Virginia Grape Disease Updates

I wish you and your family a happy new year!!

Winchester area received much needed rain this morning!  It started around 12:40 AM and lasted until 6AM (0.43 in), then the RH was above 90% until 11AM or so.  Thus it accounted for about 10.5 hours of wetness with an average temperature of 63F.  It is long and warm enough for downy mildew. It is so close to the harvest (we are harvesting Tony's Cabernet Sauvignon this weekend) that you may not think of the disease management.  If you did a good job of maintaining vines clean earlier in the season, you probably do not need to be concerned.  However, if you have issue with downy mildew this year, it is important for you to manage even after harvest.  Your vines need carbohydrate stored in trunks in order to survive the winter.  A severe downy mildew infection can reduce photosynthesis by reducing the leaf area with leaf lesions, and also by defoliating leaves.  Thus, if you know there is downy mildew in your vineyards (it often shows up on young...

I was out to the eastern shore for an extension trip and missed the rain event!  During 8/23-24, Winchester area received around 0.29 inches of rain.  The event started from around 5PM on 23rd and ended around 4:30 AM on 24th.  The RH was above 90% until noon or so.  Thus, this event accounted for 20hr of wet event with an average temperature around 68F.  It was warm and long enough for both downy mildew and Botrytis. So far, no rain is in this weekend's forecast. 

Winchester area received 0.42 inches of rain during August 18-19, resulting in 26 hours at an average of 68F. It was long and warm enough for both downy mildew and Botrytis.  Once again, please scout for downy and powdery just in case. Also, we are expecting more rains during this weekend (30-50%).

Finally!  Winchester area had decent rain events over the weekend.  The rain event started from 7:40PM on Thursday (we missed the one earlier that day, although other northern VA area received thunderstorms), and a series of rain went pass throughout last Friday.  The relative humidity was above 90% until 8:20PM on Friday.  It resulted in almost 25 hours of wet event with an average temperature of ~74F.  It was a long and warm enough for downy mildew and Botrytis.  Then we had several rain events on Saturday and Sunday.  None of them are very long, but long enough for downy mildew to cause infection. Once again, we had a dry summer and the threat from downy mildew may or may not be the primary concern.  But if you still have a few more weeks to go until the harvest, please keep your eyes on younger foliages (typically you find them on the upper part of the canopy) for the sign of downy mildew.  It can go from a trace level to an outbreak in...

Winchester area experienced much needed rain events during last week (8/3 to 8/4 and 8/5).  [note: I'm at a meeting right now and I didn't have a time to update the information before I took off to this meeting.] Light rains went through during evening of 8/3 and then after midnight/early morning (1:20AM) in  (8/4), then a thunderstorm hit in the afternoon.  The first series of rains were short and low in the amount of precipitation, but since it occurred at night, the relative humidity stayed high (>90%) until 9:30 AM or so, resulting in 8 hour of wetness with an average temperature of 78F.  The thunderstorm was not as big as we hoped for (it became more severe and brought more rain after it passed our area), and things dried up within an hour.  The midnight rain event was warm and long enough for Downy mildew and Botrytis development. Then another series of thunderstorm hit our area on 8/5.  As with any thunderstorms, it was sporadic and some area ...

Well, I almost missed it, but we (Winchester area) had a short rain event started from Saturday night around 11:20 PM, lasted until 12:00 AM or so Sunday.  Although it was not a major rain event, it started late at night and the relative humidity was high (>90%) until 8:20AM (=9 hours of wetness event), with an average temperature of around 68F.  Thus, it was warm and long enough for both downy mildew and Botrytis.  Since it has been so dry that it may not have much impact, but it is worth noting. We are expecting some chance of rain (30-40%) from tomorrow to Friday.  I'm not sure how much of these chances become real, but we need some rain... Our meeting is coming this Wednesday!  I hope you can make it.

Boy, it was some strong wind we experienced during a thunderstorm yesterday!  I saw a few trees fell down in the downtown Winchester.  That storm brought about 0.38 inches of water, the rain lasted about 80 min, then everything dried up very quickly.  This rain was a borderline case for downy mildew infection event.  This fungus (or oomycete, if you wan to be precise), can infect grape tissues in 90 min.  At the same time, it has been very dry for us, so, the overall risk may be low.  Even though the critical time has passed for berry infection of downy and powdery mildew, you need to maintain your leaves reasonably healthy for your crop and also for next year (accumulation of carbohydrate to trunks).  Please keep scouting for powdery and downy by checking younger susceptible leaves on the top of canopies. The weather forecast is showing a chance of rain tomorrow and Thursday.  I think we need little more rain for our vines... FYI: I will b...

