Tuesday, September 29, 2009

Meetings at Koru Farm (Sept 30th) Dinwiddie (Oct 1st) 2009

I think this will be the last meetings for the season.

One is at Koru farm in Stuart, VA (Sept. 30th - TOMORROW!). Caryl and Greg Talcott has been kind enough to host and organize the meeting. If you can make it, please do. I will talk about new fungicide and other management information.

The other one is at Dinwiddie, VA (Oct 1st). Although this is titled late season meeting, I will talk mainly about "early" season disease management for next season, since most of people are probably either harvested, or harvesting their grapes.

The list of speakers (at Dinwiddie):

Dr. Mizuho Nita, VCE Grape Pathologist from Winchester VA, Mizuho will be cover Early Season Management of Grape Diseases.

Dr. Paul Semtner, VCE Entomologist form Blackstone VA, Paul will cover Early Season Insect Control Methods.

Janet Spencer, VCE SE Area Vegetable Extension Agent in Suffolk VA, Janet will cover General Production Tips

Mike Parrish, VCE Extension Agent, Dinwiddie VA, Mike will cover some Pruning Tips for Winter Pruning and Training.

This program will cover information for Both Backyard and Commercial Production.

Directions from Blackstone will be to fallow 460E about 18 miles to Courthouse Rd. Turn Right on Courthouse Rd. and go about ½ mile to Davis Road and turn right. The Coburn’s will be about a ½ on the Right. The Coburns grow 10 different verities of grapes and sells them to Wine Making Hobbyist.

Address is: 15222 Davis Road, Church Road VA,23833

Note: I tried to upload my notes, but VT's server is having an issue. I will do it next week.

Monday, August 31, 2009

Late season management topics

I've been in and out of my office with my leaf roll survey project, and it has been bit difficult to frequently update the blog. Also, at this point, not much you can do about major fungal diseases. The critical time of infection is gone. If you see downy, powdery, or black rot on your bunches, the infection probably took weeks ago, if it was not a month. Thus, I will point some key issues at this time of the year.

Botrytis, downy, and other rot
We had a long period of wet and cool nights during the last half of August. This conditions favors both Botrytis and Downy mildew sporulation, and potential infection on nearby leaves. (i.e., it won't spready quicky, but it probably enough to increase number of spores.) If it is followed by rain (like we had last week), the risks of Botrytis and downy mildew increase. As I mentioned earlier, downy mildew won't touch berries at this point. Berries are resistant to the infection. However, with a prolonged rain or high humidity event, Botrytis can penetrate tissues to cause infection.

As I mentioned in last week's viticulture note, it is good idea to protect your berries with Captan or Captan + Botytis material (Vangard, Elevate, etc), especially when you are expecting rain. Unfortunately, we do not have any curative materials against Botrytis, unless you apply materials within 24 hours, which is not a realistic number. Also, once sugar level go above 20 Brix, nothing much we can do in terms of management.

Downy and Powdery mildews
At this point, your berries are resistant to infection of downy and powdery mildew fungi, thus, your focus will shift to foliage management for both sugar accumulation to berries for harvest and to trunks for winter survival. Typically, foliage is easier to manage than fruit zone and you can extend your spray schedule to 10-14 day interval, especially you do not receive much rain.

Leaf roll survey
As I mentioned earlier, I'm conducting a survey for leaf roll virus (pictured above). Idea here is to have a better picture of leaf roll infestation in the state of Virginia, and also, by monitoring several years, I'd like to know how well it can spread within a vineyard. It is a free diagnostic opportunity for you (funded by the VWB), and there are spots available as of today. If you have any suspicious vines, please let me know so that I can arrange a visit to your vineyards. Other organism that I'm interested in is mealybugs (pictured below). Mealybugs can serve as a vector of leaf roll (virus). As you see in the picture, the bug is very tiny, but you can see them with naked eyes. If you have seen the bug, please let me know as well.

Monday, August 24, 2009

Finally rain has come...

We had fairly dry month so far and grasses are start to getting brown, but a thunderstorm dropped about 0.5 inch of rain last Friday around Winchester area. It stared little after 5:30 pm then continued for two hours or so. The relative humidity was high until next morning (10:30 am) with an average temperature of around 70F. This accounted for infection event for Phomopsis and Botrytis on berries and Downy mildew on leaf.

I listed Phomopsis here simply because it can infect berries at any time; however, often time infection around this time is not common. It is probably due to less inoculum (this fungus mainly creates the fruiting body in the spring), and it favors cooler climate. Thus, your risk depends on how chronically you have Phomopsis in your vineyards. If Phomopsis appears year after year, then your risk is higher. If you just see them only when we have a wet spring as we did this year, you probably have less risk.

As for downy mildew, I started to see foliar symptoms on my sprayed vines here and there. Probablty they have spread using dew periods. Since last week, there were many nights with high relative humidity which promote sporulation of downy mildew, and with a combinaiton of wind and a dew, they can infect some leaves. If day time weather is dry, it is not an issue, but as I mentioned in the last post, you need to protect your foliage to some extent to keep general health of vines. Thus, it is probably a good idea to scout around your vines, and apply curative application if necessary. (i.e., if you have many leaves with downy already, and received as much rain as we did, you probably need some action.) PHI for Ridomil Gold copper and Ridomil Gold MZ is 42 days and 66 days, respectively, and that for Prophyt is 0 day.

Wednesday, August 19, 2009

It was a very nice workshop!

(A graft union infected by fungal organism(s))

We had a very nice workshop this Monday. Now everybody become experts of various trunk diseases! As Philippe discussed, most of fungal pathogens that cause trunk diseases often requires a point of entry. In addition to pruning wounds, accidents with a weed-whacker, etc that were in the discussion, due to cold temperature during winter, some of varieties are more susceptible to have cold injury which also can serve as a point of entry for microorganisms. Site and variety selection can play a big role in prevention of these diseases.

As for other diseases we face, we had several nights with high relative humidity (8/14-16) which favors downy mildew sporulation. Then we had thunderstorm passed by on 17th and 18th. Thus, if you had visible downy mildew colonies on your leaves, the risk of new infection was high during these thunderstorms. (I'm talking about leaf infection, not berries.) At Winchester, last night's thunderstorm did not last very long, but since it came late at night (9:20 pm), leaves were probably wet until 7:40 am or so. This accounts for > 10 hours of wetness, and the risk of Botrytis would be high during this time.

