Saturday, September 9, 2017

A quick reminder before in-coming rain events

Looks like we will likely to have another round of rain from Hurricane Irma sometimes next week.
Just a reminder that we do not have any curative materials for Botrytis and other late season rots. In order to obtain better results, you need to protect your vines before the rain!

Please see the previous post for disease management tips and the list of low PHI materials for each diseases.

Also, it is very important to keep FRAC codes rotated!

Monday, August 14, 2017

Late season downy mildew management and a list of low PHI materials

At Winchester, night time temperature in recent few days is getting pretty low to the point that relative humidity during the night is close to 100%. In addition, we are looking at a thunderstorm forecast tonight that will bring high relative humidity. These conditions favor downy mildew development because downy mildew pathogen prefers to produce spores under dark, humid conditions.

At this point, you do not need to worry about downy mildew infection on clusters; however, they can still infect leaves. Often time, you will initially see infection on the top of the canopy because younger leaves are more susceptible than older ones. Losing the top leaves and laterals are not a big deal; however, once the infection gets severe, it can defoliate many leaves rather quickly (as in the picture above), and that can affect maturing process.

As usual, it is much better and easier to have a preventative program than trying to play the catch-up game. There are many good protective materials for downy mildew, such as Revus products, Zampro, Forum (Please note that these three share the same mode of action (FRAC=45 40 (My mistake. Thank you for pointing it out!))), and Ranman (FRAC=21). In our small trial, fixed copper (FRAC=M1) worked pretty well against downy mildew when we compared with captan (FRAC=M4). Captan worked too, but a fixed copper product lasted longer than captan. Some wine makers do not like to see captan or copper used late in the season, so, this time of the season maybe the best timing to use copper and captan for downy mildew. You can also use a phosphorous acid product (FRAC=33) as well. For some cultivars, you may still use zirum (FRAC=M3) which has a 21-day PHI. Please mix and match to rotate among mode of action groups.

Downy is not the only disease you need to consider. Especially for folks in the northern VA who has been receiving more rain than the folks in the central VA, the risk of Botrytis outbreak can be high. Typically, I post end-of-the-season application tips in September, but it looks like the season is going much faster than a typical year for some of you. Thus, here is a list of fungicides with relatively low PHI (7 days or less) (a PDF file to download). I cannot cover every single fungicide out there, but I tried to cover common ones. Wine making considerations can influence fungicide uses close to the harvest too. Make sure to communicate with your wine maker(s) if they have a preference on the use of fungicides.

As I noted in the previous post, make sure to rotate mode of action for Botrytis because Botrytis pathogen is known for quickly developing fungicide resistance. I prefer to see a mode of action to be used twice or less per season, especially when we deal with Botrytis (with an exception of fungicides with FRAC code starting with "M"). This is also mentioned in the previous post, but wound management for Botrytis is important. The management of the source of wounds such as insects (esp. grape berry moth), or birds, or powdery mildew at early in the season, can result in the management of Botrytis.  Moreover, sour rot pathogens also going after wounds; so, the same wound management would be the key for the sour rot management as well.

Monday, June 26, 2017

Disease management considerations toward bunch closure

In a typical year, the fourth of July weekend is the time the critical period for cluster infection by downy mildew, powdery mildew, and black rot will end for many of us because it will be about 5-6 weeks after bloom. (Bloom this year was about 1-2 weeks ahead of typical years, so, this week maybe it for 2017.)  This critical time varies by varieties, but in general, 4 to 6 weeks and 3 to 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 are no longer able to cause disease on berries. Plus, powdery mildew tends to slow down because it is not very active under hot condition (> 90F).

So, what’s next?  As usual, disease dynamics depends on environmental conditions, cultivars, and cultural practices you employ, 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 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). 

The material with an asterisk has a high concern for 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 saying that they are not high-risk materials; we simply do not have enough data. However, since they belong to the same mode of action group, I would be very careful on the usage.

When you are in doubt, 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 (M4), which has weak to fair activity against Botrytis, will help 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, according to Penn State’s research, 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.  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 result in the management of 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 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 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 the time of flowering to the harvest.  Thus, protection is important, especially if you have experienced issues with these diseases in the past.  Mancozeb (M3), ziram (M3), captan (M4), and QoI (Strobirulin, FRAC 11) fungicides are currently recommended.  Please rotate among these modes of action because some of the isolates causing ripe rot are not sensitive to some of those materials. Our recent research effort showed that fixed copper materials (M1) have a fair to good efficacy as well, thus, it maybe a good idea to tank mix these materials with a fixed copper. (Note: due to the 66-day PHI of mancozeb, you may not have enough days remained to spray mancozeb at this time of the season.) The timing of applications will be the same as Botrytis, so, include ripe rot material when you apply for Botrytis.