There is a chance of rain this afternoon (50%).  More importantly, there is a heat advisory issued throughout northern VA.  Dulles airport recorded historical high (99F) yesterday.  Please be careful if you are working outside.  We only received less than one hour of rain during early part of the week.  It was a little sprinkles here and there and not a disease event.  (I was so disappointed that I forgot to post on here.)

There are some chance of rain (30-40%) predicted tomorrow and then Tuesday.  At this point the main concern will be downy mildew on foliages and also late season rots .

Finally, we received a decent amount of precipitation.  Although the central VA received a much needed rain on Monday, Winchester and surrounding area received only about 0.02 inches of rain.  Then on Tuesday, Winchester area received a series of thunderstorms from 5 PM until little after midnight on Wednesday (~ 1 inch).  The relative humidity stayed high (>90%) until 8 AM this morning.  It accounted for an estimated 15 hours of wetness with an average temperature of 77F.  It was long and warm enough for infection process of downy mildew, black rot, Botrytis, and Phomopsis. We are also expecting around 30% chance of rain on both Friday and Saturday.

We received a series of thunderstorms from Friday night to Saturday morning.  At Winchester, the rain started around 8:00 PM Friday night and lasted until around 9:40 AM Saturday morning.  Soon after the last drops of rain, the sun came through the clouds and things were dried up again. Thus, it accounted for about 13:40 hours of wetness with an average temperature of about 75F.  It was warm and long enough for downy mildew, black rot, and Phomopsis. We will have a vineyard meeting tomorrow from 11 AM at Blenheim Vineyards .  If you have a time, please stop by.

There are chance of rain (40-70% across the state) predicted during tonight to Saturday. We really need some rains, so, I'm hoping that we all will get a decent rain.  We will see... Now probably many of you are considering disease management at or after veraison.  One of diseases you may be concerned at this time of the season are late season rots (sour rot and/or Botrytis gray mold, caused by Aspergillus niger, Alternaria tenuis, Botrytis cinerea, Cladosporium herbarum, Rhizopus arrhizus, Penicillium sp. , and others).  These late season rots come in when fruit sugar content accumulates around 8%, and often times, white varieties with tight clusters such as Vignoles and Chardonnay, tend to get this disease more than other varieties because of the structure of the cluster which can hold water inside and also because of the fair skin. The sour rot pathogens, including Botrytis, are opportunistic in nature, and the damage and the risk will increase if Botytis rot is in...

As you know, we are expecting to have a high temperature for next few days.  Please protect yourself from heat related illnesses.   Having this much of heat is not really a fun, but there is a good aspect as well.  Powdery mildew pathogen cannot survive very well under high temperature.  At 33C (92F) or more, this fungus will suffer, and colonies can get killed.  If there is an extensive exposure to the sunlight and high temperature (as we have right now), they will have a difficulty surviving.  A study has shown that the fungus colonies will be completely killed after 12 hours at 35C.  Thus, this heat wave should reduce the risk of disease development, especially if you had a good canopy management.

I wish you all a happy 4th of July!! We haven't have rains lately = no risks for downy mildew nor black rot.  If you are happened to be in your vineyards, please scout for powdery mildew. 

Winchester area received precipitations from thunderstorms went through yesterday around noon; however, the rain lasted only 30-40 min and dried up very quickly.  Thus, it was not a significant rain event for any disease development.

We had thunderstorms went though yesterday afternoon in Winchester area.  It started around 2 PM, lasted about 20 min, then another one hit around 3:30 PM to 3:50PM.  However; the air was very dry for last few days, and it seems that leaves dried up very quickly after the storm.  Thus, I think it was not good enough for any pathogens to cause disease. On the other hand, the information is just for our area and your vineyards might have experienced a longer wet event.  Downy mildew pathogen needs only about 90 min to cause infection under the optimal condition (about 68F).  Please check with your local weather service. In addition, if the night time relative humidity is high, say above 85% or so, the condition will favor the pathogen to produce spores.  Based on the weather record, I see such conditions 4-5 days per week on average in the past few weeks.  In the other word, even though we have not received a rain event that can be an infection event...

First time in a few weeks, it has been a weekend with no chance of rain.  But there are some chance of rain (~30%) from Tuesday to Thursday.  We are getting close to the end of the critical time for berry infection by black rot, downy mildew, and powdery mildew, thus please be on top of the situation.

