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.)