Tuesday, May 23, 2017

Post bloom disease management considerations

As of today, it is about 10% bloom at our Chardonnay plots. Since bud break was about 2 weeks ahead of a typical year, things are moving along as we would expect. Of course, bloom in VA almost always has to happen in rain...

As for bloom time disease management consideration, please refer to the previous post.

From this point on, 4 to 5 weeks will be a critical period for management of downy mildew, powdery mildew, and black rot. Please make sure to keep your vines covered. Once again, providing a protection is much better and easier than playing a catch-up, especially if it comes to grape disease management in VA.

You can use protective materials such as mancozeb, copper, and sulfur as your backbone, and add more specific (and often locally systemic) materials. Some of these materials have efficacy against multiple diseases (either by itself or through the combination of two materials). Examples are

  • DMI, aka SI (FRAC = 3), e.g., Rally, tebuconazole, Mettle, etc. Inspire super is a mixture of difenoconazole (FRAC 3) and cyprodinil (FRAC 9). 
  • QoI (aka strobilurins, Abound, Flint, etc., FRAC = 11), 
  • SDHI (Luna Experience (FRAC 7 + 3), Aprovia and Kenja (FRAC = 7), Pristine (FRAC 7 + 11), etc.) 

Other disease-specific materials include:

  • for Downy mildew: Revus and Forum (FRAC = 40), [note: Revus Top is a mixture of Revus and difenoconazole (FRAC = 3)], Zampro (FRAC 40 + 45), Ranman (FRAC = 21), Phosphites (aka Phos acid, Prophyt, Phostrol, etc., FRAC = 33), etc.
  • for Powdery mildew: Quintec (FRAC = 13), Vivando (FRAC = U8), Torino (FRAC = U6), etc.

Why am I listing all FRAC codes? Because it is very important for you to rotate these FRAC codes to avoid fungicide resistance development. Please do your best to limit the use of a FRAC code (with exceptions of FRAC codes start with M) to 2 times per season. 

Some people prefer to use captan as one of backbone materials. One thing you need to remember is that captan does not have much efficacy against black rot. Thus, if you use captan, you should mix with either FRAC 3 or 11 material for black rot management. Also, please remember that you cannot use captan with an oil because the combination will cause toxicity to grapevines.

Please refer to our pest management guides, which you can find on the right-hand side of this blog under "resources" for more information.

Wednesday, May 17, 2017

Observations from the field

Some shoots of our vines are about to reach the second catch wire, but I saw many that were still about 10-12 inches too. It looks like series of rain during the month of April drove developments of black rot and Phomopsis. Although it was not severe, I found several vines with leaf lesions of black rot, and a few vines with Phomopsis.

Tan-colored lesions are symptoms of black rot. If you click the image, it will open a larger file where you can observe fruiting bodies (tiny black specks) within these lesions.

It is a bit difficult to see, but, please note the holes on the upper picture (in the blue circled area). The lower picture shows more characteristic leaf spots of Phomopsis cane and leaf spot.

For management tips, please refer to my around bloom disease management consideration post. Please remember that clusters will be susceptible to black rot from bloom to 4-5 weeks after bloom. Looks like Winchester area is expecting chances of rain on Friday, Monday, and then Wednesday. As I always mention, it is better and easier to provide protections to your vines before the rain than try to deal with diseases after infection.

Another notable symptom I observed is the one from leaf miner. It is a relatively minor pest of grape, but I often receive questions from growers probably because of its strange mining pattern on the leaf.

For more information, please refer to Dr. Doug Pfeiffer's page.

This is not symptoms, but I also found quite a bit of cicada exoskeletons. Looks like our area (Frederick county) is one of "hot spots" for 2017. Plus, there are reports from northern VA, MD, and DC about the unusual emergence of cicada. Once again, here is a link to Doug's page on the periodical cicada.

Tuesday, May 9, 2017

Bloom time disease management considerations

Many of our vines at VT's AHS AREC are about to reach the first catch wire and going strong. When shoots are about 10-12 inches long, downy mildew, powdery mildew, and black rot tend to show up. Then, at bloom time, flowers and young berries will be susceptible to these diseases until 4-6 weeks after bloom.  In addition, Botrytis, ripe rot, and bitter rot can cause infection on flowers.  Thus, you need to consider multiple diseases management. However, you probably do not need to manage all with expensive materials. What you need to think about is which disease(s) have been the major issues at your vineyards. The disease history of your vineyards tends to repeat itself because of the environmental conditions at your site and availability of spores from previous infections.

