How To Calibrate Your Sprayer: Handheld or Spot Application
Calibrating Your Sprayer for Spot Application
If you’ve been following your GDD Tracker, or watching the Forsythia and other plants flower and begin to leaf out, you know that for much of the Midwest it’s time to put away the preventative crabgrass treatments and move towards post-emergent broad-leaf control.
Most of you will be utilizing some sort of small-volume, single-nozzle sprayer throughout the growing season to spot spray. This could be a hand-held pressurized tank, a backpack sprayer, or a larger tank on the back of a utility vehicle. For each different tank and operator, you will want to calibrate your sprayer appropriately to ensure you are not under-applying or over-applying product.
The good news – this doesn’t take long. You can do quickly in the morning before going out into the field.
The Label Is The Law
Follow your label. Take a few minutes of extra time to read it carefully. Even if you’ve done this a thousand times, double check. Rushing isn’t worth the headache it could cause you later.
For our purposes in this article, I’m going to use a real-life label of 2,4-D. Please find the label here and use it as a reference as we move forward. (Using this label is not an endorsement from The Campus Green, it’s just the first good one I found in a Google search).
Step 1: How Much Chemical To Use
Our label is incredibly helpful here. Go to page 9 and see the application rates when applying to ornamental turf. We will assume we are applying this 2,4-D in our lawn and use these rates. We will also assume we are applying to well-established turf and use a rate of 3 pts/Acre.
As a bonus, this label even has a useful chart on page 5 that tells us 3 pt/Acre equals 1 oz/1,000 sq ft. If you didn’t have this chart, you can figure it out yourself. If you’ve never memorized how many ounces are in a pint, don’t worry. You live in the golden age of Google – look it up. And you find:
1 pint = 16 fluid ounces.
1 Acre = 43,560 sq ft (or 43.56 M – I’ll use M for 1,000 sq ft to make this easier to read)
In our example, we need to spread 3 pints over an Acre, or 48 ounces over 43.56 M. So we just divide:
48 ÷ 43.56 = 1.1 oz/M.
Look, we’re being more accurate than the label! Isn’t that exciting!
Step 2: How Much Carrier To Use
That’s great, but we need to know how much water to use.
Similar to calibrating your spreader, you simply need to set up a course that covers a measurable area.
I like to set up a course that measures exactly 1,000 square feet. I’ve had plenty of operators suggest that we cut the course in half and only measure 500 square feet, but I think the larger course gives us better accuracy.
Start by finding your swath-width of your sprayer. For handheld sprayers, this is simply the width of the spray as the operator moves their arm back and forth. I just measured my own swath-width at seven feet. To make a 1,000 square foot course, I need to mark off 7′ x 143′ (1000 ÷ 7 = 142.9) or if I don’t have a 143′ stretch, I measure twice my swath-width at 14′ x 71′ (1000 ÷ 14 = 71.4) and run the course down-and-back. Find the nearest parking lot and measure out your course.
Now that you have 1,000 square feet clearly defined, fill your sprayer with clean water, and apply the water to the pavement the same way you would apply the herbicide to the turf. Time yourself (or better yet have someone else time you) to see how long it takes for you to finish wetting all the pavement in the course. Remember to keep as many conditions identical to the field as possible. Walk backwards (never walk through your chemical) keeping a steady back-and-forth motion with your arm and maintaining consistent swath-width.
A bonus to spraying water on the pavement is you can see the gaps in your application and adjust your technique accordingly. You can also spot problems with your nozzle or inconsistent pressure – they all show up in the spray pattern on the pavement.
How long did it take you to finish your course? However long that was, you need to now spray water into a bucket for that long to see how much water the course took. Measure the water at the end. However many gallons of water you have in the bucket is how much water you use per 1,000 sq. ft. (For illustration purposes, I’ll say I used 1.5 gallons of water).
Remember: If you cut your course in half, remember to double your water volume to get gallons/1,000 sq ft.
Step 3: Mix Your Tank
Now you have all the data you need to mix your tank. You know how much chemical to use and how much water to use per 1,000 square feet. For my sprayer, my nozzle, on my site, I need to mix 1.1 oz. of 2,4-D per 1.5 gallons of water. This amount will vary as I change operators, nozzles, sprayers, and even caffeine levels in the morning – please re-calibrate regularly to ensure accuracy.
Note: You’re smarter than this, but please don’t use MY numbers, find your own. I need to say this so I don’t get angry emails from people who should have known better.
Step 4: Apply
You can now apply your material with confidence, knowing you are accurately calibrated. Do this once or twice and it will be easy. Remember to clean your tank appropriately before using again, and before re-calibrating on pavement to avoid runoff. Follow your label and local laws, use proper PPE, stay safe, and enjoy your well-calibrated sprayer as you keep better grounds.