Ministry of Agriculture
Mixing & Loading Pesticides
- Before You Start
- Choosing a Mixing Site
- Mixing Procedures
- Closed-Handling Systems
- Managing Rinsate
- Compatibility - Tank Mixing Pesticides
The most dangerous work with pesticides is pouring and mixing. These activities pose the greatest risk to human safety because handlers are exposed to concentrated products. Mixing and loading organophosphorous and carbamate insecticides can present a serious safety hazard, particularly when they are formulated with the solvent xylene which promotes their absorption through the skin. The environment is also at risk because pesticide spills are most likely to occur at this stage. Reduce risks by following label directions and the safety guidelines listed below.
- Read the product label before mixing a pesticide. Follow the safety precautions on the label, and understand the instructions for mixing.
- Wear the correct protective clothing; this may include rubber boots, chemical-resistant aprons, coveralls and gloves, a face shield, a hat and possibly a respirator (see Personal Protective Equipment heading in this section).
- Check the spray equipment for cracked hoses or leaks. Make sure the filters, screens, and nozzles are clean.
- Have emergency wash facilities, first aid equipment and emergency phone numbers close at hand.
- Calculate how much pesticide you need for mixing. Make sure your application equipment is working and properly calibrated (see the Application Equipment section of this website).
- Choose a mixing and loading site away from people, livestock, pets, wells and water bodies.
- If a mixing site is unavoidably near a water body, ensure the area is graded to slope away from the water.
- Mixing and loading sites should be outdoors. If you must work indoors, make sure the area is well ventilated.
- Mix pesticides only in good light.
- Keep soap and an emergency water supply nearby.
- Mix pesticides in still or low wind conditions. Stand upwind of the pesticide.
- Begin by filling the spray tank 1/3 to 1/2 full with clean water. NEVER put the chemical in first and then top with water. Start the agitator and then add the required quantity of chemical. Continue agitating while filling the tank.
- Prevent overflow. Do not leave your tank unattended.
- Mix and weigh out pesticides on a sturdy level bench or table. It should be made of materials that will not absorb pesticides, or be covered with heavy plastic. Don't use the bench or table for any other purpose. Label all weigh scales, measuring cups, pre-mixing pails, and knives for opening pesticide packages "for pesticide use only." Return them to the locked storage area when they are not in use.
- Stand on a sturdy platform when you add the pesticide to the tank.
- Hold the container below eye level when measuring or adding pesticide into the spray tank to prevent splashing or spilling pesticide in your face or eyes.
|Sturdy table covered with plastic for weighing pesticides||
Do not tear open paper pesticide bags. Slit them open with a sharp knife.
- Measure accurately. Don't guess. Small errors in measuring can cause large errors in application rates. Mix only the amount you plan to use immediately.
- For best results, wettable powders should be premixed before being added to the spray tank. Make a slurry of wettable powder and water and then pour it into the spray tank.
- Always follow manufacturer's directions when mixing.
- Add adjuvants before pesticides, unless label instructions say differently.
- If you splash or spill a pesticide while mixing or loading, stop IMMEDIATELY. Remove contaminated clothing and wash thoroughly with soap and water. Obtain medical assistance if exposure could result in more than a mild irritation. Speed is essential when you or your clothing are contaminated. Clean up any pesticides spilled.
- Rinse pesticide containers as soon as they are empty. When residues dry they are difficult to remove. Triple rinse containers which held liquids and single rinse bags. See the table below for more information on triple rinsing containers.
- Rinse measuring cups and mixing equipment. Pour all rinse water into your sprayer.
- Replace container caps and close bags. Return them to the storage area.
