Many people in northern VA are about to see blooms (our Chardonnay vines are trace bloom as of June 2nd, the one on the picture is one of the few with many open flowers), and I am sure rest of regions are going through bloom by now. Therefore, many of us are in the critical time for cluster infections by downy mildew, powdery mildew, and black rot. Bloom time is also critical period to prevent Botrytis, ripe rot and Bitter rot, because pathogens of these diseases can infect flower parts and come back later.
We do have materials with kick-back activities against downy (Ridomil products, Phosphonates, etc.) and black rot (myclobutanil, etc.), but infection on flowers and young fruits can happen very fast. Unless we have a very dry season, this is the time where you have to be proactive. Thus, what I recommend often is use of protectant materials to protect tissues for 4-6 weeks for V. vinifera varieties, and 3-4 weeks for V. labrusca varieties, which should translate into 3-4 sprays for vinifera, and 2-3 sprays for labrusca. Please make sure to rotate mode of action groups.
Here is an example from our experimental vineyards.
1) At bloom: mancozeb + sulfur + myclobutanil or another DMI + Vangard (+ phosphonate, if it rains a lot)
2) First cover: mancozeb + sulfur + Quintec (+ phosohonate, if it rains a lot)
3) Second cover: mancozeb + sulfur + myclobutanil or another DMI (+ phosohonate, if it rains a lot)
4) Third cover: captan + sulfur + Quintec (if needed, if I do not see any evidence of powdery mildew, I may omit Quintec from this spray) (+ phosohonate, if it rains a lot)
The spray interval depends on the weather conditions; so, I cannot give you a specific number. However, in general, I would aim for shorter intervals for sprays #1, #2, and #3 (7 to 12 days), but I may relax a bit for #3 and #4 (10 to 14 days), if weather condition does not favor downy or black rot.
- I am saving my DMI (Rally, Elite, Mettle, Revus Top, Luna Experience, etc, etc.) and Quintec (or Vivando, Torino, or any other new powdery material) usages for the critical period, thus this is the only time we spray these materials.
- I would like to use a mancozeb product around bloom because it has activities against multiple pathogens including pathogens for black rot and ripe rot.
- Captan is not as effective as mancozeb when it comes to black rot management.
- The third cover may become too close to the 66-day PHI, so, you need to be careful with the usage of a mancozeb product.
Of course the example given above is just one example, and there are many other options. For example, there are many new materials became available for powdery mildew management in recent years. Thus, as usual, please refer to our PMG for more details.