Wednesday, July 18, 2018

Handouts from today's sprayer workshop

Thanks again for coming to today's vineyard meeting. I learned quite a bit!

Here are my handouts (sorry for not bringing enough today!!)

1) Sprayer calibration handout (will open a PDF file)
2) Sprayer calibration aid (spreadsheet)
(In order to use it, please download onto your computer [File -> Download as...])
3) Seasonal grape disease reminder (will open a PDF file)

Sunday, July 8, 2018

Mid-season grape diease management reminders

Most of us are about to finish the critical time when clusters are susceptible to infection by downy mildew, powdery mildew, and black rot.  This critical time varies by varieties, but in general, 4 to 6 weeks and 3-4 weeks from bloom for V. vinifera and V. labrusca species, respectively.  After this critical period, you should be able to relax a bit because these pathogens no longer able to cause disease on berries.

So, what’s next?  As usual, disease dynamics really depends on environmental conditions, cultivars grown, and cultural practice, but in general, this is the moment when you will be thinking about late-season diseases such as Botrytis, ripe rot, bitter rot, and sour rot. 
The spray timings for Botrytis is at bloom, bunch closure, and veraison.  The pathogen seems to be active throughout the season. The main reason we recommend the application of a Botrytis specific material at bunch closure is that this most likely to be the last opportunity for you to deliver the material into the clusters, especially if you grow tight cluster cultivars, such as Chardonnay. 

Also, please keep in your mind that Botrytis is very well known for its capacity to overcome fungicides.  Thus, a rotation of mode of action groups is very important aspect for Botrytis management. Mode of action for a particular fungicide can be found as a FRAC code, which you should be able to locate on the label.  Here’s a short list of materials for Botrytis and their FRAC code in parenthesis: Elevate (17), Scala (9), Vangard (9), Switch (9+12), Inspire Super (9+3), Luna Experience (7+3), Kenja (7), Meteor/Rovral (2), Endura* (7), Pristine* (7+11). 

The material with an asterisk has a high concern on resistance development. Please note that the group 7 is considered a high risk, but I did not put an asterisk on Luna and Kenja. I am not indicating that they are not high risk materials at this point. Although the way they work is the same as other group 7 materials, chemical companies engineered these materials to be delivered into the pathogen differently, so that these newer materials are different in terms of how the fungicide resistance develops. However, cases of fungicide resistance for these newer materials are reported in other crops or in lab studies. Thus, I would be very careful on the usage. [Also please note that Aprovia is also a group 7 material, but it does not have a label for Botrytis.]

When you are not sure how to rotate fungicides, please rotate the FRAC code because two different fungicides with two different chemical names may have the same FRAC code as you see on the list above. Also, tank-mixing with other material, such as captan, which has weak to fair activity against Botrytis, will help lowering the risk of fungicide resistance development.  If you think one of fungicides you are using is not providing sufficient control, please contact Dr. Baudoin or me.

Another management tip for Botrytis is about wounding on berries. Although Botrytis is capable of causing disease by penetrating grape’s fruit skin tissues, it prefers going after wounds. Also, at bloom infection by Botrytis tends to develop into disease when grape fruit skin is damaged, but when the skin is intact, the risk of disease development will be much lower, according to the study done by a Penn State group. Thus, management of the source of wounds such as insects (esp. grape berry moth), or birds, or powdery mildew at early in the season, can help managing Botrytis. Moreover, sour rot pathogens also really like going after wounds; so, the same wound management would be the key for the sour rot management as well.

Speaking of sour rot, a study from Cornell University reported up to 80% reduction of sour rot when they use a tank mix of the insecticide zeta-cypermethrin (Mustang MAX) and the antimicrobial hydrogen dioxide (OxiDate 2.0) weekly starting prior to the appearance of sour rot symptoms (~ veraison). You may not need to spray weekly, but if your cultivar is prone to sour rot, the fruit fly management before symptom development will be the key. Switch also list sour rot (suppression only).

Both ripe rot and bitter rot are considered as a warm season diseases, and in fact, people in the south tend to suffer more from these diseases; however, we can find ripe rot in Northern VA year after year.  In addition, I have heard from growers from PA and MD that they are having issues with ripe rot as well.   

Unfortunately, ripe rot in particular, has been misdiagnosed more than other rots.It shows up as if the berries are sunburned, thus you will see a round dark brown lesion on the top portion of an infected berry. The difference from sunburn is that with ripe rot, there would be the tiny dots you will see within the lesion, which are fruiting bodies of the pathogen. As the time progresses, the lesion expand into the whole berry, and infected fruits become shriveled raisin-like fruits (please see the picture above). With a severe infection, you may see the majority of berries on a cluster shriveled down. Unlike sunburn, it does change the taste of the fruit and wine. Unfortunately, the change is in the negative direction, and a study showed that a consumer panel could detect only 3% contamination in the mast.