Friday, August 14, 2009

See you on Monday at Jefferson vineyards

We will have Virginia Vineyards Association's summer technical meeting at Jefferson vineyards on August 17th (this Monday). Dr. Philippe Rolshausen and Lucie Morton will be talking about trunk diseases. I will be there to provide some help and learn more about trunk diseases. If you would like to talk to me about other diseases or discuss about your spray programs, please let me know.

Wednesday, August 12, 2009

I'm back!!

Hi all,
I'm back from the meeting. It was a meeting for plant pathologists, and it was a very good meeting for me to meet new people (since I'm a new kid on the block and all), as well as my other colleagues. I visited Washington's Yakima Valley grape growing area after the meeting to visit a collaborator on grape leaf roll disease project. There are very exciting area to study, and I will talk about it more in detail within a few days. The picture was taken from their field and showing mealybug infestation.

In anyway, I took a quick look at what happened (weather-wise) during my trip. It seems like there are very short rains on 7/31, 8/1, and 8/5, and these were not so significant in terms of major fungal disease infection. We had 4.5 hour of wetness on 8/2 which probably accounted for downy mildew infection (primary on leaves, at this point), and 9.5 hours of wetness on 8/6, which probably accounted for downy mildew and Botrytis (and maybe black rot, if your berries are very late and still susceptible). Your berries are probably at or after veraison at this point. I hope you did not forget your protection against Botrytis.

Saturday, August 1, 2009

I'll be out of office until 8/11

I'm at a conference until 8/11. In the mean time, we will have a vineyard meeting at Winchester AREC on 8/5. I cannot attend, of course, but I prepared a note (click here to view) and Tony will go over it.

Since I may not able to update this blog, I summarized the disease risk at this point. I hope it will be helpful.

Disease risks at this point (early August)

The critical period for black rot, powdery mildew, and downy mildew fruit infection should be over (4-5 weeks after bloom).

Black Rot: Berries should not susceptible any longer.
  • For the next year, make sure to remove all berries from your trellis at or after harvest. These infected berries can produce spores all season long if they are left on the trellis
  • Phomopsis: Berries are susceptible all the time.
  • Since we had such a long period of rain in the spring, you may see some berry infections. Usually, the damage done by Phomopsis is not significant, but if you have reasons to be afraid of Phomopsis, captan can be applied to protect berries.
Downy Mildew and Powdery mildew: Berries should not susceptible any longer.
  • At this point, your focus is shifted to management of foliar health for accumulation of sugar to berries (for wine quality) and to trunk (for winter survival)
  • Thus, periodical application of fungicide for downy and powder mildew is necessary; however, you do not need to have an intensive schedule as you may do during the critical time. 10 to 14-day interval should be enough to keep vines healthy unless there are many rain events.
  • Fixed copper is a relatively inexpensive materials that can control both downy and powdery mildew. However, application within 30 days before harvest may decrease the quality of juice for wine making.
  • Other materials to consider, especially within 30 days of harvest, are Potassium salt materials for powdery and Phosphorus acid materials and captan for downy mildew. Pristine can be used up to 14 days prior to harvest too. Please keep your eyes on PHI.
Botrytis: It favors humidity as well: canopy management is important.
  • It is good at take an advantage of wounds. Successful insect management, such as against grape berry moth, helps reduce risk of Botrytis outbreak.
  • There is no formal study done yet, but a combined application of fungicide at just before bunch closing plus at veraison is known to reduce the risk of Botrytis outbreak. Dead grape tissues (flowers, aborted berries) can be a medium for Botrytis, thus, good penetration of spray materials to inside of the bunch is important (an application prior to bunch closing), and the number of Botrytis spores in the air is high around veraison (an application around veraison).
Other late season rot:
  • As with Botrytis, wounded berries can be susceptible to other microorganisms that cause “sour rot” or “bitter rot”.
  • Thus, if you experience damage to berries due to hail, strong thunderstorms, excess moisture etc, you may need to react to the situation. Captan or Captan + Botrytis material is often recommended.
  • When Brix is high (>20 or more), it is very difficult to control growth of microbes.

Other notes about chemical management
  • Mancozeb products (Penncozeb, Dithane, etc) have a 66-day Pre-Harvest Interval.
  • Sulfur applied under high temperature condition (> 85F) can cause damages on vines.
  • Do not mix sulfur (or captan) with oil. It can burn grape tissues. Some insecticide formulations contain oil as a carrier!!

Thursday, July 30, 2009

Rains in the forecast

It seems that we have more rains on the horizon. I hope you had a chance to protect your vines, it it was not done recently. At Winchester area, yesterday's rain events were sporadic and it was not significant disease event except for downy mildew, but some of nearby area probably had more continuous rains, thus you need to check your local weather. We have having 13 consecutive nights that favors downy mildew sporulation, thus even though the threat on fruits are gone, you may want to consider downy mildew materials to protect your foliages.

Monday, July 27, 2009

Many thunderstorms...

We had a series of thunderstorms passed by the area. In terms of the duration of rain, all are short; however, it was wet afterwards because many of these rains happened after 5pm and the relative humidity stayed high until following morning.

On 25th, we had rain started from 9:40 pm and RH was high until 10:00 am next morning (>12 h of wetness). On 26th, the strong thunderstorms passed starting 5:00 pm, and RH was high until 8:00 am this morning (>15 h of wetness). Average temperature during these events were mid-60F, thus, infection of downy mildew, black rot, Phomopsis, and Botrytis could happen. But as I mentioned several times here, if you passed the critical period (4-5 weeks after bloom), your berries should be resistant to downy mildew and black rot infections.

Since we had such a strong wind with the thunderstorms, some of you may have experienced damages on berries (and/or even shoots and trunks). Hopefully they will dried out, but these wounds can be a course of entry for Botrytis and other rotting organisms. This (from bunch close to veraison) is the time for protection against Botrytis nonetheless, so, I would recommend including a Botrytis fungicide in your next application.

Friday, July 24, 2009

Rain after rain....

