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Mark VanGessel – Extension Weed Specialist; mjv@udel.edu – April 17, 2026
Note: This article appeared in the Weekly Crop Update – University of Delaware in April, it applies to the weather conditions we are having now and into the summer.
It is unusual to talk about herbicide drift related to temperature concerns in mid-April. But here we are. Physical herbicide drift occurs as a result of droplets being deposited where they are not intended due to wind blowing them off target. Most herbicide labels have some version of the following language:•
- Drift potential is lowest at wind speeds of between 2 and 10 miles per hour
(many companies are using 10 mph wind speed as the cutoff for applications). However, many factors, including droplet size and equipment type, determine drift potential at any given wind speed. - Avoid application when wind speeds are below 2 miles per hour due to variable wind direction and the high potential for temperature inversions.
- High temperatures and low relative humidity are conditions that allow evaporation to reduce droplet size and increase the potential for drift. Select nozzles and set application equipment to produce larger droplets to compensate for evaporation. Droplet evaporation is most severe when conditions are both hot and dry.
Some of the Group 4 herbicides (2,4-D and dicamba) have the potential to volatilize at high air temperatures. This occurs when the spray droplet lands on the leaf or soil and then it is converted into the gas or vapor phase that can move off target. Temperatures above 85 create conditions that favor volatilization. Water on the soil and/or leave surface at time of application increases the risk of volatilization. The new versions of the dicamba products for Xtendimax soybeans address this by limiting applications during periods of high temperature (above 85). The guidelines on the labels include:
High temperatures and low relative humidity are conditions that allow evaporation to reduce droplet size and increase the potential for drift. Select nozzles and set application equipment to produce larger droplets to compensate for evaporation. Droplet evaporation is most severe when conditions are both hot and dry.
Some of the Group 4 herbicides (2,4-D and dicamba) have the potential to volatilize at high air temperatures. This occurs when the spray droplet lands on the leaf or soil and then it is converted into the gas or vapor phase that can move off target. Temperatures above 85 create conditions that favor volatilization. Water on the soil and/or leave surface at time of application increases the risk of volatilization. The new versions of the dicamba products for Xtendimax soybeans address this by limiting applications during periods of high temperature (above 85). The guidelines on the labels include: - DO NOT apply if temperatures are forecasted to be 95 °F or above either on the day of treatment OR the day after treatment at temperatures ≥ 95 °F. •
- If temperatures are forecasted to be 85 to <95 °F on the day of treatment or the day after treatment, limit application to no more than 50% of the total number of dicamba- resistant soybean acres managed by the grower within the county within one day. Remaining untreated 50% of dicamba-resistant crop acreage managed by the grower may be treated on the third day after initial treatment.
The above restrictions for volatilization are only on a few dicamba products, but they should serve as guidelines for application all dicamba products as well as 2,4-D ester and amine formulations.
Any pesticide that moves off target (either through drift or volatilization) cannot do the job it was intended for, controlling the pest in your field.