Those #@$% Leftover Pesticides

On a fairly regular basis, we receive questions concerning the options for leftover pesticides. For example, last week I received a question from a caller wanting to know if it was safe to store pesticides with foodstuffs in a root cellar. Based on that call and other similar requests, we need to provide some guidance on dos and don’ts concerning pesticides and their proper storage. First, let’s take a look at some general considerations which 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 will contain important information on use and storage of the specific product. Most often, the storage and disposal information will be found towards 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, as some are held at regular time intervals. 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 which concerns proper temperature requirements. Some pesticides will require storage at temperatures above freezing to retain their shelf life, while others do not need this 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 as you probably suspect, this is also extremely variable. The chart on this page shows the shelf life of a few of the commonly used household pesticide active ingredients (assuming they have been stored properly).

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 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 not only need a dry storage area, but heat as well.

About once each year, I hear of an unfortunate situation where a pesticide was consumed from a container other than its original and intended container. 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 a manner 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 Outreach and Extension Center. MU has a guide that will help you understand pesticide labels. Request MU Guide G1911, Understanding the Pesticide Label. More specific information on temperature and storage effects can be found in MU Guide IPM1012, Temperature Effects on Storage of Greenhouse, Ornamental and Turf Pesticides. Both guides are available through your local University Outreach and Extension Center or by calling 1-800-292-0968 or on-line at http://muextension.missouri.edu/xplor/.

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
acpehate	2+ years
carbaryl	several years
diazinon	5-7 years
malathion	indefinite
captan	2+ years

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