We had a series of thunder storms on Wednesday and last night. The condition of air were dry to begin with, so, the relative humidity did not stay high after the rains (stayed in 70% range). Thus, these rains probably did not account for disease event at Winchester; however, your vineyard might had more rain or longer rain. Please check your local weather.

Also, we are still having 7 consecutive nights with conditions for downy mildew sporulation. Even with a short rain (>90 min), it can cause an infection, thus, if your berries are still in a critical time (4-5 weeks after bloom), and you see leaves with downy mildew in your vineyards, then you may need to react to these series of infection event with Phosphorus acid or Ridomil products. However, if your berries passed the critical time, the risk of infection is very low.

Once again, the fungus you may need to concern at this point is Botrytis. Make sure to protect your bunches with Botrytis materials (please read previous posts (2-3 post ago) for details).

Wednesday, July 22, 2009

More rains in the forecast

Rain on this Monday did not last long, but since it started later in the day, the relative humidity was high (>90%) until next morning. Thus, we had >15 hours of wetness event with an average temperature of 68F or so. This accounts for infection event for Phomopsis, downy mildew, black rot, and Botrytis, and ascospore discharge for powdery mildew. And I'm aware that areas in the south of us received more rain last night. Please check your local weather record.

In addition, we are having five consecutive nights with high relative humidity that favors downy mildew sporulation. If you have issues with downy mildew this year, you may need to take some action before or after next round of rain. (but again, it depends on growth stage of your berries. If it is past 4-5 weeks after bloom, the risk of downy mildew infection on berries is very low.)

Unfortunately, there is no curative fungicide for Botrytis, thus you need to protect your berries against infection. As I mentioned in the previous post, often time, protection at berry touch and at veraison is recommended. Please refer to either my spray guide or VT's PMG for list of fungicide you can use.

Saturday, July 18, 2009

Two wetness events recorded on Friday

We had two wetness event due to lines of rain passed by yesterday (7/17/09). The first one started around 11:30 am, and wetness lasted until 3:30 pm or so (4 hours) with an average temperature of 71F. The second one started around 8:40 pm and wetness lasted until 2:00 am (6 hours) with an average temperature of 66F. These events accounted for downy mildew infection, potential powdery mildew ascospore discharge, and light infection for Botrytis. Both are little shy for black rot infection event.

As I mentioned in the previous post, your vines should be very close to the end of the critical period. After it is done, you can relax a bit in terms of downy, powdery, and black rot infection on berries.

More rain events are in the forecast on Monday to Wednesday.

Wednesday, July 15, 2009

Rains in the forecast, and a vineyard meeting at Pollak Vineyards

There is a vineyard meeting tomorrow at Pollak Vineyards from 11 am. I won't be there, but here is my handout for tomorrow, which talks about risks of diseases at this point and a disease update at Winchester. Tony will be there to discuss about viticulture topics.

There are chances of rain in next few days in the forecast. However, so far, we haven't had a night which favors downy mildew sporulation for a while. In addition, your berries should be developing resistance to downy mildew and powdery mildew at this point (4-5 weeks after bloom).

For black rot, it may take little longer (up to 8 weeks after bloom, depends on variety), thus, please scout your vineyards for black rot. Black rot fungus takes about 2 weeks from infection to sporulation. Thus, you do not see it right now, your risk is low because there is not enough time to have an outbreak. If you have some degree of infections on berries and leaves at this point, and if you are concerned, Rally (myclobutanyl) is a good product that you can apply after the rain.

Monday, July 13, 2009

Another dry weekend :)

We haven't experienced major disease event for a while. On 7/9-7/10/09, we had two consecutive nights that were favorable for downy mildew sporulation, and on 7/11/09, there was a short thunderstorm (~ 1 hr, 75F, 0.42 inches). It dried up quickly, thus, it may or may not be long enough for downy mildew infection (~ 90 min is required). For some location, it might been an infection event, so, please check your local weather record.

Most of your vines are getting close to the end of the critical period (bloom to 4-5 weeks after bloom) for berry infection by powdery mildew, downy mildew, and black rot. After this period, you can relax a bit.

The next disease to be considered is probably Botrytis. There is no formal study done yet, but many growers experienced that if you apply fungicide before bunch close and varison, the risk of Botrytis outbreak decreases. I think the logic behind it is that the application before bunch close provide a good spray coverage for both outside and inside of the bunch, and the application before varison adds protection when more Botrytis spores tend to be present in the air. There is no fungicide with a curative activity against Botrytis, thus, preventative application is important.

Wednesday, July 8, 2009

No, it's not chocolate truffle...

On Sunday and Monday morning (7/6 and 7/7/09), we had relatively high relative humidity (>80%) at night which favor downy mildew sporulation. Thus, if downy is your concern, you may want to scout your vineyard. (But remember that it requires rain for new infection.)

As I mentioned several times, we have an experimental plot where some of vines are not treated with any fungicides. On these vines, black rot, powdery mildew, and downy mildew become very severe. Last time I showed black rot, so, now it's a turn of powdery mildew.

Powdery mildew on upper leaf surface

Powdery mildew on bunches... No, it's not truffle...

Powdery mildew on a cane

Monday, July 6, 2009

It was a nice and dry weekend

I hope all of you had a nice 4th of July weekend. I'm glad that we did not see the forecasted thunderstorm events.

Most of vines should be approaching the end of the critical period for powdery mildew, downy mildew, and black rot infection on berries. Berries of V. vinifera varieties become resistant to infection after 4-5 weeks after bloom. (V. labrusca vines become resistant after 2-3 weeks, hybrid varies.) These pathogens still can infect, but the success rate declines rapidly after this period. In Winchester, >50% bloom was observed on Chardonnay on 6/6/09 and on Cabernet sauvignon on 6/9/09; thus we have about a week to 10 days to go.

After this critical period, weather condition in VA typically becomes unfavorable for downy mildew and black rot (hot and dry), and powdery mildew control becomes a key issue. Please scout your vineyards for diseases and adjust your spray schedule accordingly. Also, this is about the time Japanese beetle becomes an issue. I've heard that wet spring tends to support their population, so, keep your eyes on them too.

Friday, July 3, 2009

Happy 4th!

