Dealing with Leftover Pesticides

Homeowners often ask what are their options concerning leftover pesticides. With the growing season behind us, let’s review some of the do’s and don’ts concerning pesticides and their proper storage. First, let’s take a look at some general considerations that all homeowners who handle pesticides should be aware of. The most common mistake is failure to read and follow the pesticide label. Labels on most household chemical products contain important information on use and storage of the specific product. Most often the storage and disposal information is found toward the end of the pesticide label.

The first option for leftover pesticides is to use them. If there is not a use on your property, perhaps a neighbor has a need.

Another option is to dispose of the leftovers at a local household hazardous substance recall event. These events are sponsored by various organizations and agencies at various locations. Watch for such events through media channels such as the local newspaper, radio and television stations. Some of these events may be free of charge, while other organizations may charge according to the amount returned.

Many pesticides will be stored in various places until needed next year. This brings up several questions, the first of which concerns proper temperature requirements. Some pesticides require storage at temperatures above freezing to retain their shelf life, while others have no such requirement. The difference is based on chemical factors of the specific contents such as the solvents and inert ingredients used in the manufacturing process. Under the storage section of the label, the user may note statements such as: "do not allow to freeze," "low temperature may cause crystallization," "not sensitive to light or heat," and "extremely stable under normal conditions." There are many other important statements regarding the temperature and sometimes even light requirements concerning storage found in this section of the label.

Another question concerns the shelf life of a pesticide, and this, too, is also extremely variable. The following table shows the shelf life of a few of the commonly used lawn and garden pesticide active ingredients (assuming they have been stored properly):

Active ingredient Shelf life bensulide indefinite 2,4-D amine indefinite 2,4-D ester 2+ years dicamba at least 2 years glyphosate at least 2 years acephate 2+ years carbaryl several years malathion indefinite captan 2+ years

Generally, wettable powders and granules are not affected by low temperatures. Moisture can wreak havoc on these types of materials, however. Caking (tombstone formation) is caused by moisture and can lead to chemical changes that may reduce their effectiveness. Keeping these materials dry should be the primary concern.

Products formulated in water-soluble bags require special winter storage. They have a high affinity for moisture and become brittle when frozen. If handled while brittle, they can easily break open. Therefore these materials will need not only a dry storage area, but heat as well.

One of the most unfortunate — and avoidable — consequences of improperly stored garden chemicals is that a pesticide is consumed from a container other than its original and intended container. In a survey conducted in the mid-1990s, data from the American Association of Poison Control Centers indicated that of more than 22,000 cases of pesticide exposures reported, more than 7,000 involved children less than 6 years of age. It’s little doubt that many of these cases could have been avoided if more stringent measures were taken in storage of those pesticides. Not only pesticides, but other household materials, such as cleaning fluids and paint thinners need to be stored in their original containers. If it is necessary to transfer the contents to a new container, the original label should be transferred and attached as well. Any container that once held a household pesticide should be triple rinsed and disposed of in such a way that children and pets will not have access to it.

If there is any doubt, always consult the pesticide label; it is the final word regarding the use of that pesticide. There is more detailed information available at your local University of Missouri Extension Center. MU has a guide that will help you understand pesticide labels. Request MU publication G1911, Understanding the Pesticide Label. More specific information on temperature and storage effects can be found in MU publication IPM1012, Temperature Effects on Storage of Greenhouse, Ornamental and Turf Pesticides. Both guides are available through your local University of Missouri Extension Center or from Extension Publications at MU:
Phone: 1-800-292-0969
On the Web: http://muextension.missouri.edu/explore/

Fred Fishel, Extension Pest Management/Pesticide Training Coordinator, UMC (573) 884-6361