Both ripe rot and bitter rot seem to be able to infect berries from time of flowering to the harvest.  Thus, protection is important, especially if you have experienced issues with these diseases in the past. Mancozeb, ziram (FRAC=M3), captan (FRAC=M4), and QoI (Strobirulin, FRAC=11) fungicides are currently recommended. But due to the 66-day PHI of mancozeb, you may not have enough days remained to spray mancozeb at this time of the season. Based on our lab and field tests, mancozeb, captan, copper (FRAC=M1), tebuconazole (FRAC=3) and azoxystrobin (FRAC=11) provided some level of efficacy against ripe rot pathogens; however, none of products provided sufficient level of control by itself. Also, some of isolates causing ripe rot are not sensitive to some of those materials. Thus, when it comes to ripe rot managenent, please think of not only a rotaion of modes of action, but also a tank mix of at least two modes of action. The timing of application will be similar to that of Botrytis: bloom, bunch closure, and veraison.

Monday, June 18, 2018

Handout and slides from recent meetings

Here are my presentation materials from recent meetings. It will open a new window with a PDF file.

1) Slides from beginner's workshop on 6 June 2018.
2) Handout from the VVA summer technical meeting on 12 June 2018

Upcoming vineyard meeting at Rivah Vineyard

There will be a meeting in the 23rd of June (Sat) at Rivah Vineyards at The Grove, Kinsale, Virginia. The meeting starts at 6:30 PM. If you are in the Northern neck or surrounding area, please join us.

Tuesday, June 12, 2018

Location for tomorrow's VVA Summer Meeting

A few people asked me about the specific location for tomorrow's VVA summer technical meeting. The meeting will be held at Brown Bear vineyards (Formally Spring Hills), and the nearest address is: 229 Spring House Lane, Woodstock VA 22664.

Tremain prepared a set of screenshots to help you get there. (Click the images to expand)

Spring House Lane is off from Alonzaville Rd.
Your GPS may overshoot. When you see the vineyard in front of you, you should see the farm road on your right to get to the garage/barn.

See you tomorrow!

Wednesday, June 6, 2018

Don't forget about powdery mildew!

Powdery mildew colonies at the center of two leaves in the picture

With this wet season, what we think most are downy mildew, black rot, Phomopsis, and Botrytis. Powdery mildew is often associated with a dry season, partially because this pathogen does not require rain for its infection process.

However, what they also like to do is grow on shaded leave because they are sensitive to the UV radiation. With very clouded canopy from strong growth triggered from heavy water input (= rain), there are lots of leaves shaded by other leaves. Well, at least that is true in my vineyards... Sure enough, when I took a look at these leaves, I found powdery mildew colonies. 

You can see a small white fuzz (= powdery mildew colony) on two leaves in the picture above. Note that how the leaves are shaded.

We have a fair number of options for powdery mildew management. Sulfur (FRAC = M2) is an economical option, and there are range of products with different modes of action (= FRAC code).  Examples are: a DMI fungicides (e.g., Rally, Elite, Mettle, Rhyme, etc, FRAC 3), Quintec (FRAC 13), Vivando (FRAC 50), Luna Experience (FRAC 7 + 3), Topguard EQ (FRAC 11 + 3), Aprovia (FRAC 7), Torino (FRAC U6), etc. Please make sure to rotate FRAC codes. Try to limit the use of a particular FRAC code to twice a season with an exception of ones starts from M. Unfortunately, we have widespread of QoI (FRAC 11, e.g., Abound, Flint, etc.) fungicide resistance powdery mildew isolates in VA, so, I would not count on the QoI material for powdery mildew management.


I mentioned about Botrytis in the previous post too, but just an another reminder. Development of Botrytis depends on what type of varieties you grow, as well as your canopy management strategies.  White-fruited varieties with tight cluster architecture tend to be more prone to Botrytis.  I.e., a red-fruited variety with loose clusters probably does not have many issues with Botrytis, especially if the canopy is well maintained. Since Botrytis pathogen likes high humidity, poorly managed canopy that traps humidity will help them to thrive. Bloom time is important for Botrytis management because this fungus can infect flower and flower debris, and come back later when berries are maturing. There is a number of Botrytis materials such as Rovral and Meteor (FRAC 2), Elevate (FRAC 17), Vanguard and Scala (FRAC 9), Luna Experience (FRAC 7+3), Kenja (FRAC 7), Switch (FRAC 9 + 12), etc. As with powdery mildew, QoI fungicides are no longer the best material for us due to the development of QoI-resistant Botrytis isolates throughout VA.

Also I should note that a research from Penn State showed that when Botrytis infect flowers, symptom development requires wounds on the berry skin. One of causes of wounds on grape berry skin is powdery mildew which damages skin cells to cause splitting. Also speaking of which, grape berry moth which also causes wounds on the berry skin tends to show up in the vineyards around this time of the year. Unlike diseases, you can wait until you see webbing on the clusters to make a decision on spraying against grape berry moth. More in formation can be found in Dr. Doug Pfeiffer's web page.

As I noted in the previous post, grape clusters are sensitive to infection by powdery mildew, downy mildew, and black rot infection from bloom to 4-6 weeks after bloom. The length of this critical time depends on cultivar. For example, it should be 3-4 weeks for American grapes (V. labrusca),  5-6 weeks for French grapes (V. vinifera), and somewhere between the two for hybrids. I know spraying vineyards are not a fun activity, but please make sure that you have a good coverage during the critical period. In a typical year, once we pass the Fourth of July weekend, we can relax a bit.

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.