Winchester area received an intermittent rain event from 6:00 AM to 4:00PM yesterday.  The relative humidity stayed high (>90%) until 5:00PM.  Thus, this event accounted for approximately 11 hours of wet event with the average temperature of 74F.  It was long and warm enough for Phomopsis, black rot, and Downy mildew infection event. Thank you very much for those of you who made to yesterday's meeting.  We will have a vineyard meeting tonight at Hiddenbrook Winery from 6:30PM.  Tony and I will be there to discuss about the viticulture and disease management.  If you have a time, please stop by.

Winchester area received a thunderstorm starting around 7:30PM last night.  It lasted only 30 min or so, but the relative humidity stayed high (>90%) until 8:00 AM today.  Thus this event was 12.5 hours of wet event with the average temperature of ~73F.  It was warm and long enough for Phomopsis, black rot, and downy mildew. We will have a vineyard meeting at Rappahannock cellars tomorrow from 11AM.  Also, we will have another meeting at Hiddenbrook Winery from 6:30PM.  Tony and I will be there to discuss about the viticulture and disease management.  If you have a time, please stop by.

If you grow Concord and Noiret grape, please be advised that Revus Top (mandipropamid + difenoconazole from Syngenta) may cause phytotoxicity on these variety. The symptoms are light yellow colored scorched (dead) tissue in interveinal area of leaves, and also some deformation of leaves.  Please check this note from Cornell .  We have been testing Revus Top with our Chardonnay in WInchester for two years, but I have not seen any damages on our vines. We will have a vineyard meeting tomorrow from 11AM at Democracy Vineyards .  If you have time, please stop by.

Winchester area received precipitations from thunderstorms yesterday.  It started around 3:30PM and lasted until 7:00PM.  The actual amount of precipitation was not high (0.05 in) compared with other northern VA regions where a severe thunderstorm warning was issued, but since the ending part of the thunderstorm hit during the evening, the relative humidity was high (>90%) until 2 AM or so.  Thus, it accounted for 11.5 hours of wetness with the average temperature of 73F.  It was warm and long enough for Phomopsis, black rot, and downy mildew. We are still having chances of rain (40-60%) until Monday.

Winchester area received rain from 4:40 AM and a series of rain went through our area until 2:20 PM (0.11 in), the relative humidity was high (>90%) until 4:40 PM, thus, we had about 12 hours of wet event with the average temperature of ~63F.  It was warm and long enough for Phomopsis, Black Rot, and Downy Mildew. We are also expecting more rain during the weekend.  The chance of precipitation (by thunderstorms) is 30-40% throughout the state during Saturday and Sunday.  I think most of us are still in the critical period for berry infection by black rot, downy mildew, and powdery mildew (bloom to 4-5 weeks after bloom).  Please check your spray program and local weather to make an adjustment, if necessary.

It seems like there is a chance of rain starting tonight and all day tomorrow.  I was waiting to see if it changes, but now the chance of rain is near 100% for northern VA, and it is lower for the central and southern VA (about 50%).

Winchester area had thunderstorm yesterday from 12:40 PM to 3 PM (0.27 in), the average temperature was around 72 F.  The relative humidity were low after the storm, thus it accounted for about 3.5 hours of wetness.  Then, another drizzle hit us during 3:20 AM to 4:20 AM (0.02 in), and the RH was high (>90%) until 6:20 AM.  The average temperature during this 3 hour wetness event was 59F.  Since both were relatively short and relatively warm, the risk of downy mildew is the major concern. As I noted yesterday, we are having hot humid early summer which is a conducive condition for powdery mildew.  Here are today's pictures from our untreated vines that started to show the development of powdery mildew (click the picture to see a larger image).  Please scout your vineyards especially the location where leaves are shaded.  Powdery mildew pathogen prefer to thrive under diffused sunlight conditions. This is a close-up of powdery mildew pathogen...

Winchester area received isolated rain events yesterday (6/5/10).  The intensity of the rain varied by area, thus, I'm just giving a general idea.  Based on the record, we had rains between 1-3PM and 7-10PM; however, the events were composed of a series of very light rains (less than 0.01 inches), the relative humidity was low (70-80% range), and temperature was high (mid-80's to mid-70's).  Thus, even though we could have a chance of a long wetness period, my guess is that leaves were not wet long enough for many fungal pathogens (Phomopsis, black rot, and downy mildew) to take advantage.  On the other hand, this humid hot cloudy condition may be ideal for powdery mildew development.   We are still having a chance of rain this afternoon.  It seems like northern VA will receive some thunderstorms.