The thunderstorm on 7/01/09 lasted a little over an hour (0.73 inches); however, RH remained high for about 9 hours with an average temperature of 65F. Thus the event was long and warm enough for Phomopsis, downy mildew, and black rot infection, and powdery mildew ascospore discharge.

Also, we had nights with relatively high RH (>80%) in 6/29 and 7/2. If these are isolated events, you do not need to worry about; however, as we know, the early part of June was very wet and we had many nights with a favorable condition for downy mildew sporulation. Sure enough, when I checked vines yesterday, we had a lot of sporulations under side of leaves.
If you have seen these spores on many of your leaves, you may want to think about protecting healthy leaves and berries from next infection event, or use materials with a curative activity (Phosphorus acid, Ridomil etc).

The other disease I found quite a bit in our untreated vines are black rot. This is one of diseases which you really need to be on top of it to secure your yield. Here are some convincing pictures.

Here, you can see a path of infection from a leaf to berries...
Now you can clearly understand why it was named black rot...
Once again, the critical period of infection on berries for black rot, downy mildew, and powdery mildew is 4-5 weeks from bloom. If you protect your vines during this period, you should not see damages like these. In fact, a vine next to these vines which received a treatment is nice and clean!

I hope you will have a nice July 4th weekend. If you travel somewhere, please drive safely.

Wednesday, July 1, 2009

Thunderstorm is coming...

The radar is showing thunderstorms for tonight (now I heard the thunder...); however, in the past few days, there is only one night when the condition was favorable for downy mildew sporulation. Since we are approaching the end of critical period, those of you who has not seen much downy mildew can relax a bit once the 4-5 week window has past. If you are concerned about downy mildew based on your assessment of the vineyard and if the vines are not protected, then you can apply Phosphorus acid or Ridomil products after the rain. (The forecast is showing chances of rains coming later in this week.)

We visited a vineyard at Southern Piedmont AREC yesterday. This vineyard is set to test a relatively low input practice (14-day schedule of mancozeb+sulfur is the backbone). This year, they did not experience extensive rains as Northern part. In addition, they managed the canopy very well. As the result, we could not find major outbreak of disease. It tells you that the importance of canopy management (= air circulation) and the incorporation of weather information in your spray schedule. We will monitor the vineyard and see how it holds toward the harvest.

Sunday, June 28, 2009

So far so good.

We had a short thunderstorm event on Friday (26th), but it lasted about 3.5 hours with an average temperature of 73F and a total precipitation of 0.33 inches. It was sufficient for powdery mildew ascospore discharge, and downy mildew infection. We are expecting see some more thunderstorm later this evening.

As I mentioned in the previous post, most of us are still in 4-5 weeks after bloom which is a critical period for berry infection by black rot, powdery mildew, and downy mildew. I'm not advocating excessive application of fungicide here, but just reminding you that this is the critical time. If you have already protected your berries, you do not need to be panic.

So what will happen when you failed to protect your berries? Here are some examples from unsprayed vines in my plot.

Powdery mildew on berries
Black rot on berries
Black rot and powdery mildew on berries...

Thursday, June 25, 2009

Thank you for your attendance.

Thank you very much for attending the vineyard meeting at Doukenie last night. If you could not make it, you can download my note from here. As I mentioned several times in here and in this note, time period between bloom to 4-5 weeks after is the critical time to protect berries from downy mildew, powdery mildew, and black rot for most of wine grapes (V. vinifera varieties). Please scout your vineyards and make an adjustment to your spray schedule, if needed. There are some chance of rain tomorrow and on Sunday.

The average relative humidity was low (~50%) and average temperature was around 71F last night. Now we have five nights without favorable conditions for downy mildew spore production; however, we had so many nights with favorable conditions for spore production during early June, so, keep that in your mind.

Also, in our untreated vines, I start to see more and more powdery mildew. Rain events in last month or so probably provided enough opportunities for powdery mildew fungus to spread spores (ascospores) from its overwintering structure (cleistothecia). Thus, as temperature goes up, we probably see more powdery mildew development. As you know, we have several choices of fungicides for powdery mildew, so, you do not need to panic, but I just want to remind you that it's coming.

Here are some pictures from our vineyard.
The white circle on the center is powdery mildew.
Up close and personal...
(You can almost see spores!)Powdery mildew prefers a location with diffused sunlight.
Such as the shaded leaf on the center of the picture.
Do you see powdery mildew?
I do. ;)

Wednesday, June 24, 2009

Grape root worm + vineyard meeting at Doukenie Vineyard

We found infestation on new vines by these bugs. For more information, please refer to these extension factsheets from Virginia Tech and Cornell University.

Damage on leaves (adults feed on leaves)
(White spots are residues from fungicides)
Culprit: adult grape root worm
We had an another night with low RH (in 70% range). Hopefully this trend continues!

Plus, we have a vineyard meeting this evening (6 pm) at Doukenie Vineyard. I hope you can make it.

Tuesday, June 23, 2009

Nice weather so far!

This may be the first time in a long time that I don't mention about disease risk ;) We had two nights with relatively low RH which makes less conducive for downy mildew sporulation. But remember that we had more than a week long favorable weather for downy mildew. These spores are still out there. Hopefully we do not receive major rain events in the near future.

Our Chardonnay was about 50% pea-size and Cabernet sauvignon was about 100% BB. They are moving fast!!

Sunday, June 21, 2009

I'm back!

Finally, almost a week long meeting is done and I'm back in Winchester. Here's a summary of what happened during last week.

6/15: night time temperature ~64F, RH 7-80% (DM)
6/16: night time temperature ~68F, RH 9-100% (DM)
6/17: night time temperature ~65F, RH 7-80% (DM), plus, rain events from 3:40 am followed by high RH until 3:40 pm (~12 hr), average temperature was about 67F, a total precipitation was 0.64 in: (Phomopsis, Powdery mildew, Downy mildew, Black rot events)
6/18: Rain events from 12:20 am followed by high RH until 6:40 am (~ 6 hr), average temperature was about 60F, a total precipitation was 0.22 in: (Phomopsis, Powdery mildew, Downy mildew, Black rot events)
6/19: night time temperature ~65F, RH 90% (DM)
6/17: night time temperature ~70F, RH 90% (DM), plus, rain events from 8:40 am followed by high RH until 11:40 pm (~3 hr), average temperature was about 73F, a total precipitation was 0.53 in: (Downy mildew infection event). There were several right rains during the night, but RH was too low to account for a major disease event.

