Backpack Sprayer Calibration for Spot Applications

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- [Emily] Backpack sprayer calibration for spot applications.

Backpack sprayers equipped with an adjustable cone nozzle are commonly used for spot applications.

The goal of a spot application is to spray the foliage of scattered individual plants or patches of plants.

To properly conduct a spot application, first practice your spray technique.

Fill your backpack sprayer with clean water and add indicator dye.

It's best to practice on the types of vegetation that you'll be treating from small plants to large shrubs.

Spraying actual plants will help you develop consistent spray coverage across various plant growth forms.

Adjust the spray nozzle to a mid-range setting that produces a somewhat solid cone.

Aim for light coverage where individual spray droplets can be seen evenly distributed across the foliage.

This is best achieved by spraying in short bursts rather than holding the trigger open.

If the spray is running off the leaves, you are applying too heavily.

Once you feel comfortable with spraying consistent, even coverage, it's time to calibrate.

Calibration allows you to measure the amount of spray applied to a certain area, and then calculate the application rate and gallons per acre.

An efficient method is to use a calibration area of 340 square feet.

This area is one 128th of an acre.

Since there are 128 fluid ounces in a gallon, spraying this area allows for direct conversion from ounces sprayed on the calibration area to your application rate in gallons per acre.

For example, if you spray 25 fluid ounces on the 340 square foot calibration area, that means your application rate is 25 gallons per acre.

Ideally, the calibration area should be laid out on vegetation similar to what will be sprayed in the field.

This could be an area of low vegetation on the ground or a wall of vegetation such as shrubs along a forest edge.

For the wall option, choose a height that can be comfortably sprayed and mark it with flagging.

Then calculate the length of the calibration area.

For example, if you choose a height of seven feet, 340 divided by seven equals 48.5, so the length of the calibration area would be 48 and a half feet.

To calibrate on the ground, choose a comfortable width and then use the same formula to calculate the length.

After laying out the calibration area and ensuring the spray nozzle is at the desired setting, make sure the sprayer is fully pressurized.

Then check that there is at least one gallon of colored water in the spray tank and mark the level of water on the tank.

The sprayer must be pressurized so the pump and hose are filled with water before you mark the water level.

Fill a measuring cup to a known level with water, 30 to 40 fluid ounces should be sufficient.

Spray the vegetation in the calibration area in the same manner as your practice runs.

Then using the measuring cup, refill your sprayer to the original starting level.

Use subtraction to determine how many fluid ounces were applied to the calibration area.

For example, if the cup started with 32 ounces and had seven ounces left after you refilled the sprayer to the starting point, then you sprayed 25 ounces.

This means your application rate was 25 gallons per acre.

Repeat the calibration process several times to get a reliable average of your application rate.

Now that you have your application rate in gallons per acre, you can calculate how much herbicide to include in your spray mixture based on the herbicide rate per acre found in the product label.

Sprayer Calibration is important.

Calibration takes some time upfront, but it is time well spent to ensure proper herbicide applications.