The situation has not changed yet.  We are still expecting some thunderstorms in the state. The chance of precipitation is somewhere between 30-50% throughout the weekend. Winchester area received about 0.02 inch of rain yesterday afternoon.  It only lasted about 1 hour, thus it was not a critical disease event.  Since most of our berries are still in the critical period for downy mildew, black rot, and powdery mildew.  As I have been discussing in various vineyard meetings, black rot requires a certain length of wetness in order to have an infection.  With the optimal condition (~75F), it requires 6 hours.  Downy mildew takes less, about 90 min.  Powdery mildew does not require rain.  Thus, with thunderstorms, it is important to know how long it lasted.  If it was less than 90 min, you probably do not need to worry about risk of diseases.  If it lasted longer than 90 min, then downy mildew comes into play.  If it started late i...

We did not receive any considerable rain during the weekend.  At this point, I am not certain what to believe.  I think the atmosphere is unstable and conducive to create thunderstorms.  We are expecting 30-40% chance of thunderstorm from tomorrow to Sunday. I have seen a small outbreak of mealybugs in our field (please click the picture to see a larger image).  It is a good news for me because I was looking for them, but as you may know, this insect can vector a virus that can cause grape leaf roll disease.  Thus, if you have seen these bugs, please contact me so that I can visit your place to collect samples.  It is very important for us to know which species are present in VA in order to understand the risk of leaf roll spread.  It is a part of on-going leaf roll project and we need more information on this important pest.  Mealybugs are about less than 1/8 of an inch in length and often covered by white hair-like tissues.  Often time, y...

The previous predicted rain affected sporadically around Winchester area.  The sky was dark, yet no rain at my place, but Winchester airport recorded a light rain for 30 min or so.  Since air was so dry, I think it did not accounted for any disease risks. Now we are expecting to see thunderstorms tonight and tomorrow.  The percentage of precipitation is 50% and 80% for tonight and tomorrow, respectively. 

We had a very warm day that was followed by a severe thunderstorm last night around Winchester.  As with many thunderstorms in the summer (yes, we are still in May...), it was sporadic in terms of the affected area.  For example our station did not receive any precipitation, but my place had about 0.3 inches of rain.  Based on the record from Winchester weather station, the rain lasted about one hour, and the relative humidity was not high, thus, it was not a major disease event.  However, it might have been different at your location.  Please check your local weather station. We are expecting to have another series of thunderstorms in next few days. 

We had some sporadic rain events around Winchester area on 23rd and 24th of May.  Duration of rains during these two days were very short, but the one on 24th was a back to back rain event, and resulted in 2.5 hours of wetness with an average of 66F.  It was long enough for downy mildew. We are also expecting to see more rains later this week, starting tonight.  I understand that right now is very busy for all of us, but please make sure that you are on top of the situation since we are at the critical period for berry infection for downy mildew, powdery mildew, and black rot.

Winchester received a series of rains from 2:20 PM yesterday (5/22/10), and the relative humidity stayed high (>90%) until 9:20 AM.  Thus, we had about 19 hours of wetness with an average temperature of 70F, that accounted for disease risks for black rot, Phomopsis, and downy mildew.  Also, we will have a vineyard meeting at Sans Soucy Vineyards ( www.sanssoucyvineyards.com ) from 11 AM tomorrow.  I hope some of you can make to the meeting.

It looks like the first set of thunderstorm is coming very soon.  (Actually, I see rain drops now.)  I hope it won't stay very long.  There are 30-40% chance of thunderstorm tomorrow too. I received several questions about the risk of downy mildew (DM) based on the previous rain which was a risk event for DM.  Most of questions were about whether to apply a kick-back (curative) activity fungicide such as Ridomil or Prophyt.  At this time of the year, it would be a good idea to consider a kick-back material, if you: 1) did not protect your vines, say, the previous application of DM fungicide was more than 10-14 days ago, 2) had considerable rains since the last application, and 3) had an outbreak of DM in recent years.  In the other words, it is probably not necessary, if you have protected your vines, and/or you haven't have a big out break of downy mildew in recent years.   It will take about 10 days for DM fungus to develop symptoms.  Ple...

(I'm still at a meeting, so, I will make it quick.)  At Winchester, the series of rain started around 2 AM on this Monday (5/17/10), it was not a continuous rain, but we had frequent enough rain events during Monday, Tuesday, and this morning to keep the relative humidity high (>90%) until ~9:30 AM today.  During Tuesday, there was a moment when the RH was little less than 90%, but it was still in high 80's.  Thus, I would say this rain event accounted for about 55.5 hours of wetness and average temperature during this period was about 58F.  Thus, it was long and warm enough for downy mildew, black rot, and Phomopsis.   Some of us are expecting bloom very soon.  Please remember that the critical time for downy, black rot, and powdery mildew berry infection is from bloom to 4-5 weeks after bloom.