Thus, we had a series of weather events which is suitable for downy mildew infection and spore development. If you are planning to apply fungicides next week, it is probably a good idea to include a material that has a good curative (kick-back) activity against downy mildew (Ridomil products, Phosphorus acid products). If you have seen black rots, it may be a good idea to include myclobutanyl (Rally) in your spray mix. Rally has a good curative activity against black rot.

Other thing I noticed in our vineyard is powdery mildew. It is not to the point of concern, but I start to see symptoms here and there. Do not forget to add a material for powdery mildew. Sulfur is a cheap broad spectrum material for powdery mildew.

As you are aware, 4 to 5 weeks after bloom is the critical time for black rot, downy mildew, and powdery mildew infection on berries. Please make sure to protect your bunches.

FYI: our Chardonnay is 100% BB size and Cabernet sauvignon is 50% BB size.

Monday, June 15, 2009

Finally, a nice weekend!

Since the last posting, we had showers on early morning of 6/13/09, but it was not significant in terms of duration of potential wetness event. Night time temperature has been consistently in upper 60F and the relative humidity is ranging from 70-90%. With combination of 10 conducive nights we had, I assume that we still have good conditions for downy mildew fungus to produce spores.

I'll be out of my office due to a meeting until Friday. I should be able to check emails and probably update this blog, but it may depends on how busy I get at the meeting (no, it's not one of fun meetings...).

Saturday, June 13, 2009

Downy mildew gallery

At Winchester, we had light rain events during the night of 6/12/09, but it was short events and the relative humidity was low (80% or so), thus it probably did not promote any infections. However, we are experiencing continuing favorable nights for downy mildew sporulation (average T>55F, high RH (80-100%)) for 10 days now.

Yesterday, we conducted a formal disease assessment, and observed first incidence of powdery mildew for this season. We had plenty of infection events in last two months, so it was not surprising. At this point, it is a trace level of infection on untreated vines. Downy mildew was the major disease so far. We had up to 40% incidence on untreated vines. Next runner-up was black rot. It varies vine to vine, but some of vine had 10-15% incidence. Phomopsis was omnipresent as I expected from early May rain falls, but severity was low overall. We will examine diseases again in the near future, and I will update as the season goes.

Here is downy mildew gallery for your reference. I hope you don't see bunch infection as we found on our untreated vines.

Downy mildew on leaves (oily spot lesion) and bunches
Close up of infection on a bunch
You can observe sporulations (white mass)
Close up of under side of a leaf with heavy sporulation
We are talking about millions of spores at this point.
(= early season management is important!)

Thursday, June 11, 2009

Another thunderstrom...

We had a thunderstorm went through the town yesterday evening around 5:40 pm then there were several rain events throughout the night (~0.48 inches). The relative humidity is still above 90% as of 8:30 am (>15 hours) and average temperature during this wet event is about 65F. As you might guessed, it was an event for Phopmopsis, black rot, downy mildew, and Botrytis infection, and powdery mildew ascospore discharge. Also, we are having 8 consecutive nights with temperature in mid-60F and RH being high (90-100%, except on 6/8/09, but it was still in 80% range). This warm humid nights promotes downy mildew fungus to produce spores.

We are expecting more rains to come in next few days. We'll see...

Tuesday, June 9, 2009


At Winchester, we had a series of thunderstorms went through the area from 3:30 to 6:00 am or so (0.47 inches). The relative humidity was above 90% until around 7:30 am. Thus, it was about 5 hours of wetness with average temperature of 68-69F. It was an infection event for Phomopsis (light infection) and downy mildew. In addition, warm temperature and high RH probably promoted downy mildew to produce spores.

As I type in this post, the sky is getting darker... I guess we will have another thunderstorm this evening.

Monday, June 8, 2009

It was nice and warm weekend, but...

At Winchester, we had four nights (6/4-6/7/09) with average temperature above 55F and average relative humidity in 90% or more. During last night, average temperature was about 69F, and average relative humidity was little low, but still around 80% range. These warm humid nights favor downy mildew fungus to produce spores.

With rain events in weather forecast, downy mildew would be a major concern as I noted in the previous post. Please review your vineyard situations (as I went through in the previous post), and be prepared. Hopefully, rain does not hit us as in forecast, but you never know.

Saturday, June 6, 2009

Finally, a dry weekend!

Thank you for those of you who made to the meeting at White Hall. My handout can be downloaded from the previous post.

The rain is gone for now, and in the last three days, we had about 1.2 inches of rain, and wetness event lasted over 68 hours with average temperature of 58F. As you can imagine, it was good for Phomopsis, black rot, and downy mildew infection, and powdery mildew ascospore discharge. In addition, we had three consecutive nights with temperature above 55F which promote downy mildew sporulation.

We are expecting even more rains next week. If you are in the same situation, please be prepared. Depends on when you applied the last application, what chemical you applied, how much rain you received, which variety you have, and the history of your vineyard, the situation will be different. However, it is blooming-postblooming time when the all major fungal disease can cause damages to your vines. I'm not an advocate of the intensive management, but these series of rain (including incoming ones) may not give you an option. Please spend some time to make an assessment of the situations in your vineyards.

Here are some of potential scenarios.
1) Last application: two weeks ago, mancozeb + sulfur (or similar protective fungicides), vines are in bloom or post-bloom, little or no rain, expecting rain this week --> You will have a wide range of choices. You may stick with economical protective fungicide (e.g. mancozeb + sulfur).

2) Last application: one week ago, mancozeb + sulfur (or similar protective fungicides), vines are in bloom or post-bloom, little or no rain, expecting rain this week --> Here comes a judgment call. If you did not experience rain in the last week, you may able to wait until next series of rain is over and hit vines with curative fungicides (Ridomil or Phosphorus acid for downy, Rally for black rot, etc) plus a broad spectrum protective fungicide such as mancozeb products.

3) Last application: two weeks ago, mancozeb + sulfur (or similar protective fungicides), vines are in bloom or post-bloom, had 2-3 days of rain, expecting rain this week --> Downy mildew and black rot might be your major concern. Consider using products with curative activities (Ridomil or Phosphorus acid for downy, Rally for black rot, etc) plus a broad spectrum protective fungicide such as mancozeb products.

