7.9 Solutions for Safer Spraying
Reducing the risk of pesticide exposure through engineering controls34204
7.9.1 Why use Engineering Controls?
Because handling and applying pesticides is risky business, keeping pesticide exposure to a minimum should be a chief concern of any pesticide applicator. To reduce the risks associated with handling and applying pesticides, devices known as engineering controls can be used that help to reduce or practically eliminate exposure to toxic chemicals. This fact sheet describes various engineering controls that can help reduce applicator exposure to pesticides in five areas of potential contamination.34205
7.9.2 Loading the Sprayer
Closed Transfer Systems - Closed transfer systems allow concentrated pesticide to be moved from the original shipping container to the sprayer mix tank with minimal or no applicator contact. Many systems provide a method to measure the concentrated pesticide. Some systems also include a container rinsing system. Currently available closed transfer systems use a probe inserted into the pesticide container, a connector on the container that mates to a similar connector on the application equipment, or a vacuum-type (venturi) system that uses flowing water to transfer the chemical from the container.
Induction Bowls - Induction bowls are metal, plastic or fiberglass hoppers attached to the side of the sprayer or the nurse tank that allow pesticides to be added to the mix tank without the applicator climbing onto the spray rig. Pesticides are poured into the bowl and water is added to flush out the bowl and carry the pesticide to the spray tank. Often a rinse nozzle is mounted inside the bowl for rinsing out empty pesticide containers. Typically induction bowls are raised out of the way during spraying and lowered to about 3 feet aboveground when the sprayer is being loaded.
Direct Pesticide Injection System - Direct pesticide injection systems allow pesticides to be mixed directly with water in the sprayer plumbing system rather than in the main spray tank. The pesticide is pumped from its container and mixed with the water either in a manifold or at the main water pump. Only clean water is held in the main tank of the sprayer. An electronic controller and up to four pumps adjust the amount of concentrated pesticide that is injected into the water stream, allowing for variable application rates.
Container Rinse System - Container rinse systems consist of a rinse nozzle and a catch bowl that traps the container washings (rinsate). The empty container is placed over the rinse nozzle and a jet of water cleans the inside of the container. The rinsate caught in the bowl is pumped into the spray tank to be used along with the spray mixture. Often rinse nozzles are installed in chemical induction bowls. Most closed transfer systems also provide a way of rinsing containers and piping the rinse water into the spray tank.34206
7.9.3 Reducing Contamination at the Boom
Boom Folding/Extending - Manually folding booms can be a major source of operator contamination because the boom can be covered with pesticide from drift or dripping nozzles. Consider the use of hydraulic or mechanical folding methods.
Diaphragm Check Valves - Typically, when a sprayer is shut off and as the system pressure drops, any liquid remaining in the boom piping drips from the nozzles, possibly dripping onto the boom or even the operator. Diaphragm check valves installed at each nozzle prevent this by using a spring-loaded rubber diaphragm to close off the flow of liquid once the system pressure drops below about 10 pounds per square inch. When the sprayer is switched on and system pressure builds up, the valve opens and allows the liquid to flow through the nozzles.
Multiple Nozzle Bodies - Contamination can occur when operators change or unclog nozzles during an application. Multiple nozzle bodies (or turret nozzles) allow operators to switch between nozzles with a turn of the nozzle body rather than having to unscrew or undo a threaded or a bayonet fitting.
Hand Wash Water Supply - Providing adequate wash water is essential (and often required). A simple container with a hand-operated valve can be mounted on the side of the sprayer to provide clean water for hand washing and personal hygiene.34207
7.9.4 Drift and Contaminated Clothing in Cabs
Cab Filtration Using Carbon Filters - Carbon filtration systems are used to remove pesticide odor and pesticide-laden mist from fresh air used in a tractor or self-propelled sprayer cab. Carbon filtration systems are often a standard feature on self-propelled sprayers. Now many factory installed tractor cabs offer optional filtration systems. In 1998, the American Society of Agricultural Engineers (ASAE) adopted testing standards for operator cabs used in pesticide application. Cabs certified under this standard meet the requirements for enclosed cabs contained in the Worker Protection Standard.
Protective Clothing Lockers - To prevent contamination of the tractor or sprayer cab interior, protective clothing should be removed before entering the cab. A few sprayer companies offer a simple compartment (or locker) mounted to the side or front of the sprayer where protective clothing can be stored. Alternatively a locker can be fitted to the mixer wagon.34208
Figure 7.9.1. Areas of potential pesticide exposure risk and engineering controls to reduce exposure.
7.9.5 Controlling Drift
Low-Drift Nozzles - Low-drift nozzles create larger-size droplets than conventional nozzles. The larger droplet sizes are less prone to drift, reducing environmental and operator contamination.
