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How do you know what the Wind Speed is? (05/12/16)

The speed of the wind is that moment in time when YOU measure it with a reasonably accurate anemometer and record it. Further, that speed is only relevant for the location and that moment in time where YOU measure it.

How do you know what the Wind Speed is?

The speed of the wind is that moment in time when YOU measure it with a reasonably accurate anemometer and record it. Further, that speed is only relevant for the location and that moment in time where YOU measure it. 

As a pesticide applicator you want to know what the wind speed is when and where YOU are making the application. Without that data, complying with the pesticide label is problematic. Further, it does not matter what the speed is in New York City, New Orleans, or even Fargo.  Especially when you are making an application to a soybean field in northwestern Cass County, North Dakota. It only matters in the field you are applying in.

Too often, in haste, applicators rely on television, radio, or an internet report from a remote sensing station near the spray site. The problem is, these reports may not be in real time and they may be many miles away from where you are spraying. More important, the placement of the anemometer at a remote location may be at extreme variance to what is relevant in the field you are wanting to spray.

Placement counts:

  • If, in the example above, you hear on a commercial radio station the wind speed is X in Fargo, you will be getting a reading from the top of a 33 foot pole at Hector International Airport. Clearly, the wind speed will be much different (likely higher) than at spray boom height.
  • How about using an NDSU NDAWN station 10 miles from your field? Nope, NDAWN reports wind at 10 feet, which, with the exception of airplanes, is about five to eight feet above application height. Again the wind speed would likely be different where you are spraying.   
  • How about using your shop or home weather station? This would not be a good choice because of calibration issues. Especially because people often put the anemometer on locations well above application height. Further, garages, machine buildings, shelter trees, and grain bins can have a major impact on wind speed.

So, we have established there are issues with relying on off-site information. How about taking the measurement in the field? That is the best choice. Even so, be careful when taking readings:

  • Unfortunately, if you use a simple, analog ball and tube gauge, you will likely have accuracy problems because of dirt in the tube and more often than not, improperly holding it into the wind.
  • If you have a nice Kestrel gauge, it will work very well if it is held correctly into the wind. But if you take the measurement from the top of a high clearance sprayer, or behind a water truck, or on either side of a shelterbelt, you will likely get a reading that will not be indicative of what is impacting the spray droplet at application height. 

Best advice on determining wind speed for spraying:

  • Use offsite reports as a general indicator and for planning purposes, but do not use them as a substitute for measuring the wind in the field you are going to spray.
  • You get what you pay for. Buy and use a good digital anemometer. Plan on spending at least $80 and if you want all the bells and whistles, spend $300 plus. Handle the device with care, protect it from damage, and keep a spare set of batteries.
  • Measure wind speed at application height (approximately 18 to 24 inches above the target).
  • Location matters. Avoid taking readings at a location that will be artificially impacted by objects, like the sprayer, a truck, or a tree. 
  • Take readings hourly and record them hourly.
  • Use YOUR anemometer. A device that is in a tool box or in a coffee cup holder in a pick-up that is not being used is worse than not having one at all

Finally, where you take a wind measurement may be dictated by the pesticide labeling. Below is a sample statement:

“For all non-aerial applications, wind speed must be measured adjacent to the application site, on the upwind side, immediately prior to application”.

If you encounter this statement or something like it, follow the instruction and note the location in your records.

Andrew A. Thostenson

Pesticide Program Specialist

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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