Thursday, May 28, 2015

Bloom time fungicide considerations

The warm 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 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.  (Note: recent warm and humid night time conditions are favoring spore production of downy mildew pathogen)  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 V. vinifera, and 2-3 sprays for V. labrusca.  If you have hybirds, 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 from our experimental vineyards.  (Note:  I will add a Phosphonate product for downy mildew whenever we have many rains)

Plan A (my "standard" program)
  1. At bloom: mancozeb + sulfur + myclobutanil or another DMI + Vangard
  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) 
 Plan B (if your major concern is downy mildew)
  1. At bloom: mancozeb + sulfur + Revus Top + Vangard (or another Botrytis material) (Revus Top contains a DMI)
  2. First cover: mancozeb + sulfur + Quintec (or other PM material, such as Vivando or Torino)
  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)
  1. At bloom: mancozeb + sulfur + Luna Experience  (Luna Experience contains a DMI)
  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 am 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 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.

Thursday, May 21, 2015

More on fungicide (re)application timing topic

I posted general "rule of thumb" about application (or re-application) earlier this season.  Dr. Annemiek Schilder at Michigan State University recently published a very nice write up about it.

She answers many of questions we have in our mind, when the fungicide residues to be washed off from the rain, efficacy of spreader-stickers, and systemic fungicides.  Please check it out.

Monday, May 18, 2015

Mealybugs are on its move too!





Today is the one of the days when you find many things in the vineyard!  Mealybugs (white one in the middle of the picture) are also observed, mainly at the base of the shoot (or a spur in this case).  You also see a scale insect on this picture.  Please note that both mealybugs and scale insects can transmit several virus pathogens, including the ones cause grapevine leafroll disease.   Unfortunately, once the vine is infected, only remedy is removal of the infected vine.  (However, please note that the presence of leaf roll virus does not always results in immediate loss of crop.) 

If you have both mealybugs and virus infected vines, and have a plan of expansion, it is probably a good idea to protect new vines using insecticides.  However, you have to make sure you have both the virus and mealybugs to justify your action since insecticides for mealybugs are relatively expensive, and as with other chemicals, application of unnecessary insecticide is not recommended.  If it is not properly applied, that extra application of insecticides may results in the outbreak of other insect pests or development of insecticide resistance.

If you are aware of mealybugs, or having a suspicious vines, it is best to submit samples to one of the labs that test vines of viruses. 



* Eurofins STA Laboratories in Gilroy, CA
(http://www.eurofinsus.com/stalabs/products-services-grapevine-testing.html).  The contact person is Judit Monis (phone: 408-846-9964; email:juditmonis@eurofinsus.com)
* AL&L Crop Solutions, in Davis, CA
(http://www.allcropsolutions.com/diseasetesting/).  The contact person is Anna-Liisa Fabritius (phone: 530- 759-9460; email: info@allcropsolutions.com)
* Agri-Analysis, W. Sacramento, CA. (http://www.agri-analysis.com/).  The contact person is Alan Wei 800-506-9852, email info@agri-analysis.com

Updates on the previous post (Downy mildew)

On the previous post, I mentioned that "At this time of the season, what we typically recommend is either mancozeb or captan mixed with sulfur to protect young shoots and leaves.  The reason why I typically do not recommend a use of newer materials such as Revus or Phosphite for downy or Luna or Rally for powdery is because we want to keep it for the critical time for cluster infection, which is from bloom to 4-5 weeks after bloom."

However, it looks like at out site, the downy mildew pathogen is taking advantage of the weather conditions.  Although our last application of mancozeb and sulfur was only 6 days ago, I noticed that some of older leaves show symptoms of downy mildew (i.e., the infection might have happened prior to the previous application).  At this point, many of leaves look like the first picture, and disease incidence is probably less than 0.5%, thus, it is difficult to find them; however, we came across with a few leaves with clear symptoms as in the second picture.



Thus, I will probably add a phosphite material (Prophyt, Phostrol, etc.) to next round of fungicide application in this week to stop further spread of the disease.  Based on the look on the clusters and warm weather in the forecast, we are speculating that bloom for our Chardonnay will happen in 10-14 days from now.

Warm and wet weekend

Winchester area received a series of rain over the weekend, and it looks like we may see more coming in the next few days.  There were three days of low and moderate Phomopsis infection risk events over the weekend.  Also, humid and warm nights can promote development of downy mildew spores. 

At this time of the season, what we typically recommend is either mancozeb or captan mixed with sulfur to protect young shoots and leaves.  The reason why I typically do not recommend a use of newer materials such as Revus or Phosphite for downy or Luna or Rally for powdery is because we want to keep it for the critical time for cluster infection, which is from bloom to 4-5 weeks after bloom.  If this warm temperature continues, the bloom may comes soon, though!!

Thursday, May 7, 2015

Low Phomopsis risk

Two days of intermittent rain brought a low infection risk event for Phomopsis.  Also, these spring rain events can be precursor events for both downy and powdery mildew.  As noted in the previous posts, keep protecting young shoots from these pathogens.  At this point, you can use mancozeb, captan, and sulfur.

(Note: for some reason, this post was not posted in a timely manner.  Sorry!)

Friday, May 1, 2015

On-going disase risk

As usual, we start our season with rains.  It has been more than 13hr of wetness so far at Winchester with an average temperature of low 50s.  It has accounted for a low risk of Phomopsis infection, and a line of rain just passed the area too.  We will see how it will turn out over the weekend.

As shoots extend rapidly in the early part of the season, the new tissues are not protected by the previous application of fungicide(s).  Keep in your mind to protect these new tissues.

I often am asked about when to reapply fungicide(s) after rain.  An often discussed rule of thumb is:
  1. < 1 inches of rain: Continue with intended spray interval
  2. 1-2 inches of rain: Consider shortening your spray interval in half.  (E.g., if there is 7 days remaining for the normal spray interval, shorten it to 3-4 days)
  3. >2 inches of rain: Consider re-application soon.
However, please note that it also depends on the history of your vineyard(s), cultural practice, and also cultivar selection too.  For example, if you have not seen downy mildew in the past 4-5 years, have a nicely kept canopies for air movement, and you have relatively downy mildew resistant hybrids, say, Chambourcin or Norton, you may have less issue with downy mildew even if the fungicide coverage is not perfect.