In order to use a postinfection program you must be able to monitor the environment to determine when infection periods occur. If growers do not have the capability to accurately monitor the environment, they should not use a postinfection program. This requires a great deal of knowledge about the biology of the pathogen. There are also predictive capabilities for powdery mildew and downy mildew, and Botrytis bunch rot. Predictive programs are currently being developed and evaluated for these diseases.
Timing is critical.
In most situations, once symptoms develop the damage is done.