I thought the forecast was saying rains from Tuesday, but I guess I didn't read it right.  Now two low pressure systems are coming back to back and we are expecting to see showers during next few days.  I hope you have been protecting your vines since we are getting very close or already at the critical period for berry infection by downy mildew, powdery mildew, and black rot.  If you are at bloom, there are some risk of Botrytis infection as well. We will have a vineyard meeting on 19th at Narmada vineyard.  Since I have an another meeting to attend, Tony will be there to talk about both disease and viticulture tips.  I will ask Kenner to print out my handout for your reference. I will be out of my office due to an USDA-related meeting.  No, it's not one of fun meetings. ;-)  The best way to interact with me for next few days are via email.

At Winchester, the second set of rain started at 4:00 pm on 5/12/10 and then we had several short showers during the night.  In the end, the relative humidity was high (>90%) until 11:00 am on 5/13/10.  The average temperature was 64F, starting with higher temperature (72F) and ended lower (55F).  The total amount of precipitation was 0.08 in. Thus, we had about 18 hours of wet event.  The temperature during 12th was close to the optimal temperature for downy mildew.  As I mentioned in the previous post, we (Winchester) had a potential event for downy on May 3rd, so, I think this rain gave the fungus a good opportunity.  Also, it was high risk event for black rot and Phomopsis. We are expecting to have more rain events during the next week throughout VA.  Plus, I think most of us are expecting bloom very soon.  The period between bloom to 4-5 weeks after bloom is the critical time for berry infection by downy mildew, black rot, and powdery ...

This page from Michigan State University Extension describes the temperature threshold to have frost/cold injury on Concord vines.  Hopefully we won't receive any frost at this point. Also, I updated "labels" on this blog.  Now the name of diseases will corresponds to the entry that is either 1) have a picture or 2) discussed in length.

At Winchester a series of rain started around 11:40 am and lasted until 6:40 pm resulting in 0.1 inches of precipitation.  The average temperature during this period was about 50.5 F.  Since the rain ended late in the evening, relative humidity stayed high (>90%) until 8:40 am today.  Thus, in reality, leaves were probably wet for 21 hours or so, with the average temperature of 55 F. This accounted for moderate risks for both Phomopsis and black rot.  Although there were long enough wet period for downy mildew, the temperature might have been a low side of the activity for the downy mildew fungus, thus, I would rate a low to moderate risk for downy.  Plus we had long enough wet period for the powdery mildew fungus to shoot out ascospores. We had a potential downy mildew infection period back in May 3rd.  This is about the time you will start to see the symptom development (click the picture to see a larger image).  Please check your vines closel...

Some parts of the central and northern VA had a cold morning that may have resulted in frost/freeze injuries on your vines.  You may see younger leaves with damaged tissues that are often become like scorched tissues (lower left leaves on the first picture; click the picture to see a larger picture).  Or you may see entire shoots become wilted (second picture; click to see a larger picture).  If only younger leaves are damaged, the shoots will recover over time. It seems like tomorrow's rain event will be a relatively cold one (mid to low 50's) in terms of the disease development.  Hopefully we don't see a major risk event.  We'll see...

The percentage of the chance are 90% in the northern VA, 80% in the central VA, 60% in the southwestern VA, and 30% in the southeastern VA as of noon today.  Please check your local weather for the details.

Looks like most of us did not receive any precipitation yesterday.  I checked several weather stations around VA.  Some had a trace amount of rain, which probably did not account for any significant disease event.  For conformation, please check your local weather stations. The next rain forecast is on this Tuesday, and it is 60% chance at this point (Sunday).  Tomorrow seems to be less windy than today, so, it maybe a good day for an application, if you needed.

Mmmm...  This will be a tough call.  Northern VA and also Southeastern VA will expect thunderstorms during Saturday morning.  The reasons to justify your protective spray could be: 1) vines has been grown quite a bit over this week due to warm weather; and 2) you might have sprayed more than week or 10 days ago and it is due anyway.  One the other hand, there are reasons to hold off the spray: 1) the expected thunderstorm is in the morning hour and the forecast of Saturday is sunny with high wind, i.e., leaves may not stay wet for a long time; 2) the chance of rain is 30-40% as of this morning; and 3) there are rain forecasted early next week  (20-40% during Tuesday and Wednesday for many parts of VA) and you may want to aim for that rain. Please check your local weather, fungicide record, and disease history of your vineyard to make a decision the best for you.

Thank you very much for those of you came to the vineyard meeting at Horton.  If you could not make to the meeting or could not receive the hand out, please click here to download.

