Calibrating Backpack Sprayers for Small Plot Work

Backpack or knapsack sprayers are often overlooked in our world of self-propelled field sprayers and multi-row airblast sprayers. But, it’s the humble backpack sprayer that’s used in much of the worlds agriculture, and it’s still the sprayer of choice for the small plot work that leads to our North American pesticide labels.

Generally, calibrating such a sprayer requires three pieces of information:

  1. The walking speed of the operator
  2. The width of the swath
  3. The collective output per minute

But, a calibrated backpack sprayer doesn’t help someone design their small plot trials. We know this, because we receive the same questions every spring. Here are the big ones:

  • How long do I spray before I have sprayed my target volume?
  • If I walk at speed X, and I want to spray volume Y, which nozzles should I use?
  • The pesticide I’m testing has a rate based on an acre or hectare. How do I know how much I need on my plot?
  • I’m spraying trees/bushes/vines… Do I use a dose by planted area, or based on the size of the canopy?

In an effort to help operators help themselves, we have developed a small plot calculator in Excel that will answer all these questions and more.

You can download it right here:

DOWNLOAD CALCULATOR

Just be sure you’re using the right piece of equipment to perform your experiment. Try to match spray quality and method to that of the grower to ensure your results are relevant.┬áThere are already excellent resources available for the backpack sprayer operator, so there’s no reason to write a long article on the subject. Here are a few we recommend you read:

  1. Calibrating a Knapsack Sprayer (www.weedfree.co.uk – 2008)
  2. Don’t Overlook Backpack Sprayers (John Grande, Rutgers)
  3. Hand Sprayer Calibration Steps Worksheet (Bob Wolf, Kansas State University – 2010)
  4. Sprayer Calibration Using the 1/128th Method for Motorized Backpack Mist Sprayer Systems (Jensen Uyeda et al., University of Hawai’i – 2015)