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Announcing New Backpack Sprayer Calibration Forest Science Fact Sheet

Posted: April 17, 2017

Penn State Forestry Extension has just released the fourth in a series of Forest Science Fact Sheets.

The latest in the series, entitled Backpack Sprayer Calibration Made Easy, provides in-depth practical information on calibrating backpack sprayers for both band applications and spot treatments. The fact sheet was written by Dave Jackson, Penn State Forest Resources Educator, Art Gover, Penn State Wildland Weed Management, and Kimberly Bohn, Penn State Forest Resources Educator.

“Calibration” simply means determining the output of a sprayer so a known amount of spray solution is applied to a given area. Applicators must know this if they wish to apply an herbicide at a specific dosage, for example, ounces or quarts per acre. Failure to calibrate spray equipment can result in misapplication of herbicides, repeat applications, damaged non-target plants, excess costs, as well as environmental concerns.

This fact sheet presents a simplified process for calibrating a backpack sprayer known as the “ounces to gallons” method. With this method, the amount of spray, measured in ounces, converts directly to gallons per acre.
Band applications are fixed-width, fixed-speed applications in which the applicator treats larger, continuous areas of vegetation. In forestry applications, band treatments are commonly used for spraying interfering plants such as hay-scented and New York fern. Band applications may also be used to treat weeds along fence lines and trees planted in rows.

Spot treatments are for discrete targets scattered about a site, such as a single shrub or patches of continuous vegetation. This is probably the most common use of a backpack sprayer. This type of treatment is common when controlling invasive shrubs such as multiflora rose, honeysuckle, and autumn olive. Calibrating for these types of treatments allows the applicator to estimate spray coverage so the mix will be effective without over- or under-applying.
Taking the time to calibrate the application will ensure the proper dose of herbicide. Although calibration represents an “extra” step and time you believe you may not have, it’s not true. Applications cannot be made correctly without first calibrating. Applicators who master calibration gain a valuable skill and take control of the process rather than simply mimicking instruction that may be incorrect.

This fact sheet is available online or in hard copy by contacting the Penn State Extension Ag Publications Distribution Center at:

Phone: 877-345-0691 or
E-mail:

The publication can also be found online.