We'll have a central VA vineyard meeting tomorrow at Horton Vineyard from 11AM.  Tony and I will be presenting seasonal reminders on the pest management and viticulture tips.  If you can make it, please join us. By the way, this is a picture of our Chardonnay taken yesterday.  When I checked them on Friday, it was about 5-6 inches growth, but it must have grown 2-4 inches over the weekend.  We are expecting to see some thunderstorm events again during this weekend.  Please keep your eyes on the local weather forecast.

Most of northern VA did not see precipitation until very late last night (~1:30 am).  It seems that the storm system missed most of us, unless you are in West Virginia.  At Winchester location, a series of rain started around 1:20 am, then there were several precipitation intermittently, and it resulted in a total of 0.34 inches of rain.  The relatively humidity was stay high (>90%) until 10:00 am.  Thus, if you count the very first rain, we observed around 8.7 hours of wetness.  The average temperature during this event was around 73F. This was a borderline event for black rot and Phomopsis because they requires about 8 hours at this temperature.  For downy mildew, the temperature range was optimal, thus, the infection risk was probably high.  Also, it was long enough for powdery mildew to discharge ascospores. 

I guess since I wrote about the chance of rain during the weekend, we had a nice sunny Saturday.  The regional radar is showing a strong storm system moving across the Midwest and coming to our direction, but it seems the system is pushed a litte upward than it was predicted in the forecast.  At this point (Sunday noon), there are higher chance (80%) of rain tomorrow (Monday) than today (30%) in northern VA, and the chance of rain decreases somewhat as we go south.  Please check your local weather for more details.

Although the chance of precipitation is between 30-50%, thunderstorms are in the forecast from this weekend to Tuesday for northern and central VA, and during Monday and Tuesday for eastern VA.

There will be an orchard meeting at Winchester AREC on 5/6/10 from 6pm.  The reason I'm posting here is because one of the speakers is Dr. Jeff Derr from Virginia Tech and he will talk about weed management.  If you are interested in, please stop by at our center.

There is another chance of precipitation coming up this weekend.  At northern and central VA, the chance of thunderstorms are 30-40% on both Saturday and Sunday, and at eastern shore, the chance is about 30% on Sunday.  Most of northern VA probably received more than 1 inch of rain during the last series of rain, and depends on how hard it rained, your protection may have been washed out.   A typical rule of thumb for fungicide application timing is "2 weeks or 1 inch of rain whichever comes first", but during the spring when grape shoots grows rapidly, you may need to adjust the schedule based on the growth, thus my recommendation is 7-10 days schedule up to 1 month after bloom, then 14 days. Plus , there is a frost advisory issued for tomorrow morning.  I hope it won't happen...

At Winchester area, the second series of rain started around 5:20 pm on Sunday, then it continued on and off until around 8:30 pm on Monday with about 0.17 inches of precipitation.  Thus, there was about 27 hours of wetness with average temperature of 58F or so.  It was long and warm enough for Phomopsis, and Black Rot to cause infection.  Also, these rains from Saturday probably initiated ascospore release of powdery mildew.  (Powdery mildew does not require water for its infection, but it requires water to release ascopsores from its over-wintering structure.)  The average temperature was low for downy mildew, but between noon to 5 pm Monday, we observed 60-65F while it's raining.  Thus, it might be accounted for downy mildew as well.

The first set of rain (0.11 inches) came around midnight in Winchester area.  It did not last long, but since it came late at night, the relative humidity stayed high (>90%) until 11 am.  Thus, it probably accounted for approximately 11 hours of wetness with an average temperature of around 59F.  Under such condition, both Phomopsis and black rot fungi can cause disease. Then the second set of rain came around 5:20 pm, and this event is still on-going.  I will post the results once it is over.

It seems that we will have a rainy weekend.  Chances of rain are around 40-60% throughout the state.  Forecasted temperature during the hours with a high chance of rain is around mid-50's to low-60's.  This may become our first real risk of disease development.  ( Of course, since I stated that, we may not get rains. ) If you have sprayed in preparation to the previous rains (i.e, within 10 days or so), then your vines are probably protected.  It also depends on how much your vines have been grown and how much rainfall you have received.  At Winchester, many of the rain events were showers with less than 0.02 inches of precipitation, and due to more like a normal weather, shoots were not growing as vigorously as they did few weeks ago.  Please check your record, vines, and local weather history. However, if you were waiting until now and your vines are grown considerably, then you may want to protect your vines, simply because there are three days ...

