When storing leftover or advance purcbased herbicides over the winter, growers need to ensure that quality is preserved and spills or contamination avoided, according to Dallas Peterson, Extension weed control specialist at North Dakota State University.

The best type of storage environment will depend on the formulation and the chemical to be stored. Always check the herbicide label for handling and storage instructions to avoid mistakes and accidents, Peterson says. All types of storage facilities should be well ventilated, posted with signs, and locked.

Before storing, check herbicide containers for cracks, tears, or leaks, and make sure they are sealed tightly. Herbicides should also be isolated from seed, fertilizer, feed, and clothing because accidental spills or leaks during storage could contaminate the other materials and leave them unusable.

While dry herbicide formulations such as wettable powders, dry fiowables, and granules are not affected by cold or freezing temperatures, they need to be kept dry because moisture can cause caking and breakdown of the materials. When dry and liquid products are stored in the same area, the dry materials should be stored above the liquid materials to prevent contamination if the liquid container should leak, says Peterson.

Liquid formulations vary greatly in their response to low temperatures, Peterson says. Freezing can cause the container to rupture or can inactivate the herbicide. Low temperatures often cause the emulsifiers in some formulations to separate out, leading to crystallization or coagulation of the active ingredient, he adds.

Herbicides stored over the winter should always be checked in the spring before they are used. Liquid products that have become separated, crystallized, or coagulated should be placed in a warm area (approximately 70oF) for several days and inverted or shaken periodically during that time. The warm temperatures and agitation are often enough to redissolve the crystals into the solvent. If the solution does not redissolve, it probably should not be used, Peterson says.