Boom Sprayer Setup and Calibration
Part 2, Section 1: Pest Management
Pesticides and Their Application
Boom sprayer setup and calibration
Advances in agricultural chemicals have made precise application of herbicides and pesticides much more important, not only because of the cost of the chemicals but also because of the danger of off-target spray drift. The economic impact of spray drift comes not only from the loss of chemicals that should have been applied to the crop, but also from the potential damage the chemicals may cause to adjoining crops, the contamination of surface and ground water supplies, and health risks to animals and people. Legal liability costs have been rising recently, justifying added attention to properly calibrated and operated spraying equipment.
Reasons for calibrating:
- Chemicals should be applied at the proper rate to be effective and safe without causing pollution. The calibration test tells us the application rate with our selected nozzles, pressure, sprayer design, and travel speed.
- The operator must know the application rate (from the chemical label) to determine the proper amount of chemical(s) to add to the sprayer tank. Once the actual application rate is known, it is easy to determine the acreage that a tankful or part of a tank will cover. Then, the proper amount of chemical to add to the tank can accurately be determined.
- Applying a chemical at the wrong rate is disadvantageous. Using more than the desired amount of chemical is wasteful, may violate label rates, and may pollute the environment. Too low an application rate probably will not be effective, and money will have been wasted on the material and its application.
- Actual application rates in the field may vary from nozzle catalog values, because of pressure gauge error, wheelslip, speedometer error, and friction loss in the plumbing. A catalog is satisfactory for selecting the correct nozzles, but the sprayer must be checked under actual operating conditions to adjust the pressure for the exact application rate required.
Precalibration or start-of-season checkout
- Before the spraying season or the first use of the season, the sprayer should be thoroughly checked for mechanical operation. Engines, pumps, hoses, valves, and electronic controls should be inspected, and worn parts repaired or replaced. The wheels, tank, and mechanical parts should be inspected and the equipment lubricated. Belts, pulleys, PTO shafts, and shaft guards should be checked for wear, and all guards must be in place. Consider the economic impact on the crop if the sprayer malfunctions during a critical spraying operation and parts must be ordered. Make sure the nozzle spacing on the boom is uniform. Make accurate measurements and adjust—do not estimate. Check that all nozzles on the boom are from the same manufacturer, have the same part number, and are the same size.
- The spray nozzles and all strainers should be checked. Remove strainers and make sure they are clean. Clean nozzles in soapy water with a toothbrush or a nozzle-cleaning brush. DO NOT use any hard or metallic tools to clean the nozzles. Check pressure gauges to make sure they are in calibration and reading correctly. An inaccurate pressure gauge will cause an improper application rate. This is a good time to replace nozzles. The cost of new nozzles usually is recovered within one or two spray applications. Consider upgrading to stainless steel nozzles. The sprayer owner should always purchase at least one extra or spare nozzle of the same type and size as those on the boom. This nozzle is not to be used for spraying, but only for calibration.
- Clean the sprayer tank, piping, screens, and nozzles. This is important, especially with the use of chemical-resistant crops where sprayer contamination could cause significant crop damage to nonresistant crops. A good cleanser is sudsy ammonia, which can be purchased at most grocery stores in gallon or half-gallon containers. Washing soda (sal soda), another grocery store item, or trisodium phosphate may be used. For additional information, request the Cooperative Extension fact sheet B72, Sprayer Cleaning, from your local extension agent.
In general, cleaning involves first flushing the sprayer and tank with water. Then, add 25 gallons of water to the tank and add 1 quart of household ammonia or sudsy ammonia if the tank has held organophosphates or carbamate insecticides. Ammonia will detoxify these chemicals. For other spray chemicals, to the 25 gallons of water in the tank, add 1 lb washing soda and ¼ lb powdered detergent (or enough liquid detergent) to make a sudsy solution. Two lbs of trisodium phosphate (available at paint stores or hardware stores) may be substituted for the washing soda. Agitate the solution and operate the sprayer for at least 2 minutes. Let the solution stand in the sprayer for at least 2 hours (or overnight for hormone herbicides, salt or amine formulations). Flush the cleaning solution out of the sprayer and rinse it with clean water.
After cleaning, check the nozzles and screens again, as they may have captured scale and sediment loosened by the cleaning solutions.
Before the spray activity, or especially before changing spray chemicals, clean and flush the sprayer with clean water. The proper nozzles and nozzle discharge rate, speed, and operating pressure will have been selected previously for the proper application rate.
