Application of Pesticides During Periods of High Temperature and Low Humidity

We are currently looking at near drought conditions across the state of North Dakota with weekend temperatures around 90 plus degrees F in the East and over 100 plus degrees in the West. This will be a significant challenge for pesticide applicators. As usual, timing is everything and with crop and pest development advancing rapidly there is the fear that waiting for more moderate weather means reduced pesticide effectiveness. The following is the best advice I can give:

  • Consult the label(s). If there are prohibitions respect them. They are likely there because of drift concerns, efficacy problems, and/or phytotoxicity issues.
  • Observe the weather closely and make your application in the morning or early evening hours. I know, you’re saying, “but now I risk running into an air temperature inversion”. Yes that could be a problem, but most of the time wind speed and/or cloud cover will be sufficient to neutralize this concern.
  • If you decide to make the application, carefully make a record of it. In addition to all the data needed for the department of agriculture, record the humidity and sky cover as well. This will be invaluable in assessing effectiveness or lack thereof of for future applications.

In the June 9, 2016, issue of the NDSU Crop and Pest Report, I wrote extensively about potential drift problems associated with applying pesticides when temperatures are high and humidity is low. You can review that discussion at: