Spray Today?

There are several very important factors to consider before deciding whether the day you have chosen to spray is the right choice for insuring your herbicide application is both effective for eliminating the weed species affecting your crops, and is safe for you, for other crops and livestock, and the environment. Before you decided whether today is the best day for spraying, please review the following information:

  • Mid-morning and early evening are the recommended times of day for herbicide application.
  • Night time spraying is NOT recommended.

The weather that really matters is the actual weather on the day and at the time when you plan to spray.

  • Check for excessive rainfall — if it has rained heavily immediately prior to the scheduled spraying day or there is excessive rain forecasted in the days immediately following the chosen spray day, it would be advisable to reschedule spraying for another day.
  • Avoid a day that is excessively calm with high humidity, heavy dew, fog or with dust hanging in the air. These weather conditions can cause inversion, which creates a condition whereby small droplets of herbicide tend to hang in the air, increasing the possibility of herbicide drift and decreasing the effectiveness of the application.
  • Avoid an excessively windy day (winds in excess of 10 mph).
Recognizing Inversions by Dr. Larry Steckel

  • The recommended wind speed should be between 3 to 10 mph. This light wind should be blowing away from sensitive areas.
  • A brisk wind will increase the possibility of herbicide drift to herbicide sensitive crops or pasture areas. A perfectly calm day may cause inversion, in which small droplets of herbicide are suspended in the calm air for long periods of time, reducing the effectiveness of the spray and the possibility of drift, if a wind should pickup during the day.
  • Should the wind increase substantially while spraying, or the day becomes completely calm with fog or dust hanging in the air, it is recommended to stop spraying and to continue spraying on a day in which the weather conditions are more favorable.
  • It is very important to check the local forecast for wind conditions, or purchase a hand-held wind measurement device to check for wind speed. If using a measuring device, check for 2 minutes and check in an area where there are no obstacles that may adversely affect the measurement. Also, check the wind speed before spraying, during spraying, and after spraying. Should the wind increase while spraying, stop and resume when the wind calms.
How to measure wind speed for herbicide application

  • Be aware of the proximity of sensitive crops.
  • Carefully read the herbicide label instructions. Labels are a value resource because they list which weed species the product targets and recommended application directions.
  • Be aware of the potential volatility of the herbicide you choose. “When growers decide on herbicide products, they should consider weed species present, weed height and crop growth stage.” (T. Legieter and B. Johnson, Timing, Product Choice Important for Postemergence Herbicide Applications. https://www.extension.purdue.edu/clark/Pages/article.aspx?intitemID=5139)
  • Keeping a journal of spraying applications will be very helpful in establishing a record of which fields were sprayed with what herbicide and which crops are tolerant or intolerant/resistant/sensitive of what herbicides. The Tennessee Department of Agriculture (TDA) has a an approved dicamba record keeping form available for growers’ use.
  • Use a separate sprayer for pastures and hay fields.
  • Check current and forecasted weather for cold, wind, rain and heavy dew before scheduling when to spray.
  • Carefully check sprayer calibration and make necessary adjustments to minimize drift.
  • Be aware of potential run-off into sensitive areas or irrigation waters.
  • Maintain a downwind buffer between the last treated row and the nearest downwind field edge (in the direction the wind is blowing).
  • Inform your neighbors of your plans.