If rainfall occurs soon after herbicide application, it can affect the effectiveness of postemergence herbicides. Certain postemergence herbicides differ in their time requirements for rain-free periods (rainfast) following application. The exact time required to protect herbicide activity and efficacy will vary with weed species, environmental conditions, and other factors, including the type of adjuvant added to the spray mix. It is important to always READ THE LABEL instructions on rainfastness before applying postemergence herbicides during periods when rainfall is frequent. For more information on rainfastness and pesticide use, see the EDIS publication PI238 – Rainfastness of Pesticides (https://edis.ifas.ufl.edu/pi238).
The table below (Table 1) shows the required time interval between herbicide application and rain-free period for postemergence herbicides commonly used in sugarcane and vegetable production in the Everglades Agricultural Area and the surrounding region.