Montana State University

Watch winter storage temperatures of herbicide

August 23, 2005 -- By Fabian Menalled menalled@montana.edu MSU Extension Service Cropland Weed Specialist

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Tel: (406) 994-4571
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Farming is a year-round activity and as we finish harvesting this year's crops, we need to start thinking about how to store leftover or advanced purchased herbicides this winter.

Proper herbicide storage is essential to protect people, animals and the environment from accidental exposure. Proper storage also protects herbicides from cold temperatures that may degrade them and from temperature extremes that may generate excessive pressure within containers, causing them to break. In this article, I review some easy to follow guidelines to securely store herbicides during this coming winter. Although I concentrate on herbicides, most of the recommendations apply to other pesticides such as insecticides and fungicides.

Labels. Perhaps the most simple and appropriate recommendation for herbicide storage is to check the label. Herbicide labels have valuable information on storage needs. Carefully read labels and follow the instructions for proper over-winter storage.

Site Selection. If stored safely, herbicides pose no danger to humans, animals or the environment. Several issues should be considered when selecting a herbicide storage site. First, the storage should be in an area where flooding and fire are unlikely. Second, the site should be located far away from any water body or well so that runoff or leaching cannot contaminate surface or groundwater resources. If it is not possible to locate a storage facility far enough from wells and surface water, it is necessary to implement water-source-protection measures, such as runoff diversions or covered well heads. Finally, the storage area should be located downwind and downhill from sensitive areas such as houses, gardens and playgrounds.

Storage Building. Herbicides should be stored in a locked, dry and well ventilated building. The storage facility should be fire resistant with a curbed impermeable floor (such as concrete) to eliminate the risk of pesticide leaks or spills from spreading and leaching into the unprotected ground. Signs or labels should be posted on the outside of the building to identify the area as a pesticide storage area. These labels will give firefighters information about pesticides in case of a fire or spill.

Insecticides and fungicides could be stored in the same storage facility as herbicides, but they should be kept on separate areas or different shelves to prevent cross-contamination. Large drums or bags should be stored on pallets and off the floor. Dry products should be located above liquids to prevent wetting from spills. Check herbicide containers for cracks, tears or leaks that may occur during cold weather. Also make sure they are sealed tightly. Finally, it is a good idea to maintain, in a separate location, a list of the chemicals and amounts stored.

Over-winter herbicide storage. As a general rule, dry herbicide formulations and granules are not affected by cold or freezing temperatures. However, they need to be kept dry, because moisture can cause caking and breakdown of the container. Although liquid formulations vary greatly in their response to low temperatures, more often than not when a liquid herbicide freezes, the only risk is separation of the active ingredient from the solvents or emulsifiers, leading to crystallization or coagulation of the active ingredient. Some herbicides require being stored in cold-climate areas to minimize degradation.

The main concern when storing herbicides in cold conditions is that if the liquid expands upon freezing, the container holding the pesticide may crack or rupture. The simplest solution to this problem is to avoid excess pesticides that require winter storage. If over-winter storage is necessary, the following information, adapted from the 2005 North Dakota Weed Control Guide, gives the minimum storage temperature to avoid risk of reduced herbicide activity.

No storage temperature restriction: Metolachlor products, EPTC, Surpass, Achieve, Maverick. Most dry formulated herbicides in DF or WDG formulations.

Do not store below 40 degrees Fahrenheit:
Assert, Avenge, Campaign, Command, Discover, Extreme, LI-700, Nortron, Prowl, Pursuit Plus, Sonalan, trifluralin.

Do not store below 32 degrees Fahrenheit
Agri-Dex, Basagran, Far-Go EC, Flexstar, Goal, paraquat, Grazone P D, Hyvar, Kerb, Liberty/ATZ, Lorox DF, Poast, Pramitol, Progress, Puma, Pursuit, Quest, Raptor, Redeem, Reflex, Reglone, Stinger, Thistrol, Ultra Blazer, Velpar.

Do not store below 20 degrees F Fahrenheit
Fusilade DX, Plateau, Ro-Neet, Weedar 64.

Do not store below 16 degrees Fahrenheit:
Camix and Lumax.

Do not store below 10 degrees Fahrenheit:
Amitrole T, Arsenal, Curtail/M, Crossbow, Dakota, Fusion, glyphosate, Rodeo, Roundup.

Do not store below 3 degrees Fahrenheit:
Atrazine 4L, Low Vol ester, Bronate Advanced, bromoxynil, bromoxynil Atrazine, Shotgun.

When the winter is over, herbicides should always be checked before they are used. Liquid products that have become separated, crystallized or coagulated should be placed in a warm area (about 70 degrees F) for several days, during which the containers should be inverted or shaken periodically. Usually, the warm temperatures and agitation are enough to redissolve the crystals into the solvent. If the solution does not redissolve, it probably should not be used.

Disclosure. Common chemical and trade names are used in this publication for clarity by the reader. Inclusion of a common chemical or trade name does not imply endorsement of that particular product or brand of herbicide and exclusion does not imply non-approval.

Contact: Fabian Menalled (406) 994-4783 menalled@montana.edu