Since we are expecting heavy rain event on Saturday, plus about to be done with the critical time for cluster infection by downy mildew, powdery mildew, and black rot (which last 4-5 weeks after bloom), I received a several emails about the application timing.
As with other timings, it really depends on so many factors, but here’s my take on it.
If you have a history of black rot and downy mildew in your vineyard, you may have a higher disease risks. If you are in this situation, AND if you think that your previous application was waring off, then you may need to apply some protection before the rain. However, if your previous application was within 7-day or have not seen many rains, or not having much issue with downy or black rot, then you probably do not need to panic.
A good news is that it looks like we have an opening after the Saturday’s rain event. (then a few more days of rain in the early part of the week) Thus, unless if you have in the high risk situation, I think you can wait until the rain is over. Then the question is what to apply, and here’s my two cents.
If you have black rot issues:
Mancozeb + Sulfur + DMI (Rally, Elite, etc) or Mancozeb + Sulfur + QoI (Abound, Pristine, etc)
It depends on how many times you have used either DMI or QoI, please limit the use of them to 2-3 times per season, and less is better due to their risk against fungicide resistance. Also, this is most likely to be one of the last application timing for mancozeb due to its 66-day PHI. If you cannot use mancozeb, use captan or fixed copper, or other downy mildew material (Zampro, Ranman, etc please see below), but make sure to tank mix with either DMI or QoI, since captan, copper, and these downy mildew materials does not have much efficacy against black rot pathogen.
If you have downy mildew issues:
Mancozeb + Sulfur + Phosphorous acid (Prophyt, Phostrol, etc) or Mancozeb + Sulfur + Ridomil (Gold MZ or Copper)
Once again, the choice depends on how many times you have used either Ridomil, please limit the use of them to 1-2 times per season, less is better. Prophyt is less prone to have fungicide resistance issues than Ridomil, but as usual, don’t rely on it too much. It has its own issues such as phytotoxicity. Also, even if your main target is downy, do not forget to add a material for black rot. It can sneak up on you!
The other newer downy mildew materials such as Revus, Zampro, Ranman, etc., are excellent materials, but they work as protective manner, thus, you cannot expect a kick-back activity with them, but with the expected rains in next week, it maybe a good idea to add these materials to the tank, in addition to the Phosphorous acid or Ridomil, especially if you do not want (or cannot) use mancozeb (but it will be an expensive spray!)
If you have concerns on both black rot and downy mildew, you can mix and match. Also, if your vines are about to be bunch closure (some of our cultivars are), do not forget to add a Botrytis material (Rovral, Vanguard, etc).
On the plans above, I am adding sulfur for powdery mildew. Since we had many rain events, I think many of you have not seen many powdery mildew, but it is a good idea to have sulfur as an insurance. If you have seen powdery, especially on clusters, you can use a potassium salt product (Kaligreen, Armicarb, etc.) which should stop the spread.
We are almost done with the critical time! Good luck!
