February 2012 Newsletter (vol.4)   >>   Shelf Life

It is that time of year again to begin thinking about what chemicals you will need for the growing season. You want to make sure you have what you need in time to manage the infestations before they get out of control. You may have some pesticides left over from last year’s growing season that you didn’t use, but will they still be effective? What is the shelf life of pesticides and how do you know when a pesticide is no longer effective?


First, it is essential to review some general guidelines for storing chemicals, whether it is insecticides, herbicides, fungicides, miticides, or growth regulators.


  1. Chemicals should always be stored away from the general public, especially children and pets. Store them in an “employee only” designated location labeled as chemicals or pesticides. See Hummert’s worker protection signs and our pesticide storage cabinets.
  2. Keep them in a well ventilated locked cabinet or room that stays cool and dry. Temperatures should stay above 40 degrees but never exceed 100 degrees.
  3. Always try to purchase chemicals in a small amount to be used in one season. This limits the questions of whether a chemical is good or not, or where to store it until next year. Generally manufacturers recommend storing chemicals no longer than 2 years.
  4. Write the purchase date on the container, and use a first in-first out inventory method.
  5. Keep the chemicals in the original containers. Be sure the caps are securely tightened.


How long a chemical remains effective depends upon the formulation, length of storage, and conditions during storage. Every chemical label has a section of the label dedicated to storage instructions which should be followed. If a chemical has been stored for an extended period of time, you will see indications that it has started to breakdown and is no longer good. See below chart for signs of breakdown.


Formulation Signs of Breakdown
Oil Sprays Sludge forms, solution separates
Emulsifiable Concentrates - EC Addition of water does not produce a milky solution
Wettable Powders - WP Clumping, powder will not mix with water
Dusts & Granules Excessive Clumping
Aerosols Generally effective until nozzle clogs or propellant is dissipated


Pesticide Formulations
One or more active ingredient (a.i.) in solvent; lower a.i. ready-to-use or smoke or fogger; easy-to-use.
F, L – Flowables
Insoluable solids, finely ground a.i. mixed with liquid and inerts.
Advantages: Seldom clog nozzles; easy-to-handle and apply.
Disadvantages: Requires agitation; may leave residue.
C, LC – Concentrate or Liquid Concentrate
Advantages: No agitation necessary.
Disadvantages: Must be further diluted in water or petrol; limited number of these.
G – Granules
Advantages: Ready-to-use, no mixing, low drift hazard.
Disadvantages: Does not adhere to leaf surface, may need irrigation to activate.
D – Dusts
Ready-to-use low a.i. %; talc, chalk, clay, nut hulls, etc.
RTU – Ready-to-use
Advantages: No further dilution necessary.
Disadvantages: Petrol-based solvents can pit surfaces.
DF, WDG – Dry Flowables or Water-Dispersed Granule
Similar to wettable powders but prepared as a granule.Advantages: Easily measured and inhalation risk reduced. Disadvantages: requires constant agitation
SP, WSP – Water-Soluble Powders
Finely ground powders that dissolve in water to form a solution.
E, EC – Emulsifiable Concentrate
Advantages: Versatile; easy-to-handle; little agitation required; non-abrasive; won’t plug screens and nozzles.Disadvantages: High concentration makes it easy to overtreat; maybe phytotoxic; easily absorbed through skin; may cause sprayer parts to deteriorate; may pit some surfaces
WP – Wettable Powder
Dry and finely ground formulations that need to be mixed with water; they do not dissolve in water. Advantages:Less likely to be phytotoxic; not as easily absorbed into the body. Disadvantages: Settles out quickly and requires agitation; hard to mix in alkaline and hard water; often clogs nozzles and screens.
EW – Oil in Water Emulsion
A stable emulsion of a.i. in an aqueous phase that needs to be diluted in water; a.i. liquid forms a dispersed-oil phase; after storage it may be necessary to shake or stir.



According to a study done by Cornell University below are the estimated shelf lives for various pesticides.

Pesticides Shelf Life (years) Comments
Sevin, WP Several Flowables will settle
Diazinon 5-7  
Malathion, WP Indefinite Decomposes under high temperature
Captan, WP 3  
Thiram, WP 4 Keep dry, below 100 degrees
Dacthal, WP At least 2  
Roundup, liquid At least 2 Stable below 140 degrees, do not freeze
Surflan, WP 3  
Treflan, G 3 Loss 15-20% activity when stored at 100 degrees


"Shelf Life of Pesticides". Cornell University Cooperative Extension. <http://psep.cce.cornell.edu/facts-slides-self/facts/gen-peapp-shelf-life.aspx>.