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...)

Tuesday, April 11, 2017

Bud break (for us)!!

It looks like the 2017 season for us has officially begun. Our 8 years old Chardonnay at Virginia Tech's Winchester AREC was about 10% bud break as of yesterday. Despite a warm winter, a colder spring might have kept things slow (I am not complaining!)

Once again, the important disease at this point is Phomopsis cane and leaf spot. Please refer to my previous post about Phomopsis management.

Also for our Chardonnay plot, we have a chronic issue with climbing cutworms. Since we know the location of our vineyard where we always see some damages, we typically apply an insecticide to the panels of vines that is facing a wooded area. Without spraying the whole vineyard, it seems to provide adequate control.

Good luck with the 2017 season. I will post key disease management tips as the season moves along.

Thursday, April 6, 2017

Early season disease reminder: Phomopsis cane and leaf spot

Our Chardonnay and some of the hybrid vines are in bud swell stage as of this week, and others are tagging along.  It looks like we will see bud break very soon with warmer temperature coming up next week.

One of the diseases you need to consider this time of the year is Phomopsis cane and leaf spot.  It causes minor leaf spots, which is more obvious to our eyes, but the more important damage is caused by necrotic lesions on shoots and rachis. It also causes berry rot; however, it is not common with wine grapes because of our spray programs. Materials for black rot and downy mildew are often effective against Phomopsis. Thus, the fungicide coverage for these diseases is also working as management of Phomopsis, especially later in the spring and early summer. Some cultivars, such as Viognier and Seyval Blanc, are more susceptible to Phomopsis than the others.

Phomopsis takes a while to establish in the vineyard. It may take 5-6 years for Phomopsis to become noticeable if you start a new vineyard. However, once established in a vineyard, it is difficult to get rid of this disease. Phomopsis tends to become noticeable as a vineyard gets older because of its life cycle. The fungus survives in canes and trunks that were infected in previous years. During the spring, it will produce spores on the surface of infected tissues, and these spores are splashed by rain onto new shoots or leaves. Luckily, the pathogen (Phomopsis viticola) produces spores mainly during the springtime. Thus, unlike the other diseases we face, there is only one major infection period throughout the season. Because of that, the spread of Phomopsis does not happen rapidly as other grapevine fungal diseases, such as downy mildew. Moreover, Phomopsis spores can cause infection under the relatively cooler environment (the upper 40s). Thus, springtime rain events are ideal for Phomopsis to produce spores and cause infection. Unfortunately, we do not have curative fungicides for Phomopsis management; therefore, it is important to protect young tissues when they come out from the older canes and trunks.
If rain events are coming into the picture after bud break, mancozeb (FRAC=M3, Penncozeb, Dithane, Manzate, etc.), Ziram (FRAC = M3), and captan (FRAC = M4) are effective protective materials against Phomopsis. In a typical year, one or two applications from 1-2 inch shoot growth will be sufficient, because your downy mildew or black rot applications, which happens in the late spring, will cover Phomopsis as I mentioned earlier. QoI, such as Abound and Pristine, as well as SDHI, such as Luna Experience and Aprovia, work too; however, you don't want to use them this early in the season because you will need these materials for the latter part of the season to control other diseases.  Once again, protection is the only mean of chemical management because no materials are effective after the infection.

Wednesday, April 5, 2017

Presentations and handouts from Weekend Warrior IPM workshop

It was very nice to see you all at the Weekend Warrior Grape IPM workshop. I think we had a very good time with lots of discussions. Hopefully to see you at other meetings.

Here is a list of materials that we covered during the meeting.