Saturday, May 18, 2019

At bloom Botrytis and ripe rot management tips

This is the second part of "at bloom" fungal disease management tips. Please refer to yesterday's post as well.

The spray timings for Botrytis is at bloom, bunch closure, and veraison.  The pathogen has a wide host range and seems to be active throughout the season, but blooming time is considered as a critical timing because the pathogen can infect flowers without showing symptoms.

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 a very important aspect of 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), Miravis Prime (7+12)*.

The material with an asterisk has a high concern for resistance development. Please note that group 7 is considered a high-risk material. Dr. Baudoin's lab has identified strong evidence of resistance against Endura and Pristine. For the other group 7 materials, such as Kenja, Luna, and Miravis, the way they work is the same as the other group 7 materials; however, 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. Thus, it may take a while for our Botrytis isolates to find a way to overcome these materials. However, cases of fungicide resistance for these newer materials are reported in other crops or in lab studies. Thus, I would be very careful about 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 to lower the risk of fungicide resistance development.  If you think one of the 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 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 to manage 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.

Both ripe rot and bitter rot are considered as 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 round dark brown lesions 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 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), azoxystrobin (FRAC=11), and Swith (FRAC=9+12) provided some level of efficacy against ripe rot pathogens; however, none of the products provided sufficient degree of control by itself. Also, some of the 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 the application will be similar to that of Botrytis: bloom, bunch closure, and veraison.

Friday, May 17, 2019

At bloom disease management tips

Many people in northern VA are about to see blooms in a few weeks, and I am sure the rest of the regions are about to see bloom very soon.  Bloom is a start of 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.

What I recommend often is the 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 (= FRAC) groups.

Since we have experienced rain every weekend (and looks like another rainy weekend coming up), we need to be on top of downy mildew and black rot management. In our vineyards, I noticed that there were several leaves with small lesions of downy mildew.

Protective materials for downy mildew are: Mancozeb (FRAC=M3) [Gavel has mancozeb + zoxamid (FRAC=22)], Captan (FRAC=M4), Fixed copper (FRAC=M1), Revus or Forum (FRAC=40), or Zampro (FRAC = 40+45), or Ranman (FRAC=21)).  (Please note that there is an increasing case of Revus resistant downy mildew isolates in VA. Plus, resistance to Ranman is known among downy mildew pathogens of other crops. Make sure to spray before the rain and rotate!)

Protective materials for black rot are: Mancozeb, QoI (FRAC=11, Aboud, Flint, Pristine, Intuity, etc.), and DMI (FRAC=3, tebuconazole, Elite, Rally, etc). Captan and copper won't work against black rot.

We do have materials with kick-back activities against downy (Ridomil products (FRAC=4), phosphite (FRAC=P07, Prophyt, Phostrol, etc.) and black rot (myclobutanil (FRAC=3, DMI), etc.),. However, they can be effective between infection and establishment of the pathogen (i.e., the day of rain and 3-4 days after). We do not have any eradicant that can kill already established pathogens. Infection on flowers and young fruits can happen very fast. Unless we have a very dry season (which is a rather rare event), this is the time where you have to be proactive. Thus, please protect your vines. Do not wait until you see diseases!

Also please note that recent warm and humid nighttime conditions are favoring spore production of downy mildew pathogen. For example, since 5/1, there were six days with RH near 90% and the temperature was in the 60’s. It is not as threating as in 2018, where at this time of the season, we already had several days of RH > 90% and temperature > 70F, but we still need to be on alert.

In addition to downy and black rot, we need to think of Botrytis, ripe rot, and powdery mildew. (I will cover Botrytis in more details in the next post (probably tomorrow), since this post is getting very long already.)

Here are three examples I thought of considering current conditions.  (Note: I am considering a phosphite (e.g., Prophyt) and Ridomil products, but not listed in the plan.  I will add a phosphite or Ridomil products for downy mildew whenever we have many rain events. Please limit the use of Ridomil products to twice a season for resistance management)

Plan A (my "standard" program)

  • At bloom: mancozeb + sulfur (FRAC=M2) + myclobutanil or another DMI + Vangard (FRAC=9, or other Botrytis material)
  • First cover: mancozeb + sulfur + Quintec (FRAC=13) (or other PM material, such as Vivando (FRAC=50) or Torino (FRAC=U6))
  • Second cover: mancozeb + sulfur + myclobutanil or another DMI
  • 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)

  • At bloom: mancozeb + sulfur + Revus Top (FRAC=40+3) + Vangard (or another Botrytis material) (note: Revus Top contains a DMI, which should provide extra kick against powdery mildew. Also, you can use Gavel for mancozeb to have additional downy mildew material.)
  • First cover: mancozeb + sulfur + Quintec (or other PM material, such as Vivando or Torino) (I may add Ranman to add more protection against downy here)
  • Second cover: mancozeb + sulfur + Revus Top
  • 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)

  • 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))
  • First cover: mancozeb + sulfur + Quintec (or other PM material, such as Vivando or Torino)
  • Second cover: mancozeb + sulfur + myclobutanil or another DMI
  • 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 the bloom, first, and second cover (7 to 12 days), but I may relax a bit for the third and subsequent sprays (10 to 14 days), especially if weather conditions do not favor disease development (i.e., dry).

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 I spray these materials. If you have already used these materials, please rotate with another FRAC group.

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 and copper are 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. A link to 2019 PMG is located on the right-hand menu of this blog (or at the bottom, if you access here with your smartphone or tablet)

Sunday, May 5, 2019

Early season fungicide application reminders

It has been another rainy weekend (1.5 inches so far and still counting), and looks like next weekend will be wet again... Hopefully, this year won't as wet as the 2018 season...

Hopefully, you can provide good protection before the rain, but even if you did, rain more than 1-2 inches can wash the material away from the canopy. Dr. Annemiek Schilder at Michigan State University has a great article 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.
Downy mildew symptoms on the upper leaf surface

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 (e.g., 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 and you were not able to cover before 1-2 inches of rain), it is probably a good idea to have a phosphite material (FRAC = P07) 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)).  (Please note that there is an increasing case of Revus resistant downy mildew isolates in VA. Make sure to spray before the rain!)

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. There is a 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.

Ridomil products (FRAC = 4 + M3 (MZ) or + M1(Copper)) 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. Thus, Ridomil products could be a good option if you are concerned about a lack of coverage, and you want to have a very good material to stop the on-going infection. 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 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.

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 rain event(s). In such a case, a copper (FRAC = M1) material might be a good fit. It is more economical than other materials, has 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). Another option is captan (FRAC = M4). Both copper and captan material are 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.

One of the reasons why I mention about copper and captan is because of the use limitation of mancozeb. In addition to the well-known 66-day PHI, there is a limitation in the amount of mancozeb can be used for each year, which is about 19 lb per acre per year. (Please refer to the label for the specific number for your product.)

Lastly, just because we have many rains, it won't stop powdery mildew. Make sure to have a powdery mildew material (sulfur, FRAC = M2, or others) in your tank-mix.