I received the same questions from several growers, so, here’s my two cents. It seems that the current rain events will end by Sunday, or at least we have a window. This event most likely results in downy mildew and black rot risk events. Although it has been dry and we probably don’t have as much accumulation of pathogens as typical year, it is probably better to have kick-back materials in your next spray.

For downy mildew, you can use either phosphorous acid (phosphonate, Prophyt, Phostrol, etc. FRAC group P07) or Ridomil Product (Ridomil Gold MZ (group 4 + M3) or Ridomil Copper (group 4 + M1). If you have Ridomil Gold MZ, make sure that you have enough days before harvest since its PHI is 66-days due to mancozeb.

For black rot, you can use one of DMI fungicides, such as Rally, tebuconazole, Mettle, Rhyme, Ceyva, etc. The DMI (FRAC group 3) is often included as a pre-mix (e.g., Revus Top (40 + 3), Inspire Super (9 +3), Viathon (P07 + 3), etc.)

These kick-back materials are effective when you apply it within several days (say, up to 3-4 days) after the rain. Since we already had nearly two days of rain, it would be a nice idea to spray them as soon as you have safe spraying condition. Hopefully, it will happen this Saturday or Sunday. There is no need to spray in the rain, because sprayed materials will be washed off.

The other downy mildew and black rot materials are preventative and need to be applied before the rain (e.g., mancozeb, captan, Revus, Ranman, etc.) You can still use them in the next spray for forward protection, but if you are thinking of kick-back, you need to use the materials mentioned above.