Winterizing Spray Equipment and Cold Storage of Pesticides

Cecil Tharp, MSU Pesticide Education Specialist


Applicators should take time to prepare spray equipment and pesticide supplies prior to long term storage during the winter months. Avoiding servicing spray equipment for winter storage can be a costly mistake. This is accomplished by cleaning sprayers thoroughly, draining pesticide residual from tank, and inspecting sprayer components.

Cleaning Sprayers

The outside of a sprayer should be washed, while also rinsing spray tanks. Spray tanks can be rinsed by circulating water through the spray system. Add water up to 10% of spray tank capacity and spraying on a labeled site. Many pesticide product labels will recommend adding select cleaning agents to spray tanks to aid in removing water and oil soluble pesticides (Table 1). Tank cleaning agents work in a variety of ways including:

  1. Addition of ammonia to raise pH of rinsate solution increases water solubility,
  2. Addition of chlorine bleach increases the breakdown of many pesticide products into inactive compounds,
  3. Addition of fuel oil or kerosene removes oil soluble pesticides including esters and emulsified concentrates. Nozzles, screens, and strainers should be removed and cleaned separately in a bucket containing water and the recommended cleaning agent once the tanks have been cleaned.

Bleach should never be mixed with ammonia as this creates a deadly chlorine gas.

Fuel or kerosene should be followed by a detergent rinse to remove oily residue. Cleaning agents should be washed through entire spray system prior to rinsing with clean water. It is critical that all ‘rinsate’ be sprayed upon a site written on the pesticide product label or collected into containers and treated as pesticide waste. Always follow the pesticide product label cleaning instructions if available.

Final Inspection and Preparation for Storage

Upon final rinse inspect nozzles, hose clamps, screens, valves, hoses and tank for wear or damage. Pay particular attention to discoloration of poly tanks from sun damage, which significantly weakens tank integrity. For larger spray rigs this is the time to grease fittings, inspect engine belts, and clean / remove batteries. To protect sprayer pumps and lines from corrosion and freezing damage over the winter months circulate antifreeze through entire sprayer. A 50/50 mixture of antifreeze and water should be pumped through system for at least 5 minutes.

Table 1. Cleaning Solutions for Pesticides.*

Pesticide Used

Step 1 - Mix Solution
(per 25 gallons)

Step 2 - Agitate

Step 3 - Wait and Flush

Hormone Herbicides

(2,4-D salt, amine, brush killers, MCPA, dicamba)

  1. 1 qt. household ammonia, or
  2. 1 lb. washing soda (sal soda), or
  3. 2 lb. trisodium phosphate, or
  4. ½ lb. fine activated charcoal and ½ cup detergent

*follow the same letter through all steps

  1. Agitate solution for 15 minutes.
  2. Agitate solution for 15 minutes.
  3. Agitate solution for 15 minutes.
  4. Agitate sprayer for 2 minutes.
  1. Let stand overnight. Flush with clean water.
  2. Let stand for 2 hours Flush with clean water.
  3. Let stand for 2 hours Flush with clean water.
  4. Let stand for 10 min. Flush with clean water.

Hormone Herbicides ester form

(2,4-D, brush killers, MCPA)

1 lb. washing soda (sal soda) + 1 gal kerosene + ¼ lb detergent.
Rinse inside of tank and flush small amount through system.
Let stand for 2 hours. Flush and rinse.

Amino Acid Inhibitors

(SU’s including primisulfuron, prosulfuron, and halosulfuron)

2% household ammonia then circulate for 15 minutes and flush.
1% household ammonia, circulate for 15 mins then flush.
Rinse tank for minimum of 5 minutes using clean water.
Organophosphate or carbamate insecticides
1 qt household ammonia + ¼ lb detergent.
Flush a small amount through system.
Rinse with clean water.
Other herbicides and insecticides
¼ lb detergent.
Flush a small amount through system.
Rinse with clean water.

 *Applicators should always read and follow any pesticide product label cleaning instructions.


With the antifreeze mixture still in the system remove some components:

  • Remove pressure gauges and check valves. Store in marked container at room temperature over the winter to avoid damage from freezing temperatures. Plug assemblies.
  • Nozzles and screens should be removed and placed into a marked container filled with lightweight oil (kerosene or diesel fuel). Correctly plug these assemblies as well.

By capping assemblies, remaining antifreeze will ensure that lines don’t freeze and crack. Antifreeze should remain in sprayer through winter months to avoid air moisture from corroding internal components of sprayer. Sprayer should be ready for storage in a sheltered location away from liquid and dry fertilizers which will corrode paint and hardware. 

Long Term Storage of Pesticide Products

Dry formulations (ex. granular and wettable powders) are not generally impacted by freezing but should be stored in a dry location. Liquid pesticides may freeze and result in separation of the active ingredients from carriers, which could reduce effectiveness of pesticide product. This reaction may include coagulation or crystallization which may cause further plugging of spray lines. Some frozen pesticide products often retain effectiveness if applicators follow steps when thawing and re-dissolving the suspension.

Pesticide products have different freezing temperatures due to the presence of hydrocarbon solvents in many formulations. Hydrocarbon solvents actually reduce the freezing point below 32 degrees F. Pesticide product labels often explain a pesticides minimum storage temperature, in addition to whether:

  1. Freezing poses a problem,
  2. Active ingredients separate from carriers if frozen,
  3. Effectiveness of a pesticide is reduced if frozen, and
  4. The active ingredients and inert ingredients go back into suspension.

Applicators should always be familiar with storage directions on their pesticide product label. For more information consult the chemical manufacturer or read the MontGuide titled ‘Cold Weather Storage and Handling of Pesticides’ or Maintenance, Cleaning and Storage of Ground sprayers at by selecting ‘Reference Material’. These can be downloaded and printed free of charge.

For Further Information

For a more detailed guide to winterizing spray equipment see the Purdue Extension publication titled Preparing Spray Equipment for Winter Storage and Spring Startup. Contact the MSU Pesticide Education Program if readers have any further questions (Cecil Tharp, 406-994-5067, [email protected]).

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