4) Last application: one weeks ago, mancozeb + sulfur (or similar protective fungicides), vines are in bloom or post-bloom, had 2-3 days of rain, expecting rain this week --> Downy mildew and black rot might be your major concern. Depends on how much rain you received, the protection from mancozeb and sulfur may be gone by now. Consider using products with curative activities (Ridomil or Phosphorus acid for downy, Rally for black rot, etc) plus a broad spectrum protective fungicide such as mancozeb products.

5) Last application: one weeks ago, Ridomil+ sulfur (or similar systematic fungicides), vines are in bloom or post-bloom, had 2-3 days of rain, expecting rain this week --> Ridomil should provide you a coverage for 10-14 days. However, consider the history of your vineyard and current situation. If you had a issue with downy mildew or black rot last year, you may need to be on top of the situation. You can scout your vineyard and look for symptoms of downy or black rot (please see images below). If you find downy mildew or black rot in your vineyard (say, few leaves per vine), then you may need to think about protecting your leaves against the upcoming rain events. If you know vineyards are clean (historically and right now), then you may be able to hold off your application until after the upcoming rain events. Either way, downy mildew and black rot might be your major concern. Consider using products with curative activities (Ridomil or Phosphorus acid for downy, Rally for black rot, etc) plus a broad spectrum protective fungicide such as mancozeb products.

The other disease of concern would be Botrytis. It can cause infection on flowers and cause problems later in the season. You may want to include some of Botrytis materials such as Elevate, Endura, and Pristine in your program. And although I did not mention in the previous scenarios, you still want to protect your vines from powdery mildew. Sulfur would be a nice and economical insurance. If you decided to use other products, such as Sterol-inhibitors, please make sure you rotate the mode of action of the chemical.

Here are pictures of downy mildew and black rot for your reference:

Downy mildew "oily spot" symptoms, upperside of the leaf
Downy mildew sporulation, underside of the leaf
Black rot symptom

Friday, June 5, 2009

Rain, rain...

It rained from 11 am yesterday at Winchester, and the rest of the day was wet (0.18 inches). It accounted for at least 13 hours of wetness (+ continuing today) with a mean temperature of 58F.

As you can imagine, even though the temperature was low, it was long enough for Phomopsis, black rot, downy mildew infection, and powdery mildew ascospore discharge.

We'll have a meeting at White Hall vineyards today(6/5/09) from 11 am. I'll talk about biology of major fungal diseases for VA wine grape using Powerpoint. The contents will be similar to the other talks, but you get to see more pictures. ;) Tony will be there to talk about seasonal update as well.

Thursday, June 4, 2009

Thank you for your attendance.

Thank you for those of you who made to the meeting. If you missed it, you can download my note from the previous post.

We had a thunderstorm last night and it rained from 7:20 to 8:20 pm. The relative humidity was above 90% for 5 hours or so afterwards, and temperature was in mid-60F. Then temperature went down to upper-50F, and as a consequence, the RH went up. It was a windy condition, so, I'm not sure leaves were wet the whole time, but if it was, it was about 12 hours of total leaf wetness with temperature ranging from 68-55F. It was good for Phomopsis, black rot, downy mildew infection, and powdery mildew ascospore production. (note: If leaves dried out after 5 hours or so, then it was good for light infection for Phomopsis, downy mildew infection, and powdery mildew ascospore production.)

We are expecting more rain events today, but temperature seems to be low (mid-50F). Hopefully, it will be low enough so that downy mildew won't be too happy.

Tuesday, June 2, 2009

Vineyard meeting at Linden tomorrow from 11 am

As Tony mentioned in his email, we will have a series of vineyard meetings this week. The first one is tomorrow at Linden vineyards, starting from 11 am. I'll talk about early season disease management, similar to what I presented in previous meetings, but I added a section for Botrytis. You can download the note from here. Tony's student Mr. Tremain Hatch will talk about nutrition management, and Dr. Chris Bergh from our station will talk about grape berry moth research.

The next meeting will be held at White Hall vineyards on this Friday (6/5/09) from 11 am. I'll talk about biology of major fungal diseases for VA wine grape using Powerpoint. The contents will be similar to the other talks, but you get to see more pictures. ;) Tony will be there to talk about seasonal update as well.

Monday, June 1, 2009

Started blooming!

Our Chardonnay started to bloom yesterday. It was about 0-10% blooming yesterday and now it is about 15-50% per vine (variability among vines), and each cluster is about 10-50% open. Cabernet sauvignon are still holding tight.

Sunday, May 31, 2009

Rained again. :(

Last night, we had several rain events which accounted for about 5 hours of wetness. Average temperature during that period was about 60F, and total amount of precipitation was 0.17 inches. It could be a light infection event for Phomopsis, powdery mildew ascospore discharge, and downy mildew infection. (little too short for black rot infection)

I went back to the vineyard and took a look at the leaf lesions I showed here on Friday.

Sure enough, there are sprangiophores (a tree-like structure containing spores) coming up from the underside of the leaf. As I mentioned in Friday's entry, it takes 1-2 weeks to develop spraongiophore, thus, the infection probably took place during 5/16-17 rains (I wrote 17-18th, but it was 16-17th).

We are expecting few more chances of rains during this week. If your vines are close to bloom or blooming, please be ready to protect your vines.

Friday, May 29, 2009


Yesterday, thunderstorms passed by Frederick county from around 4 pm to 5pm. There were other rain events afterwards, and the relative humidity was high until 7:30 am or so. It accounted for >15 hours of wetness event with average temperature of 68F or so. Total amount of precipitation was 0.47 inches. It was warm and long enough for Phomopsis infection, powdery mildew ascospore discharge, black rot infection, and downy mildew infection.

Also, now we are having 5 consecutive nights with temperature above 55F with the relative humidity in 80-100% range which can promote downy mildew sporulation.