Air Induction (Twin Fluid) Nozzles - These nozzles allow air to mix with the spray liquid, creating large, air-filled droplets that have virtually no fine, drift-prone droplets. The droplets explode when they contact their target and offer similar coverage to droplets from conventional, finer-spray nozzles 34210
7.9.6 Cleaning the Sprayer
Tank Rinse Systems - Tank rinse systems consist of a clean water supply tank mounted to the sprayer and one or more rotating discs or nozzles mounted inside the main sprayer tank. Water is pumped from the clean water tank to the rinse nozzles, which spray water around the inside of the spray tank. These systems are designed for in-field rinsing of the sprayer so that the tank washings can be applied to the field at label rates.
Sprayers must be thoroughly cleaned inside and out after use. Ideally, a sprayer should be cleaned at the end of each day and especially before switching to a different pesticide. Pesticide residues left on the outside of the sprayer can cause operator contamination. Residues on the inside of the tank or left over pesticides trapped inside the sprayer plumbing system can contaminate the operator and possibly lead to crop damage. Growers should be concerned about this, especially if they are using one sprayer to apply different chemicals to different crops. In some cases, only a small amount of a pesticide remaining in the sprayer can cause significant crop damage or lead to an unacceptable residues on a crop. Crop contamination can even occur several months after a sprayer has not been properly cleaned. Where an airblast sprayer is used to spray different fruit crops, residue left in the tank can cross contaminate another fruit crop resulting in rejection by the processor. Sprayers can also retain tremendous amounts of pesticide solution. Depending on the size and design of the sprayer, there can be nearly 6 gallons of solution left in an airblast sprayer's plumbing. As illustrated in Table 7.9.1, research conducted on boom sprayers has shown that, depending on the spray tank size, the total chemical solution retained in the sprayer ranged from just under 3 gallons to over 12 gallons. The parts that retained the most chemical solutionare the chemical induction bowl, the booms, the tank and the pump and its related piping.34211
Table 7.9.1. Quantity and Location of Chemical Remnants in Crop Sprayers (in gallons)
159 Gallons- 39 foot boom
212 Gallons - 39 foot boom
396 Gallons - 59 foot boom
Pump and associated piping
Filter relief valve
Chemical induction bowl
Total without boom
Total with booms
Adapted from "Quantity and Location of Chemical Remnants within a Range of Field Crop Sprayers by S.E. Cooper. Available: www.hardiinternational.com/Agronomy/Education_Material/pdf/08a.pdf
Tests have shown that triple rinsing the spray tank is better than using just one single rinse. For example, using 100 gallons of clean water in one single rinse to clean a 100-gallon sprayer tank reduced the concentration of the original spray solution from 100% to 5% both in the tank and at the nozzle. If triple rinsing was performed using 33 gallons of clean water per rinse, a concentration of 0.2% to 0.5% was gained. The aim is for maximum dilution with minimal use of water. Table7.9.2 illustrates how triple rinsing reduces the pesticide concentration at the nozzle and the tank drain. 34212
Table 7.9.2. Concentration of Pesticide in Rinse Water
Source: Nilsson, E., Hagenwall H. og Jorgensen L.
Before rinsing a sprayer, read the sprayer manufacturer's instructions for specific guidance on the best methods for cleaning your equipment. Also consult the pesticide label for any special cleaning instructions. When cleaning spray equipment, you should use the protective clothing listed on the pesticide label. Sprayer cleaning should be done so that rinse water does not enter any waterway, field drainage system, or well. Ideally, sprayer rinsate should be applied to a labeled crop. If rinsing needs to be done at the mixing/ loading site, it must be done on an impervious surface. All contaminated rinse water must be trapped and either used to mix another load of the same pesticide at the label recommended rates or disposed of at an approved pesticide waste handling facility.
Reducing Cleaning Problems
The need for cleaning can be reduced by good planning and equipment maintenance. The following are suggestions to help reduce cleaning needs:
- Carefully plan how much pesticide to mix so that all mixed pesticides are used up when you are finished with the field.
- Be sure that the sprayer is clean before you use it.
- Make sure all parts of the sprayer are in good condition. Corroded, cavitated or pitted surfaces are prime areas for pesticide residue to hide. Replace any worn parts.
- Mix the chemicals in the correct order. Some chemicals, when mixed in the wrong order, can actually become more difficult to remove from the equipment. Consult the pesticide label for the proper mixing order.
- Follow any label instructions for cleaning spray equipment.
- Be sure that cleaning solutions contact ALL equipment surfaces.
- Remove and clean filters, strainers and nozzle screens separately from the rest of the sprayer.
Several sprayer cleansers are commercially available. These cleansers should be selected based on the pesticide formulation used. Specific recommendations can be found on the pesticide label, by contacting the pesticide manufacturer or through the label or manufacturer of the cleaning agent you wish to use. Some available cleansers are listed in Table 7.9.3. Household detergents, such as laundry soaps and household ammonia, can also be used, but they may not adequately deactivate and solubilize the pesticides for effective cleaning. Chlorine bleach solutions should not be used. Cleaning agents can be used to wash both the inside and outside of the sprayer. When using commercial cleansers, follow the product's instructions for the best results.34213
Table 7.9.3. Commercially Available Sprayer Cleansers
P.O. Box 64089
St. Paul, MN 55164-0089
Phone: (651) 451-5151
Helena Chemical Company
225 Schilling Blvd.
Collierville, TN 38017
All Clear Tank Decontaminator
Loveland Industries, Inc.
