MSU Extension Michigan Fruit Management Guide

Accurate calibration is the only way to ensure that a sprayer is applying the intended amount of chemical. The operator must know the amount of water that will be applied per unit of area to make a proper spray mix. Failure to calibrate a sprayer can result in crop injury, creation of a hazardous situation and wasted money. Frequent calibration identifies worn nozzles and keeps the operator aware of factors affecting application rate, such as travel speed, pressure and type of nozzle in use.

Precalibration check

Before calibrating, check the sprayer carefully. Be sure the nozzle tips are clean. Replace all worn or damaged nozzles. Check all hoses and fittings for leaks and aging. Make sure that the pressure is constant and the tank is free of dirt and debris.

Determining sprayer speed

The rate of travel needed for proper distribution of spray within the canopy can be determined by trial by placing water-sensitive spray paper at various locations within the canopy or trellis.
For proper pesticide application, the air within the canopy must be completely replaced with spray-laden air from the sprayer. In general, a travel speed of 1 to 3 miles per hour has proved satisfactory, depending on the size and density of the canopy and the capacity of the sprayer. Before a sprayer can be calibrated, the travel speed must be determined in miles per hour (mph). To determine the travel speed, load the sprayer with clear water and make a test run in the orchard or vineyard. Always make the test run on similar ground — tractor speed changes dramatically from soft to firm surfaces. Set the tractor throttle at a level sufficient to operate the sprayer (PTO speed) and select an appropriate gear. Remember or mark these settings. Speed can be calculated by measuring the time required to travel any measured distance. A good conversion factor to remember is that 1 mph=88 feet/min. A convenient test length is 176 feet because it is a multiple (2x) of 88. The following formula can be used to determine travel speed:

Speed (mph) = distance (ft) x 60 / time (sec) x 88

For example, if it requires 60 seconds to travel a measured distance of 176 feet, the travel speed is:

mph = 176 x 60 / 60 x 88 = 10,560 / 5,280 = 2 mph

Determining nozzle flow rate

To select the correct nozzle and whirlplate sizes, the total gallons per minute (gpm) of output for each particular application must be determined. To determine gpm, it is necessary to know the travel speed of the sprayer (mph), the gallons per acre (gpa) to be applied and the spacing (W) between the rows of plants. Once these three variables are measured or selected, a simple equation can be used to calculate the gpm. This equation is for one side of the sprayer manifold only. Double the calculated answer if both sides of the sprayer are to be used. Once the nozzle and whirlplate combinations are determined, place the same size nozzles and whirlplates in both sides of the sprayer if both sides are to be used.

Step 1. 

Calculate the total gpm required per side

Step 2.

Select the correct nozzle-whirlplate combination and operating pressure. Air-blast sprayers normally use disk-core-type cone spray tips. The correct size nozzles and whirlplates can be selected by using a table, which indicates the nozzle size and gallons-per-minute output at various pressures using specific whirlplates. These tables can be found in the sprayer manufacturer’s literature or in nozzle catalogs. Nozzles in the sprayer manifold should be arranged so that approximately two-thirds of the total flow comes from nozzles in the upper half of the manifold, and one-third of the total flow comes from nozzles in the lower half. Adjust nozzles this way to provide uniform coverage throughout the canopy. It should provide adequate penetration to the top and center of the canopy while avoiding excess application in the lower outside areas.

Step 3.

Install the nozzles in their proper outlets. Inspect and clean all nozzles and outlets and determine that the sprayer is operating correctly. Nozzles are a very important part of the sprayer; if any defects or wear is showing in the nozzles, replace them

Step 4.

Measure the total gpm from all the nozzles selected in Step 2. Fill the sprayer tank at least half full. Prime the sprayer system and check all the nozzles to make sure none are clogged or partially clogged. Record the exact level of water in the spray tank. Bring the sprayer up to the desired pressure and turn the nozzles on. Use a stopwatch to record how long the sprayer is running. The sprayer should be operated for at least 3 minutes. Record the new level in the tank or measure the amount of water needed to refill the tank to the original level.