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Doing the Math to Meet the XtendiMax, FeXapan, and Engenia Label Application MPH, GPA and PSI Requirements

The EPA recently issued revised labels for XtendiMax w/VGT, FeXapan wVGT, and Engenia.  As in 2017, these labels have specific requirements on certain sprayer operation parameters.  For instance, each label specifies a minimum GPA (ExtendiMax and FeXapan at 15 GPA and Engenia remains at 10 GPA), a maximum travel speed of 15 MPH, and also suggests or recommends adhering to the pressure ranges specified by the nozzle manufacturers for the nozzle type selected.  The original nozzle approved by the EPA, the TTI10004, was based on using the TTI11004 at a maximum operating pressure (63 psi for XtendiMax and though not listed, similar for Engenia).  The approval was based on wind tunnel testing with the droplet data entered into the AGDISP Model for the purpose of creating a drift profile.  That drift profile was then used to compare various combinations of the above dicamba products with all tank mixes including DRA's and nozzles.  In order to become approved for use, all nozzles, chemistries, and DRA's must be equal to or less than the drift profile level origianlly established for the TTI11004..  

In order to help applicators (those making decisions) and spray machine operators understand what limitations these specifications place on making applications to DT crops, I have completed a document with charts showing the math for the various options that would be possible.  Speed and pressure are typically used to determine the operating parameters for any give application scenario.  That will not change, but because of the restrictions on the label, the flexibility in making the applications will be severely limited for each combination of parameters.  This is particularly true when using conventional spray systems equipped with rate controllers.  The information included in the charts does not include PWM sprayers.

The charts will show the results of the calibration math for the GPA, MPH, and PSI options.  The calculations are for any of the approved nozzle orifice sizes (03, 04, 05, 06) and are based on 15 and 20-inch nozzle spacings.  The results will be different for each nozzle spacing. The formulas used to determine GPM and PSI are footnoted in the document.  The acceptable combinations are based on a pressure range considered appropriate (by the author) or otherwise specified in the label.  For most of the venturi nozzle types, I am using a pressure range of 40 - 65 psi (exceptions are noted).  The charts reflect speeds from below 10 MPH and at a maximum of 15 MPH.  The range for the GPA options range between 10 and 20 GPA.

The nozzle charts available on the above product websites suggests that using low operating pressures are acceptable.  I have a concern regarding the lower range of the pressures that are published with these on-line approved nozzles,  It is possible for venturi nozzle designs at lower pressures to have a poor pattern and also too large a droplet.  Sure that meets the EPA to mitigate drift, but using at low pressures may end up with inadequate coverage on the target, reducing the effective of the application.  To me that will not be good for the success of these herbicide technologies.

Using the University of Illinois Smart Phone or Tablet App - SPRAYER CALIBRATION CALCULATOR, is a very efficient way to complete all the necessary calculations for this table or any other similar calibrations needs such as this.  This app is available through Google Play or the App Store on your phone or tablet.

Links to charts:

20-inch nozzle spacing - MPH and PSI Options when Applying XtendiMax, FeXapan, and Engenia

15-inch nozzle spacing - MPH and PSI Options when Applying XtendiMax, FeXapan, and Engenia - not available at this time.