stored at 100°F |
Regularly check the containers of stored pesticides, especially if you have stored them for more than a year. Some pesticides, if stored improperly or for too long a time, will not mix properly and may be ineffective. Watch for the following indications that it is time to dispose of your pesticides:
| Formulation | Signs of breakdown |
| oil sprays | Sludge forms, solution separates |
| emulsifiable conc. - EC | Addition of water does not produce a milky solution |
| wettable powders- WP | Clumping, powder will not mix with water |
| dusts and granules | Excessive clumping |
| aerosols | Generally effective until nozzle clogs or propellant is dissipated |
The following are some suggestions for safe storage:
1. Generally manufacturers recommend storing pesticides no longer than two years.
2. Keep storage temperatures below 100°F and above 40°F.
3. Keep chemicals in original containers and tightly sealed. Be sure that caps are securely tightened on all bottles and cans. Leaky containers should be placed in coffee can with vermiculite or sand for proper disposal.
4. Properly dispose of pesticide products whose labels have been lost or are not complete and legible.
