Sunday, May 27, 2018

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.


Thursday, May 17, 2018

More about options for current rainy situation

I have added more information to the yesterday's post. Please check it out.

Options against current rainy condition.

Wednesday, May 16, 2018

Rain rain rain... What should we do?

As if almost a week of thunderstorms and rains was not enough, it looks like we are expecting even more rain in the coming week.

Hopefully, you had a good protection before the rain, but even if you did, rain more than 1-2 inches can wash the material away from the canopy. Please see the article from Dr. Annemiek Schilder about rain and wash off of fungicide. Her work suggests that although only a 0.04 inch of rain can wash a certain percentage of a material from the leaf, it takes about 1-2 inches to actually having a negative effect on the efficacy since the rate you apply is typically much higher than the threshold for the efficacy of the material.

When we have the next chance of application, what material(s) should we apply? I think many of us are about 2-4 weeks away from the bloom, so, the major concern is downy mildew. If you think you have missed the window (i.e., there were more than 2 inches of rain from the last application of a fungicide against downy mildew, or it has been more than 10 days from the previous application), it is probably a good idea to have a phosphite material (FRAC = 33) such as Prophyt, Phostrol, etc. It has a kickback activity against downy mildew (i.e., it can stop the ongoing infection process). While you are at it, it probably a good idea to mix with a protective material (e.g., captan (FRAC = M4), or mancozeb, ziram (FRAC = M3), or Revus, Forum (FRAC=40), or Zampro (FRAC=40+45), or Ranman (FRAC = 21)). If your vines are within two weeks of bloom, it is probably better to include mancozeb plus a QoI (FRAC=11, e.g. Abound, Flint, etc) or a DMI (FRAC=3, e.g., Rally, Mettle, etc) for black rot.

The other potential scenario is that you have applied materials just before the recent rain events, so, you might not be too concerned about the missing window, but you want to have an insurance against the upcoming week of rain. If that fits, a copper (FRAC=M1) material might be a good fit. It is more economical than other materials, has a good efficacy against downy mildew, and it tends to do better under frequent rain condition. There are several newer copper materials that cause fewer phytotoxicity issues even on relatively copper sensitive cultivars (e.g., Cueva, Champ, etc). The copper material is not effective against black rot, so, if your vines are near bloom, make sure to have mancozeb plus a QoI or a DMI for black rot.

(Addendum 17 May 2018) I received an email about the use of Ridomil products (FRAC = 4 + M3 (MZ) or + M1(Copper)), which have excellent kick-back activity against downy mildew. Typically, I recommend the use of phosphite as noted above because Ridomil products have known fungicide resistance issue. However, with the current rain situation (plus more on the forecast), Ridomil products could be a good option too. Please make sure not to spray too many times. Although you could apply up to four times according to the label, my recommendation is to limit the use of it to twice a season. We have too many fungicide resistance issues in our state, and and the overuse (and misuse) of a product is the most likely cause. Also, although Ridomil MZ has mancozeb, the concentration of mancozeb will be less than our typical recommendation (3 lb/A). You may want to adjust it by adding mancozeb (to meet 3 lb/A) or other a material(s) to cover black rot.

Another question came to my attention was about the difference between the QoI and DMI in regards to their kickback activity against black rot. In between them, the DMI is known to have a better (i.e., reach out longer) kickback activity than the QoI. So if you are in doubt about black rot, a DMI maybe a better option (but also think about powdery mildew. With this rain, I am not too concerned about powdery now, but you may need to keep the DMI for powdery too.)

Friday, May 4, 2018

Bud break and rain...


Bud break for our younger (2-3 years old) Chardonnay happened around 4/20/2018, and for older Chardonnay, it was the last weekend, (4/27/2018). Looks like we are about 1-2 weeks behind of a "typical" spring.

But as with a typical spring, rain comes when grapes break buds! Looks like we will see some precipitations this weekend. Please make sure to have a good protection against Phomopsis as we discussed in the previous post. 

Let's hope that our season will be as good as 2017.