Downy and black rot management depend on rains.  I have seen cases where downy or black rot developed before bloom under wet conditions. We receive a little fewer rains than last year, but it is always best to keep up with the protection. If you have concerns on downy or black rot, think about the use of a DMI (tebuconazole, Rally, etc., FRAC 3) or QoI (Abound, Pristine, etc., FRAC 11) material for black rot, and Phosphite (= Phosphorous acid, FRAC 33) or Metalaxyl (Ridomil, FRAC 4) product for downy mildew.  Revus and Forum (FRAC 40), Zampro (FRAC 40 + 45), and Ranman (FRAC 21), can provide a very good protection against downy mildew.

Although it has been relatively cold lately, once we start to see a trend of warm, humid nights, it would be a nice idea to think about downy mildew, since these humid nights can promote spore production of the downy mildew pathogen.  

As for powdery mildew, I prefer to start powdery mildew management (i.e., the use of a DMI or other newer materials such as Quintec (FRAC 13), Vivando (FRAC U8), Luna Experience (FRAC 7 + 3), Aprovia (FRAC 7), etc.) at pre-bloom application in our plots due to heavy powdery mildew pressure at our plots. It seems to reduce the cases of cluster infection for us.  However, please note that in my vineyards, our trials tend not spray as often as many of you do.

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.  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 are a number of Botrytis materials such as Rovral and Meteor (FRAC 2), Elevate (FRAC 17), Vanguard and Scala (FRAC 9), Luna Experience, Kenja (FRAC 7), etc.

Warm weather conditions help the development of ripe rot and bitter rot.  Both of them cause infection from bloom to harvest; however, you do not see actual rots until near harvest.  It is very similar to Botrytis in this regard.  An additional issue here is that both diseases can change the flavor of wine.  If you have seen ripe rot or bitter rot, it would be a nice idea to protect flowers with mancozeb, captan, Ziram, or a QoI.

For Botrytis, ripe rot, and bitter rot, please keep in your mind that early season powdery mildew management can become important to prevent these diseases.  These pathogens are very good at infecting through wounds (plus, the flower infection of Botrytis requires wounds to become rot); thus, scars, which will turn into the opening of the skin, caused by powdery mildew infection on young berries can be the ideal targets for them.

Lastly, please keep in your mind about fungicide resistance issues.  You can locate FRAC code on the fungicide label (or you can take a look at our Pest Management Guide, which you can find on the right-hand side of this blog).  Even if two products are different in names or came from different companies, if they have the same FRAC code, they are basically the same regarding fungicide resistance management.  Please rotate the FRAC code.  For newer materials such as DMI (or SI) or QoI or SDHI, my recommendation is not to repeat the application more than twice, and limit the use of it to no more than three times a season. Less number of application is better for fungicide resistance management. (I.e., Use the same FRAC code only twice (maybe three times) per season, except FRAC codes start with M.)

Monday, April 17, 2017

From bud break to pre-bloom disease considerations

Our reds broke buds, and whites have about 1-inch shoot growth on it today, and more rains in the weather forecast. It is time to think about Phomopsis!

What happen from this point to pre-bloom is a relatively simple spray program to manage Phomopsis, downy mildew, and powdery mildew.

During the early part of the season, I typically recommend a mix of mancozeb and sulfur or copper by itself. The reason why I recommend mancozeb now is because it works on so many different diseases (including Phomopsis which is the main target for us), plus, mancozeb has a 66-day PHI and a limit on the amount of mancozeb to be used in a year (e.g., 24 lb (or 18 lb of a.i) if you Dithane DF). Thus, I would like to use mancozeb-based product early in the season.

I have been often asked whether you should include sulfur or not. If your vineyard has a history of powdery mildew outbreak, it would be a good idea to have a sulfur in your tank mix, even at early part of the season. Although you may not able to see it, powdery mildew pathogen gets active when the temperature gets warmer. It is probably a better idea to have your vine covered than risking.

Some people prefer using JMS Stylet oil for early powdery mildew management. It works, but please keep in your mind that you cannot spray sulfur or captan within two weeks of any oil application. It will cause toxicity to grapevines.

A use of a copper-based product is not a bad idea either. It is relatively cheap and effective against both downy mildew and powdery mildew (but not much against Phomopsis). It may not as effective as mancozeb + sulfur, but it can be sufficient. Also, if you want to keep mancozeb as long as its 66-day PHI and yearly usage limit allows (e.g., you want it for ripe rot management), then copper can be a good rotation partner.

The growth of the shoots during the first several weeks is so rapid that you need to make sure that there is a good coverage before the rain. Please remember that it is much easier and more effective if you protect your vines. Once any of diseases start in your vineyard, a catch-up game tends to be not effective. I have heard from many growers that the number of application tends to be fewer if you are proactive in protecting vines. When you have kept a clean canopy and clusters until the end of the critical times for downy, powdery and black rot (I will cover this topic later), then you can relax your fungicide application program.

(Burning-like symptoms on berries due to fungicide applications after an outbreak of powdery mildew...)