- Wash your gloved hands before getting onto the tractor, as your hands and forearms will have received the most exposure.
|Hold the container below eye level when adding pesticide to the spray tank.||Making a wettable powder slurry|
Triple Rinsing Procedure
|Container Size||Rinse Solution Needed|
|20 litres or less|
|1/4 of the container volume|
|More than 20 litres||1/5 of the container volume|
|100 litres or more|
|Do not require triple rinsing|
return containers to the dealer
|Amount Of Active Ingredient Removed From a 20 Litre Container By Triple Rinsing|
|Rinse Step||Amount of Active Ingredient (a.i.) Remaining*|
|Drain||14.1875 grams a.i.|
|First Rinse||0.2183 grams a.i.|
|Second Rinse||0.0034 grams a.i.|
|Third Rinse||0.00005 grams a.i.|
|*After draining, a 20 litre (˜5 gal.) container is assumed to still contain 28 grams (1 oz.) of formulated pesticide. This would amount to 14.1875 grams of a.i. if the formulation contained 1.8 kilograms (4 lbs.) of a.i. per litre.|
- Gravity systems are sometimes called "punch and drain" systems. The unopened pesticide container is inserted into a chamber, which is then sealed. A punch cuts a large opening in the container, allowing all of the material to drain into the mixing tank. A water nozzle attached to the punch sprays the inside of the container to rinse it thoroughly. The rinse water also drains into the mixing tank. The rinsed container is then removed for disposal. A limitation of this system is that only full container quantities can be used.
- Suction systems use a pump to remove the pesticide through a probe inserted into the container. Some containers are equipped with built-in probes. The pesticide is transferred to the mixing tank by hose and pipe. When the container is empty, it and the transfer system are rinsed with water. The rinse water is added to the mixing tank.
- Back-siphonage. This is a reverse flow of water caused by a reduction in water pressure. If a hose used for adding water is immersed in the pesticide spray tank, back-siphonage may draw the pesticide concentrate back into the main supply line. Water downstream of the main supply line will then be contaminated. Back-siphonage can occur when there is a large draw on the main supply line such as for fire-fighting or due to a break in the supply line.
- Backpressure backflow. This is a reverse flow which occurs when systems such as mixing tanks are above the height of the water supply source. For example, a pump may supply water from a pond to a mixing tank on a truck. If the pump fails, backpressure could cause the pesticide mixture to flow through the supply line into the pond.
Prevent contaminating the water supply by leaving at least a 15 cm air gap between the end of the filler hose and the water in the spray tank at all times.
Backflow prevention devices
If an air gap is not possible, such as when the pesticide is injected into an irrigation system, a backflow prevention device must be used. These devices must be tested upon installation and on an annual basis. Examples of backflow prevention methods are shown below.
Atmospheric Vacuum Breaker: can prevent a reverse flow of concentrated pesticide into the hose and into the water supply system if pressure in the water system drops.
Backflow Preventer (with a vehicle): is required to prevent a reverse flow of pesticide into a water supply in the event a pump fails.
Backflow Preventer (in an Irrigation system): is required to prevent pesticide injected into a system from flowing back into the supply line rather than out through the sprinkler heads.
Minimize the amount of rinsate you produce, and manage or recycle rinsate on the farm.
- Use the minimum amount of water needed to effectively rinse containers or spray tanks. (See table above for recommended amounts.)
- Take precautions to avoid spills.
- Used a closed handling system where applicable.
- Add rinsate to the spray tank immediately after rinsing containers.
- Use rinsate as a diluent for future field tank mixes if safe to do so (label rates should not be exceeded).
- Label any containers with stored rinsate.
For tank-mixes of two or more chemicals, first check the product label for compatibility information. Incompatibility may be physical, causing clumping, sediments or separation of liquids. This may result in clogged sprayers or damaged equipment, as well as reduced effectiveness and injury to plants (phytotoxicity).
Add the first chemical at the 1/3 to 1/2 full stage and the second chemical at the 2/3 to 3/4 full stage. Mixing by this method will ensure that the chemical is completely mixed in the water. To keep the chemical completely mixed keep the agitator on until you are finished spraying.
Take precautions when trying new tank mixes. Test the mixture for physical compatibility using the "jar test" - Mix up a small amount of the pesticide(s) in the relative proportions that you plan to use them. Check that the products mix well and do not settle out rapidly upon standing. Test new mixtures on a small scale to determine whether the mixture may cause injury to the crop.