If rainfall occurs soon after herbicide application, it can affect the effectiveness of postemergence herbicides. And they each differ in their time requirements for rain-free periods following application. This 2-page fact sheet shows rainfast time for postemergence herbicides commonly used in the Everglades Agricultural Area for sugarcane and vegetable production. Written by D.C. Odero and published by the UF Department of Agronomy, August 2011. (Photo by Eric Zamora UF/IFAS)
http://edis.ifas.ufl.edu/ag359