Bloom time fungicide application suggestions

Although our bud break was about two weeks behind of a typical year, the wet and hot May pushed our vines forward rather quickly.  Many people in northern VA are about to see blooms (our 3-year old young Chardonnay vines are trace bloom), and I am sure rest of regions are going through bloom by now. This means that many of us are in the critical time for cluster infections by downy mildew, powdery mildew, and black rot. Bloom time is also the critical period to prevent Botrytis, ripe rot, and bitter rot, because pathogens of these diseases can infect flower parts and develop symptoms later.

With all the rains we observed, many people are concerned about downy mildew and black rot. In our vineyards, I did not see much sign of downy, but there are many leaves with black rot. It is probably because we did not have major downy mildew outbreaks in past three years.

We do have materials with kick-back activities against downy (Ridomil products (FRAC=4), phosphite (FRAC=33, Prophyt, Phostrol, etc.) and black rot (myclobutanil (FRAC=3, DMI), etc.), but infection on flowers and young fruits can happen very fast. Unless we have a very dry season (and we do have a wet season!), this is the time where you have to be proactive.  Also please note that recent warm and humid nighttime conditions (e.g., when I checked last night, RH was 90% and the temperature was in the 70’s) are favoring spore production of downy mildew pathogen.

What I recommend often is a 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 V. vinifera, and 2-3 sprays for V. labrusca.  If you have hybrids, they are somewhere in between, so, 4-5 weeks to be protected.  As usual, please make sure to rotate mode of action groups.

Here are three examples I thought of considering current conditions.  (Note:  I will add a phosphite product for downy mildew whenever we have many rain events)

Plan A (my "standard" program)

1. At bloom: mancozeb + sulfur (FRAC=M2) + myclobutanil or another DMI + Vangard (FRAC=9, or other Botrytis material)
2. First cover: mancozeb + sulfur + Quintec (FRAC=13) (or other PM material, such as Vivando (FRAC=50) or Torino (FRAC=U6))
3. Second cover: mancozeb + sulfur + myclobutanil or another DMI
4. Third cover: captan (FRAC=M4) + sulfur + Quintec (or other PM material, such as Vivando or Torino) (Note: if I do not see any evidence of powdery mildew, I may omit Quintec from this spray)

Plan B (if your major concern is downy mildew: note: I will add a phosphite or Ridomil product based on rain condition)

1. At bloom: mancozeb + sulfur + Revus Top (FRAC=40+3) + Vangard (or another Botrytis material) (note: Revus Top contains a DMI)
2. First cover: mancozeb + sulfur + Quintec (or other PM material, such as Vivando or Torino) (I may add Ranman (FRAC=21) to add more protection against downy here)
3. Second cover: mancozeb + sulfur + Revus Top
4. Third cover: captan + sulfur + Quintec (or other PM material, such as Vivando or Torino) (Note: if I do not see any evidence of powdery mildew, I may omit Quintec from this spray)

 Plan C (if your major concern is Botrytis and powdery mildew)

1. At bloom: mancozeb + sulfur + Luna Experience (FRAC=7+3, Luna Experience contains a DMI) (Using FRAC=7 will give you an opportunity to use other Botrytis material (say, FRAC=9, 17, etc), if bloom last longer than expected or use these FRAC at the other spray timings (bunch closure and veraison))
2. First cover: mancozeb + sulfur + Quintec (or other PM material, such as Vivando or Torino)
3. Second cover: mancozeb + sulfur + myclobutanil or another DMI
4. Third cover: captan + sulfur + Quintec (or other PM material, such as Vivando or Torino) (Note: if I do not see any evidence of powdery mildew, I may omit Quintec from this spray)

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), especially if weather conditions do not favor downy or black rot.  Please note that I was saving my DMI and Quintec (or Vivando, 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 and critical 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 examples above are just examples, and there are many other options.  For example, there are many materials available for both downy and powdery mildew management in recent years.  Please refer to our PMG for more details. The 2018 PMG can be found on the right-hand menu of this blog.