Preventing Off-Target Spray Drift: Observing Winds Speeds

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There are many factors that can affect the potential for off-target spray drift. They include the following:

  • Spray droplet size: smaller the droplet the farther it can travel.
  • Nozzle operating pressure: the higher the pressure the smaller the droplets and the farther they can travel.
  • Height of the boom: the higher the boom the more chance of drift.
  • Temperature Inversion: cooler air at the ground with warmer air higher will allow spray droplets to hover closer to the ground instead of rising.
  • The speed of the sprayer (mph): causing shearing of water into smaller droplets that can travel further.

But one other factor is wind speed. We all are very aware of how windy our area is, but I wonder if we truly understand the extent/frequency of high wind speeds. Off-target spray drift, which is the movement of spray droplets off of the site where the pesticide is desired, may be more of a problem than we realize. I selected the average wind speed for Elizabeth City for the months of June, July, and August of 2019, which is when much of our pesticide applications are made in our crops in the county.

For the year 2019 for the months of June, July, and August, the percent of days for each month that was greater than 10 mph was 36%, 25%, 13%, respectively. Especially for herbicides, many of them do not recommend spraying above 10 mph. Also, for certain herbicides, there are concerns about wind speeds below 3, which could indicate the presence of a temperature inversion.

The point that I make in all of this is that we need to be mindful of all the factors that can contribute to off-target spray drift, including wind speed. It may pay to invest in an anemometer that measures wind speed, especially so that you can document it for your auxin herbicide application records.

Average Wind Speeds

Wind Speeds