All of the following statements concerning pesticide vaporization are true except which?

• A. Pesticide vapors can cause plant injury
• B. High temperatures can increase vaporization
• C. Some pesticide vapors can drift a great distance
• D. Volatile pesticides should be applied during the warmest part of the day

Answer: (D)

Vaporization of pesticides rises with temperature, so understanding how heat affects volatilization helps explain where problems come from. When temps are higher, a greater portion of a volatile pesticide becomes vapor, increasing the chance that these vapors will move with air currents and affect areas beyond the target. Vapors can indeed cause injury to plants if they come into contact with sensitive tissues, especially when they are present in high concentrations or linger in the canopy. Some pesticide vapors drift a great distance, depending on weather conditions like wind speed, atmospheric stability, and humidity, which can transport vapors far from the application site. The statement that volatile pesticides should be applied during the warmest part of the day runs contrary to these dynamics; cooler parts of the day reduce volatilization and drift, making applications safer for non-target areas.