August 7, 2003

 

New Spray Drop Size Classification System Developed for Nozzles

Knowing the size of drops produced by spray nozzles can help applicators determine the correct nozzle to use for a specific pesticide. That information has not always been available to applicators. According to Vern Hofman, a North Dakota State University Extension Service agriculture engineer, a classification system is beginning to be used to define drop size output for proper nozzle selection.

Nozzle manufacturers are using a standard classification system to indicate the drop size of their nozzles for different sized orifices and pressure combinations, Hofman says. The standard system was produced by ASAE (American Society of Agricultural Engineers), and contains six color-coded drop size categories. The categories are:

• Very fine–red
• Fine–orange
• Medium–yellow
• Coarse–blue
• Very coarse–green
• Extremely coarse–white

This standard is based upon the volume median diameter of the drops produced from a nozzle and is similar to average drop size. Volume median diameter is a droplet size diameter which indicates that half of the spray volume is in drops smaller than this number and half of the spray volume is in drops larger than this number.

The very fine and fine categories typically contain a considerable amount of driftable fines in the 100-micron and smaller range. Hofman says the larger drop size categories contain some driftable fines, but less in each step down the list. "Even the extremely coarse size category contains a few fines and may cause drift downwind if a susceptible crop is present or if spraying is done in a strong breeze," Hofman says.

Pesticide product labels are beginning to use the system to provide applicators with drop size information. An applicator can look at the nozzle manufacturer's chart and select the best nozzle and operating pressure for the application.

All nozzle manufacturers have classification charts for their nozzles available based on the ASAE standard. Hofman suggests that applicators contact their nozzle suppliers and request a copy of their spray tip guide. The information may also be found on the nozzle manufacturer's website.

"The classification system allows the applicator to use many different combinations of nozzles and pressure settings to achieve the desired drop size, reduce drift, and provide adequate coverage required for control of the pest," Hofman says.

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Source: Vern Hofman, (701) 231-7240, vernon.hofman@ndsu.nodak.edu
Editor: Stephanie Renner, (701) 231-8371, srenner@ndsuext.nodak.edu

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GRAPHIC - text version

ASAE Nozzle Classification System
color-coded drop size categories
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Very Fine.............Red
Fine..................Orange
Medium................Yellow
Coarse................Blue
Very Coarse...........Green
Extremely Coarse......White
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