While buying in bulk might be good for dry goods and groceries, today the pesticide recommendation is to only purchase in the volume you expect to use in a single growing season, with an exception and there will always be one of those.
First, a bit of vocabulary is needed to understand the various product types that gardeners routinely buy and use in the home landscape and gardens:
Liquids – the active ingredients dissolve completely in water and no agitation during application is needed forming a true solution.
Emulsifiable concentrate – the active ingredient will dissolve in oil, but not in water and is later mixed with water for application.
Wettable Powders – a dry powder that does not dissolve, but held in suspension with agitation during application.
Dusts – active ingredient is placed on finely ground particles, applied by shaking the container or in a special applicator using air.
Gardeners should not attempt to keep mixed diluted sprays, but rather use them up on the target plants at the end of the growing season. The quality of the water from the spigot on the house can degrade the active ingredient and the spray next season will be ineffective in managing the target pest.
Liquids and emulsifiable concentrates must be kept above freezing to prevent separation and potentially bursting the container. Freezing temperatures will not harm dusts and wettable powders. In general, the best storage conditions will be to keep the unused concentrates in a cool and dry location. Dry for the wettable powders and dusts so they do not absorb moisture and clump or cake up. If enough moisture is present, the active ingredient or other additives may cause the product to be ineffective.
Storage locations could be a garage that stays above freezing or in the basement away from any heat sources. In terms of safety, a lockable cabinet is preferred over a shelf. If it is a shelf, make it out of reach of children and pets.
The exception I noted at the top of this column relates to how long we can keep a product in concentrated form. Wettable powders often used in a home orchard with more than just a few fruit trees can be kept several seasons if stored properly during the growing season and winter storage. All the rest should be used in a single season if possible. This includes insecticides, fungicides, herbicides and any other kind of pesticides.
By following good integrated pest management and good agricultural (gardening) practices, you will keep the need to treat with a pesticide down to a minimum, reducing what will need to be stored and in the big picture, gardeners become a better steward of the land.Richard Hentschel is a Horticulture Extension Educator with University of Illinois Extension, serving DuPage, Kane and Kendall counties. Stay tuned to more garden and yard updates with "Down the Garden Path" at go.illinois.edu/downthegardenpath and the "Green Side Up" podcast at web.extension.illinois.edu/podcasts/greensideup