Weather Conditions When Spraying

Nothing affects pesticide applications as much as weather conditions while spraying. Weather may change through the course of the day, so be sure to watch if conditions deteriorate so that applications should stop.

• Wind speed and direction. Application wind speeds should be between 2 and 10 mph and blowing away from sensitive areas. A handheld anemometer will help monitor wind speed before and during application.
• Rainfall. Most insecticides are effective once the product has dried on the foliage. Some products require longer drying times, and this information will be provided on the label. Be sure to track approaching showers so you can stop spraying in time and materials are not washed off of trees before they have a chance to work.
• Air temperature and humidity. The air temperature will determine how quickly spray droplets will dry. High temperatures and humidity may also result in phytotoxicity and foliage burn.
• Time of day. In the mountains, airflow up or down slopes can affect spray deposition, especially with airblast mistblowers. In the evenings and night, the air is typically settling towards the ground, and the spray will remain in trees.