PO Box 1289
Greeley, CO 80632
Email: webmaster@ lovelandindustries.com
Ag Chem Tank Cleaner
Ag Chem Equipment Co.
202 Industrial Park
Jackson, MN 56143
Tank Rinse Systems (Low-Volume Tank Rinsing)
Tank rinse systems consist of a clean water supply tank mounted to the sprayer and one or more rotating discs or nozzles mounted inside the main sprayer tank. Water is pumped from the clean water tank to the rinse nozzles where the water is sprayed around the inside of the spray tank. These systems are designed for in-field rinsing of the sprayer so that the tank washings can be applied to the field and reduce the amount of time spent traveling.
A tank rinse system can be purchased as an option on some sprayers or as an add-on kit. Rinse systems can also be made from readily available parts and installed on the sprayer. A sample rinse system layout is shown on the next page. A typical rinse system uses 360-degree tank wash nozzles mounted in the top of the tank. These nozzles are available in flow rates of 10 gallons of water per minute at 20 psi up to 20 GPM at 50 psi. If a spray tank has baffles, at least one rinse nozzle per compartment should be provided. In any case, a sufficient number of rinse nozzles should be installed to provide enough rinse water to contact the entire tank interior.
A clean water tank can be plumbed into the sprayer plumbing system to provide the clean rinse water. This tank should be permanently marked "Clean Water Only" so that only clean water is placed in the tank, reducing the chance for contamination of the rinse system. The tank should be mounted above the pump in order to aid in priming the pump. Ideally, the tank should be mounted on the sprayer.
When using tank rinse systems, you may want to check the pesticide label or with the chemical manufacturer to be sure that low-volume rinsing is suitable for the products you're using. Also, during the rinse process, be sure to open and close the pressure valve and other control valves on the sprayer to ensure that any chemical that may be trapped in the valve is rinsed out, further reducing the chance for contamination of future pesticide mixes. To obtain the best results, practice using the rinse system by placing spray marker dye or food coloring in the spray tank. Using the rinse system, run three rinse cycles, making sure the water discharged from the nozzles is completely clear by the end of the third rinse.
Cleaning the Sprayer
The pesticide applicator should try to keep the volume of tank wash water produced to a minimum. Ideally a tank rinse system should be used.
Reminder: Before cleaning application equipment, remember to wear the protective clothing listed on the pesticide label.
- Be sure that all mixed pesticides have been used up from the sprayer or removed and disposed of properly.
- Flush sprayer with clean water, making sure to wash all inside surfaces of the tank, including the underside of the lid. Use of a tank rinse system is preferred so that rinsing can be done in the field where the rinse water can be applied to the crop. If a tank rinse system is not available, fill the spray tank about half full with clean water and flush the system for at least 5 minutes using both agitation and spraying. Be sure to open and close any control valves during the rinse process. The rinsate should be applied to the crop at labeled rates. Repeat this procedure two more times.
- Hose down the outside of the sprayer making sure to reach all parts, scrubbing if necessary.
- Remove suction, main and in-line filter elements and wash them thoroughly in clean water using a soft bristle brush. Put the filters back on the sprayer when clean.
- Remove the nozzles, nozzle screens and nozzle bar end caps (if used) and wash them thoroughly in clean water with the appropriate cleanser and rinse. Remember to use a soft bristle brush, such as an old toothbrush, when cleaning nozzle parts.
- Partly fill the sprayer with clean water and run the sprayer to flush out all parts.
- Reinstall nozzles and nozzle screens.
- Hose down the outside of the sprayer once again.
Tank Rinse Nozzle Suppliers
Spraying Systems (TeeJet) www.teejet.com/techcent/ catalog_english/spec_fert.pdf
Sample layout of a sprayer rinse system
Two types of 360-degree tank rinse nozzles
- Cornell Cooperative Extension. (2002.) Pest Management Guidelines for Commercial Tree Fruit Production.
- DuPont Agricultural Products. (1995.) A Guide to Application Equipment Cleanout for DuPont Sulfonylurea Herbicides. DuPont Agricultural Products.
- Hardi International web site:
- Harrison, Scott and Hock, Winand. (N.D.) Agrichemical Fact Sheet #9 - Options for In-field Pesticide Sprayer Rinsing and Clean Water Utilization. Penn State Cooperative Extension.
- Johnson, Bill, etal. (1997.) Cleaning Field Sprayers to Avoid Crop Injury, Fact Sheet G 4852. MU Extension, University of Missouri - Columbia.
- Peterson, Dallas E., Kuhlman, Dennis K., and Devlin, Daniel L. (1998.) Cleaning Field Sprayers. Kansas State University Department of Agronomy.