Speaking of downy mildew, I started to see potential downy mildew lesions on some of our untreated vines. Typically, after infection, "oily spot" will show up on the upper surface of a leaf, then you will see "downy" fungal body on the underside of the leaf. This downy fungal body mainly consists of many sporangiophores which look like a tree of sporangium. Sporangium contains spores called zoospore which causes next round of infection. It will take 4 to 5 days after infection to symptom development, thus, I'm seeing either one from rains during May 17th to 18th or the current series of rain events from may 25th. It will take 1 to 2 weeks after infection for production of spores. I was rained out after taking this picture, so, I'll go back in the field later today to look for more.

Thursday, May 28, 2009

Still wet...

In the past few days, we had about 2 inches of rain at Winchester, but I heard that there were up to 5 inches rains observed in some places. Since the afternoon of May 25th, we have been having either rain or high relative humidity conditions continuously (RH is still above 90% as of 10:30pm 5/28/09, thus potentially, we have > 60h of wetness). Average temperature during this period was 67F in 25th, and 60F in 26th and 27th. These conditions are good enough for Phomopsis infection, powdery mildew ascospore discharge, black rot infection, and downy mildew spore production and infection.

If your vines are very close to bloom or blooming, it is the critical timing for many of these disease development. As I mentioned earlier, there are some fungicides you can use after infection events. For powdery mildew, you can use any of fungicides you typically use (even sulfur) because the fungus grow on grape tissue superficially. For black rot, Rally (mycrobutanil) has a good curative effect. For downy mildew, Ridomil products and Phosphorus acid products has a good curative effect. No curative fungicide against Phomopsis. You can apply these products up to 6 days after infection in most of the cases, but to be safe side, it is probably wise to apply 2-4 days after infection. (because downy mildew and powdery mildew may take only 7 days after infection to produce spores under optimal conditions)

As I mentioned yesterday, disease developement depends on many factors. I'm showing these infection information to aid your decision making process, but ultimately, you are the one who know more about your vineyards than anybody else. For example, you may have sprayed last week, your vineyard may have received only 1 inch of rain, and the vines may not be ready for bloom. Then you do not need to panic. In addition, please think about history of your vineyards, varieties, etc. Also, don't forget about cost of application (to your wallet and to the environment) too.

Tuesday, May 26, 2009

Now it's raining...

It looks like we will have a rainy week. Since Saturday, we had three nights with average temperature above 65F with the relative humidity in 80% or more at Winchester. These warm humid nights are favored by downy mildew sporulation from infected leaves. And these series rain events will help them to infect leaves, rachis, and berries. Thus, it is possible that downy mildew had a chance to produce spores during these nights, and these spores are ready for infecting grape tissues. Therefore, for the next round of application, you may want to think about adding a fungicide for downy mildew with curative activity such as Ridomil products.

But once again, the risk of diseaes development depends on the history of your vineyard and other environmental conditions such as variety, traning system, etc. If downy mildew has not been a problem in the past, the risk may be less.

Sunday, May 24, 2009

No significant rain so far!

There was a sprinkle in the morning, but so far, we haven't experienced a significant rain event yet at Winchester.

Our Chardonnay and Cabernet sauvignon have been moving its growth stage. It was about 8-90% with 8-9 leaves unfolded with elongation of rachis (E-L 15) for Chardonnay, and about 3-50% E-L 15 for Cabernet sauvignon. Cab sauvignon has more variation among vines, which is consistent since bud break.
I start to see development of black rot lesions on untreated vines. It takes 2-3 weeks to develop fruiting bodies (black specks within tan colored lesion), thus, rain events during 5/5-5/7 or 5/11 are probably responsible for the infection.
I hope you do not see many of these symptoms in your vineyard. If so, you need to protect your berries very well so that it won't affect your yield. Mancozeb, captan, and azoxystrobin (Abound) works well as a protective fungicide application, mycrobutanyl (Rally) works well as a curative fungicide, but I doubt that it will kill actively sporulating lesion. The efficacy will be against new infection. Also, if you happen to have mummified bunches hanging from the old shoots, please take them out. It will serve as a source of inoculum through out the season.

Friday, May 22, 2009

Rain forcast on next few days.

(Today's picture is our friend Phomopsis again!
Left side has more spots probably because it is closer to the vine
where the fungus survives and produce spores.
Spores were rain splashed to the leaf to cause infection.)

It seems that pretty much all over Virginia is expecting some type of rain during next few days. I do not know how "30-40% chance of thunderstorm" turns out, but if your last spray was more than two weeks ago and/or your vines have grown a lot from the last application, then you may need to be prepared for these chances of rains. As I noted yesterday, please adjust your spray materials and spray amount based on your vine's growth stage.

Thursday, May 21, 2009

Thank you for your attendance.

I appreciate those of you who showed up at the meeting. I'll try to visit the meeting in the other regions as much as possible. [I do have a research to do, so, I cannot go to every single one of them, though. ;)]

It looks like we will have good weather during next few days, and I think most of you are thinking about pre-bloom or at-bloom applications right now. (Those of you in the Southern VA may be thinking about 1st application after bloom.) Temperature is getting higher (although we had 3-4 days of cool nights), and many of common disease organisms are more active around 60-75F. At pre-bloom, you need to think about Phomopsis, powdery mildew, black rot, and downy mildew control, and for at-bloom or the first application after bloom, you need to add something for Botrytis control. Pre-bloom to 2-3 sprays post-bloom are very critical sprays for disease control in VA growing area.

Rachis and flower part can be infected by these fungi and results in direct problems, and also, in some cases, such as powdery mildew infection on rachis and small berries, it could cause problem later in the season by creating wounds for other microorganisms to come in to cause sour- or bitter-rots. Botrytis infection on flowers may also come back as rots later.

If you have an application due soon, make sure to adjust your spray volume based on the canopy development, and remember that you should not apply sulfur if temperature is85F or above.

Last two nights were cold (lower 40's) around Winchester. It was not suitable for downy mildew sporulation event. I hope you did not experience any frost injury. Growth stage was about the same as the last time for our Chardonnay and Cabernet sauvignon.

Tuesday, May 19, 2009

Central VA vineyard meeting at Lovingston tomorrow

A vineyard meeting will be held at Nelson extension center (just south of Food Lion on Thomas nelson Highway (Hwy 29)) at Lovingston from 11 am. I'll be talking about the same early season disease management information I presented at the previous meeting.

The temperature in the morning did not go down enough to cause damage on our vines. I hope your vines are OK as well. These two nights are too cold for disease development.

