Calibration of In-Furrow Sprays

As we finally move into drier conditions and cotton planting is starting full swing, more and more folks are adopting in-furrow sprays for thrips control. We have had several questions regarding calibration of in-furrow sprays. Below are are few tips to consider for proper calibration of in-furrow sprays.

First lets go over a broadcast example before moving to in-furrow sprays:

Calibrating broadcast sprayers: There are many ways to calibrate sprayers. The following is one of the commonly used formulas.

MPH x NSI x GPA

GPM = —————————-

5940

• GPM= Gallons per minute
• MPH= Miles per Hour
• NSI= Nozzle Spacing in Inches (or band width)
• 5940= this is a constant

What this formula tells you is how many gallons you would have to catch in one minute (GPM) going X miles per hour (MPH) with X nozzle spacing (NSI) to deliver X gallons per acre (GPA).

Here is an example: A farmer wants to drive his sprayer 5 MPH.  His boom has each nozzle spaced 20 inches apart and he wants to apply 10 gallons of solution per acre.

5 x 20 x 10                                 1000

GPM = ———————     =                    ——-      =         0.16835 (Gallons Per Minute)

5940                                   5940

So you would have to catch 0.16835 gallons in 1 minute to deliver a rate of 10 gallons per acre driving 5 miles per hour with your boom set up on 20 inch nozzle spacing.

Because measuring 0.16835 gallons is not feasible, convert that number into a smaller unit like ounces. Because there are 128 oz. in one gallon, we can simply multiply 0.16835 by 128 which equals 21.5 ounces needed in one minute. Most people will take the 21.5 oz. and divide it by 2 so they only have to catch for 30 seconds rather than 1 minute (11 oz.) or divide it by 4 and only catch for 15 sec (5.4 oz.).

In-furrow calibrations: Calibrating in-furrow sprays are not difficult but are calculated a little differently. The main difference with in-furrow spray calibration is you use the row width in inches in the NSI part of the formula.

Example:

• 38″ inch rows
• 3 Gallons/Acre
• 4.5 MPH

4.5 x 38 x 3                                 513

GPM = ———————     =                    ——-      =         0.08636 (Gallons Per Minute)

5940                                   5940

So you would have to catch 0.08636 gallons in 1 minute to deliver a rate of 3 gallons per acre driving 4.5 miles per hour with your row spacing of 38 inches.

Again, because measuring 0.08636 gallons is not feasible, convert that number into a smaller unit like ounces. Because there are 128 oz. in one gallon, we can simply multiply 0.08636 by 128 which equals 11.06 ounces needed in one minute. Most people will take the 11.06 oz. and divide it by 2 so they only have to catch for 30 seconds rather than 1 minute (5.53 oz.) or divide it by 4 and only catch for 15 sec (2.77 oz.).

As an example if you intend on applying Admire Pro at a broadcast rate sprayed in-furrow of 9 oz/acre + Acephate at .75 lb/acre, for every 3 gallons of water you put in the tank, add 9 oz of Admire Pro and .75 lb of Acephate.

For a more detailed explanation of calibration please see the following publication: Pesticide Calibration Made Easy