LOVELOCK - This last week I have seen a few farmers spraying their fields to prevent unwanted weeds in their alfalfa crop. There is no better time than early spring to take a closer look at your sprayer to make sure it is operating correctly, this includes homeowners that use small lawn sprayers.
The following are some of the things you should check on a sprayer to achieve efficient and effective application of pesticides:
• Double check your sprayer for mechanical problems before you start using it. You may not have time to do this later.
• Clean the sprayer tank thoroughly and make sure nozzle filters are clean.
• Clean spray nozzles, check their flow rates, and replace the ones that are spraying more than 10 percent of the original output.
• Check the agitator in the tank to make sure it's working properly.
• Run water through the spray system to make sure everything is working properly
• Find out if the sprayer is delivering the proper application rate (gallons per acre).
One can determine if the chemicals are applied at the proper rate only by carefully calibrating the sprayer. Calibration, perhaps more than anything else, will have a direct impact on achieving effective pest control and the cost of crop production.
While applying too little pesticide may result in ineffective pest control, too much pesticide wastes money, may damage the crop and increases the potential risk of contaminating groundwater and the environment. Research studies show that only one out of three to four applicators are applying chemicals at a rate that is within 5 percent (plus or minus) of their intended rate.
Sprayers should be calibrated several times a year. Changes in operating conditions and the type of chemical used require a new calibration. Frequent calibration is even more important with liquid application because nozzles wear out with use, increasing the flow rate.
Approximately 67 percent of the operators who calibrated before every spray operation had application errors below 5 percent. Only 5 percent of the applicators who calibrated their equipment less than once a year (once every two, three, four years) achieved the same degree of application accuracy.
Before starting calibration, make sure you have a good set of nozzles on the sprayer. Clean all the plugged nozzles. Check the output of all the nozzles for a given length of time at a given spray pressure.
Compare output from each nozzle's output with the expected output shown in the nozzle catalog for that nozzle at the same pressure. Replace the nozzles showing an output error of more than 10 percent of the output of the new nozzle. Once you do this, now you are ready to calibrate your sprayer.
Only three things are needed to calibrate your sprayer: a watch showing seconds, a measuring tape, and a jar graduated in ounces. The following steps explain the easiest of all the methods to calibrate a sprayer.
To calibrate a boom sprayer for broadcast applications:
1. Fill the sprayer tank (at least half full) with water.
2. Run the sprayer, inspect it for leaks, and make sure all vital parts function properly.
3. Measure the distance in inches between the nozzles.
4. Measure an appropriate travel distance in the field based on this nozzle spacing. The appropriate distances for different nozzle spacing is as follows: 408 feet for a 10-inch spacing, 272 feet for a 15-inch spacing, 204 feet for 20-inch spacing, 136 feet for a 30-inch spacing, and 102 feet for a 40-inch spacing.
5. Drive through the measured distance in the field at your normal spraying speed and record the travel time in seconds. Repeat this procedure and average the two measurements.
6. With the sprayer parked, run the sprayer at the same pressure level and catch the output from each nozzle in a measuring jar for the travel time required in step 5 above.
7. Calculate the average nozzle output by adding the individual outputs and then dividing by the number of nozzles tested. The final average nozzle output in ounces you get is equal to the application rate in gallons per acre. For example, if you catch 15 ounces from a set of nozzles, the actual application rate of the sprayer is equal to 15 gallons per acre.
8. Compare the actual application rate with the recommended or intended rate. If the actual rate is more than 5 percent higher or lower than the recommended or intended rate, you must make adjustments in either spray pressure or travel speed or in both.
For example, to increase the flow rate you will need to either slow down, or increase the spray pressure. The opposite is true when you need to reduce application rate. As you make these changes stay within proper and safe operating condition of the sprayer.
Remember increased pressure will result in increasing the number of small, drift-prone droplets. Using the trial-and error method to eventually reach the intended application rate takes some time. If you follow the equations given in the Montana State University Extension Publication, "Calibrating Ground Sprayers Using Shortcut Methods" (http://msuextension.org/publications/AgandNaturalResources/MT200915AG.pdf) you can find optimum travel speed and pressure much faster.
9. Recalibrate the sprayer (repeat steps 5-8 above) until the recommended application error of +5 percent is achieved.
Sources:
Boom Sprayer Calibration, AEX-520-92, H. Erdal Ozkan, Professor and Extension Agricultural Engineer, Food, Agricultural and Biological Engineering Department, The Ohio State University.
Calibrating Ground Sprayers Using Shortcut Methods, MT200915AG, Cecil Tharp, Pesticide Education Specialist, Montana State University Department of Animal and Range Sciences.
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