It seems that the line of rain has passed around Winchester area (Folks around Richmond may see more rain later today).  It started around 7 am and lasted until 11 am or so.  The relative humidity was high (>90%) until 11:40 am.  Thus, this event probably accounted for 4.7 hours of wetness (0.06 inches) and average temperature during the event was 52 F.  It was little too cold and too short for Phomopsis or Black rot to develop.  Please check your local weather for more information.  You can click on the link on the upper right and then type in your zip code to see the record from the nearby weather station.

Throughout the state, there is a chance of rain tomorrow.  In the central and eastern regions it varies from 50-90% chance depends on the location and in which forecast you believe.  It seems the chance is higher around Charlottesville area.  In the northern regions it is around 50%.  Please check your local weather if you need to protect your vines.

I was feeling uncomfortable when the rain came around 6 pm, thinking "it came too early!", there were several rain events last night, but none of the rain did not last very long at Winchester area (< 1 hour around 6 pm, then about 20 min around 8:30pm, and < 1 hour around midnight).  It was so windy that the relative humidity did not stay high, but stayed around 70%. Thus, this series of rain events was not creating a risk of fungal diseases.  I'm more worry about damages done by wind.  I hope your vineyards were OK.

It looks like a line of thunderstorm may pass northern VA tonight.  A chance of rain is 30% during the day and 60% at night.  Since the forecast is a very windy warm night, I am hoping that the rain will dry out soon and won't cause any infection event.

It is sad to share that a tree fruit horticulturist at Winchester AREC, Dr. Rongcai Yuan passed away 4/14/10.  For his obituary, please visit this link .

At Winchester, the rain started around 10:40 am Tuesday, and although it stopped during the night, the relative humidity stayed high (>90%) until 9:20 am today.  During this wet time, the average temperature was around 47F.  This is a borderline case for Phomopsis infection.  If you did not have issues with Phomopsis in the past, the risk was probably close to none.  If you had seem a lots of Phomopsis in recent years, you may have some infection, depends on the temperature you observed during the rain.  If it was mid to low 40's the fungus has a difficulty infecting tissues.  If it is more around 50F, 17 hours of wet period will results in moderate level of infection (15-25% severity with a very strong presence of spores). We (northern VA) may have thunderstorm in this Friday, the rest of the state seems to have several sunny days.  Please check your local weather forecast.

Now it has been changed to 70% chance of rain, starting from 11 am.  Please check your local weather.  The chances of rain in Central and Eastern VA are still in lower percentages.

Those of us in Northern Virginia will have a 40% chance of rain tomorrow (Tuesday, 4/13/10) afternoon.  The temperature expected will be in 50's.  It will take about 7-9 hours for Phomopsis to have an moderate level of infection. Black rot will take about 12-24 hours to infect at that temperature range, so, if it rains and persists, there is a chance for Phomopsis infection.

 It seems that we will observe sunny days with 60-70F for next few days.  Hopefully, the night time temperature won't drop too low.  Our Chardonnay vines are showing a little bit of deformation on leaves, probably due to the low temperature during the night.  Unless we will have more cold nights, it should overcome the stress.  Most of our early varieties (e.g., Chardonnay, Merlot) are in this stage (1-2 inches long).  Please note that the flower cluster is already exposed at this point.  Fortunately, we are not expecting a rain event soon, but at this point, the shoot is susceptible to Phomopsis.  If the fungus successfully infects rachis tissue, it may cause a premature fruit drop later in the season.  The picture on the right was taken last year.  As you can see, a part of rachis became necrotic due to Phomopsis infection, and berries were dropped because the rachis is dead.  The fungus survives in canes and trunks that are ...

We hit 90 F this afternoon.  This warm weather made things go little faster than we would hope.  About 50-60% of our Chardonnay and Merlot are in the stage of bud break, my Cabernet Sauvignon is still holding tight, but I saw Cabernet sauvignon in the other vineyard is about 40-50% bud break stage.  (FYI, last year we hit 50% bud break around 4/25.) Some of us are expecting to see some showers on this Thursday to Friday. It will depend on the history of your vineyard and also the condition of the rain, but if you: 1) experienced severe Phomopsis outbreak in the recent years; 2) see your early varieties are already breaking buds; and 3) are expecting that the rain will sustain for a long time (5-6 hours), then you may need to think about a treatment against Phomopsis. For example, at Winchester, it looks like we have 60% chance of rain from 2 pm Thursday and the temperature is forecasted to be in 70's.  It will be in the same condition until the middle of the ni...

Our Dr. Keith Yoder just announced that he has a new blog about his disease updates on tree fruits .  If you are curious about diseases on apples, pears, and other tree fruits, please take a look at it!

