Wednesday, July 25, 2018

Reminder on downy mildew

Just a reminder on downy mildew management: although the month of July was dry until this week, many of us had a very wet early summer that fostered downy mildew development. In addition, during the last several days, the night time temperature was in low 70s and RH was 95-99%, which was an ideal condition for downy mildew spore production.

Thus, if you have not, make sure to protect your vines against downy mildew when you have a chance. If you think you have missed the window, we still have some options.

We have materials with kick-back activities against downy (Ridomil products (FRAC=4), phosphite (FRAC=P7, Prophyt, Phostrol, etc.). One of two Ridomil product (Gold MZ) has a mancozeb, which has a 66-day PHI, so, unless you have a late season red, you probably need to use the other formulation, which is Ridomil + copper. Both Ridomil and phosphite are good with kick-back, but you probably want to add a protective material to cover both directions. Examples would be captan (FRAC = M4), or ziram (FRAC = M3), or Revus, Forum (FRAC=40), or Zampro (FRAC=40+45), or Ranman (FRAC = 21)). Please note that Revus, Forum, and Zampro all have the same mode of action (i.e., you cannot rotate among these three.) Also, copper materials (FRAC=M1) works well against downy mildew. If you decide to use a copper, my current preference is one of newer materials (e.g., Cueva, Badge, etc.), which have a lower copper concentration (but still works well).

As Tony indicated in his newsletter, keep eye on the concentration of the phosphite material. If you exceed the amount, it may end up with phytotoxicity.

Many people have asked me about the combination of copper and phosphite. I have heard that there is a pre-mixed product of copper and phosphite sold in Europe, so, these compounds can be mixed. However, both products are sensitive to water pH. It needs more research, but I have a feeling if you miss the sweet spot on the pH, it can cause toxicity on vines. So, if you wish to try, my recommendation is to make sure you have a good pH (close to the neutral), and try it on a small block of your vineyard (or even a few vines). Also, I wonder about different copper formulations (sounds like a good summer project for us. we will see...)


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