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Is that pesticide still good?

Farmers often pre-buy pesticides and bulk buying is on the rise. The reasons for doing so makes sense — some want put-off taxes by purchasing before their year-end; others purchase early to take advantage of sales and promotions from chem companies. There can also be money saved by buying pallets, large totes or even bulk deliveries of a pesticide, even when you won’t use all the product in one year. The issue with pre-buying product is that there is a cost to storage and a shelf life for many product.

Fortunately, most pesticides are relatively stable products and nearly all pesticides will have a shelf life of at least two years when or if stored properly. Glyphosate is an example of a very stable herbicide. Although glyphosate freezes, after it thaws it goes back into solution. For example, the MSDS for Polarisbrand glyphosate, the brand used in the Racketeer bulk system, states: “Product is stable under normal conditions of storage and handling for at least five years.”

However, this is not to say glyphosate has no storage issues. Glyphosate cannot be stored in galvanized steel or unlined steel tanks. Glyphosate will react with the metal and produce highly explosive hydrogen gas. Even though glyphosate has a long shelf life, and is not affected by freezing, there are still storage concerns that a farmer needs to be aware of. Storage restrictions, if any, will be listed on the label of a pesticide.


When storing any pesticide, the most important factor in determining its shelf life is temperature. The ideal temperature range for pesticide storage is between 5 C and 40 C. Temperatures above or below this normal range can reduce the effectiveness of some pesticides.

The fact sheet, Temperature Effects on Storage of Agricultural Pesticides put out by the University of Missouri identifies the effect temperature has on a pesticide. The fact sheet states: “Freezing of liquid pesticides can result in separation of the active ingredients from the solvents or emulsifiers, or inactivation of emulsifiers, which may lead to crystallization or coagulation of the pesticide.”

On the other hand, high temperatures can cause some pesticides to degrade through vaporization.

Signs a pesticide may have deteriorated

Shake it up

Checking the label of the pesticide is the best way to determine if there are any temperature restrictions for storage. All pesticide labels have a section detailing storage. For example, the Liberty herbicide label states (in part):

Section 5: Storage

  1. Cannot be stored below freezing.
  2. If stored for one year or longer, shake well before using.
  3. Store the tightly closed container away from feeds, seeds, fertilizers, plants and foodstuffs.
  4. Keep in original container during storage.
  5. To prevent contamination; store this product away from food or feed.

Since Liberty is available in large totes, some farmers may have carryover between years. If so, this product must be kept in heated storage. Farmers must also be aware “shaking well” can be a problem for a partially filled or full tote. While buying a tote may seem to be a good investment, unless you can use that amount in the growing season, it may prove to be a real problem to handle and store in the long-term.

Pesticide storage regulations

Besides worrying about a loss of pesticide efficacy, farmers must also store pesticides safely. Pesticide storage is regulated provincially so a grower needs to know the regulations in their province with regard to on-farm storage of pesticides.

In Alberta, all federally approved, commercial, agricultural pesticides are subject to the Environmental Protection and Enhancement Act. Jock McIntosh, Pesticide Policy Advisor, Alberta Environment says the most important regulation Alberta farmers must follow when storing pesticides on farm is: Pesticide Sales, Handling, Use and Application Regulation 24/97, Section 23 “Storage of Pesticides,” 2) No person shall store food or personal use items in a storage facility where a pesticide listed in Schedule 1 or 2 is stored. McIntosh points out that Schedule 1 and 2 includes all commercial agricultural pesticides.

Farmers who are custom applying pesticides, as well as retail sellers of pesticides are subject to further storage regulations. These additional restrictions found in the Act are also recommended practices for farmers in the Alberta Environmental Farm Plan (

If you are going to store pesticides on your farm, know the regulations in your province for farm storage of pesticides and read the pesticide label to find out if there are any specific storage requirements for that pesticide.


The Alberta Agriculture website provides a complete listing of the storage requirements for all herbicides registered for use on the Prairies. From the homepage, click on the “Decision Making Tools” tab, and click on “Herbicide Selector.” On the right hand side of the page, you’ll find a list of reference links including “Mixing Instructions and Storage.” Opening this link will provide an alphabetical listing of all herbicides and the detailed mixing and storage instructions as found on the label. Pesticides not listed above have no specific storage temperatures listed on the label. However, many of these other products’ labels warn that if freezing occurs the pesticide has to be warmed and shaken well before being used.

Growers also need to be aware that extreme temperatures can physically damage the pesticide container. Plastic, metal and glass containers can break open under extreme temperatures. While dry formulations tend not to be affected by temperature, the soluble bags they are stored in can become brittle and break under low temperature storage.

High humidity is a deterioration factor when storing wettable powders and granule formulations of pesticides. It is important to store these pesticides in cool, dry environments to not only prevent caking but possible reduction in effectiveness of these types of products.



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