Winter Pesticide Storage
What, if anything, should be done with herbicides, insecticides and fungicides left over from the summer growing season? If pesticides freeze, will they still be good next year?
The first rule of thumb is to check the product label for storage recommendations and any warnings against freezing, said Clyde Ogg, pesticide safety education coordinator at the University of Nebraska-Lincoln. Most liquid pesticides may be safely stored between 40°F and 100°F.
If a liquid pesticide does freeze, it may be less effective. Apply a degraded pesticide next year, Ogg said, and you have just wasted your time.
Pesticides contain active and inactive ingredients. The active ingredient is what kills the pest. Inactive ingredients include solvents, carriers, or emulsifiers that make the pesticide more efficient.
Due to the inclusion of these hydrocarbon solvents or inert ingredients, the freezing point of many liquid pesticides is lower than 32°F, notes a University of Missouri Extension publication, Temperature Effects on Storage of Agricultural Pesticides. When a liquid pesticide freezes, the active ingredients can separate from the solvents or emulsifiers, causing the emulsifiers to become inactive, crystalize, and coagulate, breaking down the original product.
If frozen, some pesticides can be thawed naturally at room temperature, but never with a flame or heat. Make sure the container has not cracked. After thawing, roll and shake the container to resuspend the contents.
If crystals are still present after thawing, the pesticide should not be used as it will be ineffective. Rather, properly dispose of it according to label directions.
Generally, wettable powders and granules aren’t affected by low temperatures. Moisture, though, can cause caking that may reduce effectiveness. Products formulated in water-soluble packets should not be frozen as they will become brittle and break open.
When storing pesticides, Ogg recommends:
- Don’t store pesticides near heat, sparks, or open flames
- Avoid contaminating other pesticides, water, feed, or fertilizer.
- Keep containers tightly closed in a cool, locked, well-ventilated place away from children and pets.
- Store in original containers only.
- If storage information cannot be found on the label, contact the pesticide manufacturer.