Sunday, April 29, 2012

Disease risks from today's rain

Winchester area received precipitation from around 9:00 PM last night to this morning.  An estimated leaf wetness period was 12 hours with an average temperature of 42F.  Although it was a prolonged wetness period, it did not accounted for disease risks because the observed temperature was too low.

Thursday, April 26, 2012

Early Season Black Rot (revised)

I received three emails from different vineyards (Southern, Northern, and Central VA) with black rot pictures.  Yes, it is a little early for us to talk about black rot, but we had very warm period at the end of March, with rain event (on 24-25th) that are warm and long enough for black rot.  I counted three black rot infection events at our location so far, thus it is not a total surprise to see it.

If you happen to have black rot now, what can you do?  Unlike Phomopsis, black rot pathogen can produce spores after 2 weeks of infection under optimal conditions (> 70F), and if you see the symptoms now, chances are it is ready (or almost ready) for spore production.  Thus, even though we are not in the critical period for berry infection, the spores from this generation will be there for berries.  (yes, it is odd to talk about bloom in the middle of April, but at this rate, it will come soon. Hopefully cooler weather will hold off a bit.  We will see...)

If you only see symptoms on a few vines, then you may ask your crew to go through vineyards (maybe as a part of shoot thinning?) to remove infected shoots and/or leaves and it should reduce the risk of next round of infection.  However, if you have many diseased shoots, this method probably won't work.

If your vines are not close to pre-bloom, you can use mancozeb to provide protection on healthy tissues.  Unfortunately, captan or copper won't provide much efficacy against black rot.  [also, please remember that we do not have any cure for infected tissues, regardless of diseases.]

For pre-bloom or at bloom spray, you can use mancozeb to protect your healthy tissues and add Rally if needed.  Mancozeb will provide a good protection, and Rally will provide a good kick-back activity (i.e., stop on-going infection after rain).  Since Rally is a DMI (or SI) material, I am assuming that other DMI (such as tebuconazole, Mettle, Revus Top, etc) (note: in the earlier post, I was listing other chemicals by mistake, sorry!) does have a similar kick-back, but I do not think we have a good data for it.  (If I can get a culture going, I will start testing on it this summer.)  The other option is a use of QoIs such as Abound, Pristine, and Reason (note: according to Dr. Baudoin, Reason probably won't do much against black rot).  The QoI's are not as good as DMIs in terms of kick back activities, but it should give you a good protection and some kick-back activities.  If you decided to go with a QoI, please mix with mancozeb since QoIs are more prone to resistance development than many other classes of fungicide.

As usual, the decision to mix a DMI or QoI to the mancozeb spray depends on the weather and also what is going on with your vineyard(s).  If you had powdery mildew issues in the past few years, adding a DMI will also benefit to the control of powdery mildew too.  Also, even if you use mancozeb, a rain storm may wash it off from the tissues.  Then a follow-up DMI application may make sense.  On the other hand, if we end up having a very dry period, and you have not have much powdery mildew in the past, the addition of a DMI or QoI won't be needed simply because the black rot fungus requires water to successfully infect grape tissues.  You still need a material for powdery mildew, but sulfur may be sufficient.

Personally, I prefer to see the use of a DMI around bloom for powdery mildew.  It has a good kick-back activity against powdery mildew and black rot, thus, it makes sense to me to use it for this critical period.  For more detailed discussion on the use of these materials, please refer to my workbook, which you should be able to find it on the right-hand side of this blog.

Also, for the future reference, please make sure to remove your infected clusters out from your vineyard.  Dropping them off to the ground won't do much.  Infected clusters will produce black rot spores that are capable of both airborne and rain splash dispersal for the entire season.

Monday, April 23, 2012

Reminder: Vineyard meeting at Barren Ridge

As Tony noted in his email, we will have a vineyard meeting on this Wednesday.
April 25th  Barren Ridge Vineyards,
                  John and Shelby Higgs
                  984 Barren Ridge Rd., Fishersville, VA 22939
                  Start time:  11:00 am at Barren Ridge

Directions: Take Exit 91 off of I-64 (Fishersville). Turn onto Tinkling Spring Road heading towards Fishersville. Turn left on Route 250 West. Just past the Food Lion turn right on Barren Ridge Road and follow for about 3 miles. The winery is on the left.

