One of the most common pieces of equipment used to apply herbicide to invasive or noxious weeds is the backpack sprayer. This versatile sprayer offers users important advantages. It allows an applicator to selectively treat target vegetation, thereby reducing the risk of non-target damage. A backpack sprayer also is simple to operate and relatively inexpensive to purchase and maintain. Finally, a backpack sprayer’s portability means it can be used anywhere an applicator can reach by foot, including difficult terrain. However, a backpack sprayer must be properly calibrated and maintained to realize these benefits.
Calibrating your sprayer involves a simple process. Before you begin, remember that 1 gallon is equal to 128 fluid ounces. Therefore, the calibration area where you will spray should be sized to 1/128 of an acre. This will ensure that the fluid ounces collected during calibration equals gallons per acre.
To start, make sure your sprayer and nozzle are clean, and fill your tank with clean water. Spray some water on a surface to ensure the nozzle is working properly. If you’re using an adjustable nozzle, set and mark the selected spray pattern to ensure consistent nozzle settings throughout the calibration process.
Measure an area 18.5 by 18.5 feet, or 1/128 of an acre, in a field where you intend to spray. Time the number of seconds it takes to spray the measured area uniformly using a gentle side-to-side sweeping motion with the spray wand. Repeat this step, and average the two times.
Maintaining a constant sprayer pressure, spray into a container for the average time you just calculated, and measure the number of fluid ounces in the container. This number is equal to the number of gallons per acre the sprayer is delivering. For example, if you collect 3 fluid ounces of water in your container, your sprayer will deliver herbicide solution at a rate of 3 gallons per acre.
Backpack sprayers also are easy to maintain. Most important, applicators should thoroughly clean their sprayers after every use. This is as simple as rinsing the equipment at the end of the day using clean water or a tank cleaner. This will prolong its lifespan and cut down on the amount of repairs needed.
Care should be taken with any herbicide left in tanks — consult the herbicide label for more information.
If you’re in a colder climate, it’s also essential to winterize sprayers before cold storage. This can be done by adding automotive or RV antifreeze to the tank to prevent freezing.
Finally, if recommended by the manufacturer, be sure to lubricate all seals and O-rings at the start of the spray season. Lubricate them again midseason if the unit sees heavy use.
Calibrating and maintaining your backpack sprayer will ensure more consistent results when applying herbicides.
Article provided by Dow AgroSciences. This article originally appeared in “Vistas,” a publication of Dow AgroSciences, and is reprinted here by permission. For more information, including how-to videos on calibrating backpack sprayers, visit www.vegetationmgmt.com.