The Washington State Department of Agriculture (WSDA) reminds pesticide applicators and homeowners applying pesticides to take special precautions during this time of year when temperatures can reach 85 degrees or more. This kind of heat affects how some pesticides behave.

In hot weather, some herbicides commonly used in agriculture, for noxious weed control, on right-of-ways and by homeowners for weed control, can form a vapor and drift. To ensure these pesticides are applied properly during hot summer months, WSDA reminds pesticide applicators to take the following steps:

• Stop applying the pesticide when the air temperature reaches 85 degrees.
• Read the label on the pesticides being applied and follow all precautions and restrictions such as temperature cut-off restrictions. In Washington, some products are “Use Restricted Herbicides” and have application cut-offs which include temperatures greater than 85 degrees and three hours before sunset.
• Scout the areas bordering the treatment site before making the application. Be careful near sensitive crops and residential areas.
• Evaluate conditions such as wind speed and direction, and the potential for early morning or late evening inversions – all of these can move pesticide applications off target.

Under certain conditions, pesticide products can turn to vapor even after the application has stopped. Applicators should consider:

• Soil surface temperature, which can be much higher than ambient air temperature.
• Whether the air temperature is expected to rise above 85 degrees.
• Whether there will be temperatures higher than 85 degrees for the rest of the day.

If the temperature reaches 85 degrees early in the day, a different herbicide less affected by temperature might be a safer selection.

Applying pesticides safely is the responsibility of the applicator. When problems occur, WSDA investigates complaints alleging violations of the state’s pesticide laws, including cases of drift, worker exposure, or environmental harm. Visit www.agr.wa.gov/pestfert/pesticides for more information or contact WSDA’s Pesticide Management Division at compliance@agr.wa.gov or toll free at 1-877-301-4555.