- On an area that best represents the average topography for the area to be sprayed, measure and mark off a distance of 100, 200, or 300 feet. The goal for this operation is to calibrate the tractor's speedometer or tachometer so that the proper speed can be maintained during application.
- Fill the sprayer tank about half full of water before the sprayer speed calibration.
- With the tractor traveling at this desired spraying speed, time and record the seconds needed to travel the calibration distance.
Using the formula or the table below, calculate the actual speed driven through the calibration distance compared to the desired application speed. Adjust the speed and note the speedometer or tachometer reading until the desired speed is achieved.
Speed (miles per hour) = (Distance (feet) × 60) ÷ (Time (seconds) × 88)
Time required in seconds, to travel a distance of: 100 feet 200 feet 300 feet 0.5 136 273 409 1.0 68 136 205 1.5 45 91 136 2.0 34 68 102 2.5 27 55 82 3.0 23 45 68 3.5 19 39 58 4.0 17 34 51 4.5 15 30 45 5.0 14 27 41 5.5 25 37 6.0 23 34 6.5 21 31 7.0 19 29 7.5 18 27 8.0 17 26 8.5 16 24 9.0 15 23
Note and record the engine rpm and the gear selection, so the same speed is used during calibration and application.
_______ mph _______ rpm
_______ gear _______ range
- Place one new nozzle of the type and size to be used during the spraying on the sprayer boom in the position closest to the pump or the control valves.
- Add water to the sprayer (if necessary), engage the pump, and adjust the pressure regulator to the desired boom pressure selected from the catalog tables for the nozzle to be used. (This nozzle and desired output were determined during the precalibration nozzle selection.) Using a measuring container, collect the liquid from the new nozzle for one minute. Adjust pressure until the amount collected equals the desired nozzle output in GPM. (If your container is calibrated in fluid ounces, divide the amount collected in ounces by 128 to convert to gallons.) You have now set he correct sprayer pressure. Replace the new nozzle with the regular sprayer nozzle.
- The next step is to calibrate all of the nozzles to make sure they are within the calibration standards. Collect the output from each nozzle for 1 minute and measure the volume. If the output from any boom nozzle is less than the output from the new nozzle, the nozzle is dirty or clogged and the strainer and nozzle should be cleaned. If the volume collected is more than 110 percent of the new nozzle output (10 percent more than the new nozzle output), the nozzle is worn and should be replaced. Both the nozzle application rate and spray distribution pattern will be unacceptable for precise spraying and drift control. If more than two nozzles on the boom are 10 percent greater or less than the new nozzle rate, replace all of the nozzles on the boom, as this is an indication of excessive wear.
Setting boom height. Even with properly calibrated spray nozzles and correct pressure settings, the spray distribution pattern may not be acceptable unless the boom height is properly adjusted. The nozzle spray pattern is designed so that when the boom height is set for the nozzle spacing on the boom, the spray is evenly applied across the boom width. The boom height is measured from the top of the plant canopy to the nozzle and is specific for the nozzle spray pattern (for example, a 110-degree flat fan or an 80-degree or 60- degree spray pattern have different boom height settings). Ground level is the target for preemergence herbicides, while the top of the weeds or cover crop is the target for postemergence sprays.
The manufacturer's catalog recommends the correct boom height for each type and size of nozzle. Since individual fan nozzles deliver more spray in the middle of the patterns than at the edges, boom height needs to be adjusted so that the patterns overlap. Flat fan patterns should overlap 40% of nozzle spacing, and flooding fan patterns should overlap 50% on the target regardless of the nozzle spacing or spray fan angle.
A simple check is to spray water on a clean concrete or asphalt road or parking lot and observe the drying patterns. On a warm sunny day, the water will dry in 2 to 4 minutes. Heavy (wet) streaks under each nozzle indicate that the boom is too low. If the target is not at ground level, check the overlap at ground level and then raise the boom the appropriate amount.
A more sophisticated method is to attach strips of water-sensitive paper to boards laid across the swath width. Spray over the water-sensitive paper at normal operating conditions. The yellow paper will turn blue where each spray drop is deposited. Evaluate the uniformity by observing the portion of the paper target that changes color.
As a rule of thumb, boom height settings less than the manufacturer's recommendations will result in uneven distribution such as banding or striping. Boom height settings higher than the manufacturer's recommendations will increase the uniformity, but also increase the potential for spray drift, because of the greater distance between the nozzle and the plant.
- As a final precaution, be sure to wear protective gloves, goggles, and waterproof clothing when cleaning or calibrating sprayers or adding chemicals.