Tony sent out March-April issue of Viticulture Notes yesterday. Along with the newsletter, he sent my fungicide spray guideline for 2010 . If you haven't received it, please let me know so that I can put you on Tony's email list. On that guideline, Ms. Lucie Morton found that I stated the rate of wettable sulfur was 5-10 lb/A and notified me that it should be lower. Although the label allows you to go that high, I agree with Lucie. It really depends on the formulation, so, I cannot give you the exact number for each, but we used Microthiol Disperse at 3-4 lb/A last year and it provided a good control. As I stated at the beginning of the guideline, it is merely a guideline. You need to adjust for your particular situations. Also, please follow the label for the rate, because I cannot cover all possible combinations of chemicals, especially the one with many generics, such as sulfur.

We are having such a nice weather lately. I think most of you are in the field preparing for the up coming season. Our Chardonnay and Cabernet Sauvignon are breeding bleeding now a days. (Typical mistake by a Japanese! I have to blame our education system to mix-up L and R when they taught me.    :p    3/30/10) VCE will be hosting several meetings in the central, northeastern, and eastern regions. Tony sent a notice a few days ago. If you have not received his email, you are probably not on his email list. Please contact him or me so that we can add you on the list. If you are new to the business and/or thinking about establishing a vineyard, please consider coming to our meeting on April 8th. It will be held at our AREC station. We will go over various aspects of viticulture and grape disease management, and it will be aimed at new growers.

I had several inquiries on the pruning wound protection in last few weeks, so, here's some information about it. Pruning wound treatment has been discussed in different places and with different contexts. In California where a disease called Eutypa dieback is a big issue, they tested a wound paste with boron (they called Biopaste), and it seems to protect wounds from the infection. In Australia and New Zealand, they have tested a product called Garrison which seems to work as well. However, these products are not registered, but in VA, Eutypa is not as a big problem as in CA. Thus, I'm not sure they will help us much, even if they are registered. One material that has been registered in VA is Topsin-M. It will be applied as a paint-on ( It is a section 24(c) label for local use in VA. Please see the supplemental label here. ) One of potential advantages of Topsin-M is that the label is also for Botryosphaeria which is very common in VA. If you would like to test this p...

2010 January - February issue of Viticulture Notes is published. There is a section of grape pathology too. Viticulture Notes and other seasonal information is distributed from our viticulturist Dr. Tony Wolf through the email. If you have not been subscribing to Tony's email list, please let me know so that we can add your name to the list. Since out website is in the process of renovation, this issue of Viticulture Notes has not been uploaded yet. In the mean time, I uploaded here for your convenience . I just came back from a meeting in Tennessee where I was invited to give talks about grape disease management ( Tennessee Horticultural Expo ). I had a good time meeting with new people. Tennessee's wine industry is smaller than that of ours, but it's growing strong. I hope we can continue communicating each other because we share similar growing conditions, especially in the southern VA and eastern TN.

VT is working on updating webpages and now our AREC pages has been changed. My new grape pathology page is here (Please click the link). It does not have many information as it did with the previous page, but it will. I will keep this blog because it is more convenient for me. Also, due to the change in URL, many of documents I linked last year is gone. I have restored some of important links, but if the file you are interested in is missing, please let me know.

Dr. Baudoin noticed that there is an error in VT's PMG on the REI for Topsin-M. If you are using Topsin-M, please read the label to confirm the Re-Entry Interval for the formulation. The REI statement for Topsin-M was somewhat confusing. In older labels, the REI was stated as 12 hours in the box of "Agricultural Use Requirements"; however, the list of individual crop stated that for grape was 7 days. The newer label of Topsin-M WSB does not state the REI in the "Agricultural Use Requirements", and now the REI for grape has been changed to 2 days . As usual, please make sure to check and follow the label.

2010 version of Virginia Tech's Pest Management Guide (PMG) is uploaded. There are many useful information on disease, insect, and weed management. Please take a look at it for your reference. As with the last year, I will prepare my version of application guide which focuses on fungal diseases. I'm planning to post it before the VVA winter meeting. If you are non-commercial (i.e., do not have the commercial pesticide applicator license), please refer to the home garden PMG . It shows management methods using non-restricted materials.

I wish you and your family a Happy New Year, and I wish this season to be a good one for everybody. Although not as much as I do during the season, I will update this blog for winter meetings and other information that I think you would be interested in. For a starter, the VVA's Winter Technical Meeting will be held in March 4-6 at Omni Charlottesville. There will be a session for grape trunk diseases that will be served as an update of the summer technical meeting of 2009. Also, I will show some results from my grape leaf roll disease survey and fungicide performance testings. I hope you can join the meeting.