Plant Pathology Infobytes

April 16, 1997
Leftover Fungicides - Are They Safe For Use This Season?

Each spring, home vegetable gardeners and orchardists have questions concerning the use of pesticides carried over from the previous season. "Are these products still okay to use or have they lost their effectiveness?"

While the following guidelines relate primarily to fungicides, they are also applicable to most other carryover pesticides from 1996 or an earlier season.

Many leftover fungicides may be used the second year provided they have been stored properly in an area where they haven't been exposed to freezing temperatures during the winter or high temperatures during the summer.

Homeowners should carefully examine any leftover containers for leaks, cracks, tears, worn areas, seal failures, and bulges. Bulges on a metal container may be a sign of gas development which can make handling or opening the container hazardous.

The presence of a strong odor indicates an improperly sealed container, a leak, or possibly a spill. When there are doubts concerning effectiveness, age, and condition of a fungicide after long term storage, test for deterioration.

Signs of deterioration observed with various formulations of pesticide include the following:

 

  • Wettable powders - excess lumping occurs and the powder will not suspend in water.
  • Emulsifiable concentrates - milky coloration fails to occur when water is added; sometimes a "sludge" occurs which may indicate separation of pesticide components.
  • Flowable type fungicides - will not properly mix and it is almost impossible to get the sediment in the bottom of the mixing container back into suspension.

If any of these signs are detected as you prepare fungicides, or other pesticide mixes for pest control in vegetable gardens, orchards, or for use in the landscape, the best advice is "don't take a chance." Not only is it likely that such fungicides are not going to be effective in controlling plant diseases, there's a chance that spray mixes prepared from such products will cause severe plant injury.

When fungicides and other pesticides are determined to be unusable, they should be properly disposed of according to local, state, and federal regulations.

For information on pesticide disposal, please feel free to check with us at the County Extension Office.


Written by the late Dr. Frank Killebrew

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