Topics – Seasonal disease, insect and vineyard management considerations:  Presenters include Drs. Mizuho Nita and Tony Wolf and others to be arranged. We will meet first at Barren Ridge Vineyards and then visit Afton Vineyards (Robbie Corpora managing) and Cardinal Point Vineyards (Tim Gorman).  We should conclude the vineyard visits by 4:00 pm.
Contact: Michael Lachance, VA Cooperative Extension, Nelson County, 434-263-4035

Disease risks from on-goin rain

A series of rain events started around 3:00 PM on 21 April in Winchester area.  We are still receiving some precipitations today, and the relative humidity was high (>90%) all the time.  Thus, so far, we have > 45 h of wetness with an average temperature of 50F.  It has been infection event for Phomopsis and black rot, and potentially for downy mildew.  (The temperature in 22nd and today is low, but when rain started it was in 70's.)  It looks like there are more bands of rain coming in to our area later today.

It has been so dry in our area, so, it was a much needed rain!

Thursday, April 19, 2012

Disease risks from yesterday's rain

Winchester area received a series of rain events from 5:30AM on 18 April.  It lasted about 10 PM.  Since the rain stopped at night, leaf wetness is still on-going (i.e., RH > 90%) as of now (~9AM, makes it 27.5h of estimated leaf wetness), and the average temperature is about 49F.  Thus, it has been an infection event for Phomopsis and black rot. 

Sunday, April 15, 2012

Disease risks from yesterday's rain

There was a very short shower went through Winchester area around midnight last night.  It lasted about 1.5 hrs, the air was relatively dry (~80% RH), and the average temperature was around 53F.  It was too short for disease development.

Tuesday, April 10, 2012

Vineyard meeting tomorrow!

It is just a reminder that we will have a vineyard meeting tomorrow, starting at 11 AM at Horton vineyard and winery, then move to Barboursville.  Tony, Tremain, and I will be discussing about seasonal reminders.

Disease risks from 4/9/12 precipitation

Winchester area received some precipitation last night; however, the length of the rain event was short (30-40 min), the average temperature was low (48-49F), and relative humidity did not stay high due to wind.  Thus, it was not considered as an infection event.  What I observed from the radar was that there are several parcels of rain cloud went through our area, and some of you might have received rain for a longer time period.  Please check your local weather station for more detailed record.

Thursday, April 5, 2012

2012 Fungicide Workbook

Here comes 2012 version of "Workbook for developing an effective fungicide program for Wine grapes in VA" (<- click to download a pdf file).  If you receive Tony's Viticulture Notes, you already have it.

I have been publishing it as a "guideline" in the past, but this year, I decided to format it more like a workbook that helps you plan for the season.  I hope you will find it as a good companion to the PMG (Pest Management Guide from VCE).

I was hoping to get it ready before the season starts, but I missed it by 2 weeks.  Hopefully recent cooler weather holds off disease pathogens!

As noted in the workbook, it is still a work in progress.  If you have any suggestions or comments, please let me know.

I mentioned about uneven development in the last post, but as of this morning, our 4-yr old Chardonnay and Merlot are 100% bud break with some of them are 2-3 inches (4 leaves exposed) stage.  We are also looking for another potential frost event(s) in next two nights.  Hopefully, we will dodge them!

Tuesday, April 3, 2012

Disease risks from 4/2/12 precipitation

Rain from yesterday (4/2/12) started around 9PM on 4/1, and lasted until 2:30AM or so.  The RH was high (>90%) until 3:55AM, thus this was about 7 hours of wetness period with an average temperature of 55F.  That was Phomopsis infection event.

Our 4th year Chardonnay is about 1.5 inch growth (3rd and 4th leaf visible); however, there are noticeable differences among vines.  Some are almost 100% bud break with a significant growth and the others are less than 10% bud break with very minimal growth.