By Cheryl Alberts

What should be done with herbicides, insecticides and fungicides left over from the 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, says Clyde Ogg, pesticide safety education coordinator at the University of Nebraska-Lincoln. Most liquid pesticides may be safely stored between 40 and 100 degrees F.

If a liquid pesticide does freeze, it may be less effective. Apply a degraded pesticide next year, and you have just wasted your time, Ogg says.

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 degrees, according to 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 re-suspend 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 the following:

• 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.

Storing your sprayer for winter
What about your sprayer? To keep your sprayer in good condition, follow these suggestions for sprayer storage from the Nebraska Extension publication, Cleaning Pesticide Application Equipment, G1770;

• Wear personal protective equipment.

• Before storing the liquid sprayer for winter, ensure it is completely empty and clean. As much as 15 gallons of product can remain in the tank after it's been emptied, due to the volume in the lines and filters.

• When storing, add one, and up to five, gallons of lightweight oil such as diesel fuel or kerosene before final flushing. This applies a protective coating on the inside of the tank, pump, and plumbing.

• Store in a clean, dry building. If the sprayer must be stored outdoors, remove hoses and store these inside where they will be protected from ultraviolet light.

• For sprayer trailers, put blocks under the frame or axle to prevent flat spots on tires during storage.

Alberts is pesticide safety education program project coordinator at the University of Nebraska-Lincoln. This report comes from UNL CropWatch.