Our Chardonnay was ~90% 7~8 leaves unfolded (I have not observed rachis elongation yet), and Cabernet sauvignon was about 8-90 % 7~8 leaves unfolded. I'll probably apply pre-bloom applications in the near future.

Monday, May 18, 2009

Another frost advisory tomorrow morning (5/19/09)

Our low was low 40's this morning. It suppose to be warmer tomorrow and I hope that we do not get any frost damage. We'll see.

We received several disease samples today which I'd like to share with you. The first one is crown gall. This is caused by a bacterium called Agrobacterium vitis. This gall formation is due to genetic modification caused by the bacterium to the infected grape vine. Sometimes it is only a cosmetic damage, but the gall tissue could girdle the vine and restrict the movements of water and nutrients, then results in the death of the vine.

There are some chemicals and biological agent available against gall formation and prevention of the disease, but as far as I know, none of them are very effective as you would expect from other chemical treatments such as fungicides. Removal of the infected vine and then replacing with a certified vine is the common method of management. However, you need to keep in your mind that this bacterium can survive in infected roots and soils up to 5 years. (This bacterium causes a systematic infection, thus if you see the gall, the bacterium can be in roots.) Some of grape phylloxera resistant rootstocks (3309C, 101-14, Riparia Glorie, etc) are known to tolerate the disease.

The other sample is our old friend Phomopsis, caused by a fungus Phomopsis viticola. The first picture shows the case when the rachis is infected. With three weeks of rain after rain, this year has been a Phomopsis year so far.

And the one on your left in this picture is showing splitting of epidermal cell which is also associated with Phomopsis infection.

Unfortunately, we do not have fungicide with a curative activity against Phomopsis on grape. Thus, once the damage has done, nothing much you can do about it to fix it. (You can remove infected shoots at your shoot thinning, though.) You need to remember next spring to protect new growth because the old infected woods can produce spores for 2 years or more.

Sunday, May 17, 2009

Frost Advisory tomorrow morning.

As you may noticed, temperature has been declining since this morning. National weather service is issuing frost advisory from 4 to 9 am tomorrow (Monday) morning for Frederick county. Please check your local weather. Recent series of rain events are providing enough moisture to vines to push their shoots rapidly, and these succulent tissues are sensitive to stresses. If you are the lucky one with one of air circulation systems (propeller etc), this may be the time to use it. Hopefully, your vines won't experience frost damages.

Our Chardonnay was about 80% 7-8 leaves unfolded (~10-inch or longer), and Cabernet sauvignon was about 20% 7-8 leaves unfolded (7~10-inch) as of today.

(Phomopsis symptoms on a vine in our experimental vineyard, 5/17/09)

As for disease concerns, we experienced rains and thunderstorms yesterday from 6:20 pm to 10 pm, then there are light rains here and there until 2 am or so. The relative humidity was above 90% until 3:20 am. Temperature started off with 64 F and ended with 55.4 F during this >9 hour of wetness period. It was good for Phomopsis infection, powdery mildew ascospore discharge, and downy mildew sporulation.

Friday, May 15, 2009

A wet night and more rains to come

It turned out to be a very nice day for planting at Winchester. We almost finished planting of two vineyards (a total of 1/2 Acre with Chardonnay and Merlot) which will be used for chemical trials and other management-related experiments. We had a drizzle in the early morning, but the expected thunderstorm did not arrive until 8pm or so and it was not as severe as I expected.

On 14th, night time relative humidity was high, but temperature was low (low 40's), thus it was not a disease night. But last night, we had a series of short rains and temperature stayed in low-60's with the relative humidity above 90% until now (8am, fog). This >12 hours of wetness accounts for Phomopsis, black rot, powdery mildew, and downy mildew infection events.

We are expecting to see more rains during this weekend, so, please think about potential disease events (in the future or in the past) when you decide for a fungicide application. You can find details of infection events I'm describing here in my notes from past vineyard meetings (you can find them in this blog, or in my AREC webpage).

The growth stage of Chardonnay in our vineyard was 15-20% with 7-8 leaves unfolded (but I did not see significant elongation of the cluster yet, thus between E-L 12 and 15), and that of Cabernet sauvignon was 8-90% with 5-6 leaves unfolded (~7-10-inch, E-L 12).

Wednesday, May 13, 2009

Thank you for those of you showed up at the vineyard meeting

Thank you for those of you showed up at the vineyard meeting, and we thank Jeff to host the meeting. The notes I used at the meeting can be downloaded from here.

Last night was another cool night around Winchester. The relative humidity was high (~90%), but average temperature was 48F or so, and it was little too cold for downy mildew sporulation.

We are expecting some thunderstorms passing by during next few weeks, and temperature is expected to be in 70's. Depends on when your last application was made and how much new growth you have observed, you may need to protect new growth against this series of rains.

I'll be planting my vines tomorrow. I hope I won't be rained out...

Tuesday, May 12, 2009

We have a vineyard meeting tomorrow at Glenn Manor

We are having nice sunny days! Some of shoots in our Chardonnay elongated to 10-inch or so (start to passing E-L 12 stage). And Cabernet sauvignon is catching up with Chardonnay. About 7-80% of shoots are 5~7-inches (E-L 12).

A day before (5/11/09), we had fairly dry (~50% RH) night. We had a shower (0.03 in) in the yesterday evening (5/12/09). It lasted only 40 min or so and the RH did not stay high, thus it probably was not enough for any disease event. The night time RH was high (nearly 100%), but temperature was in mid-40s. Thus, it was not good for downy mildew spore production either.

We will have a vineyard meeting at Glenn Manor vineyard and winery from 11 am tomorrow. I'll talk about early season disease management tips as I did last time, and this time it includes information on downy mildew. If you cannot make it, you can download my notes from here.

Sunday, May 10, 2009

Nice weekend weather!

It has been a very sunny weekend in 70's. I can take this anytime.

Last night, RH was 4-50% and temperature was around 64F. I think it was little too dry for downy mildew to be happy. Speaking of disease, I found some leaves and canes showing an initial symptom development of Phomopsis today. We have untreated vines for disease observations, and I'm hoping that these vines will provide us nice cases of diseases throughout the season.

The hard-to-see dark spots with yellow hallo are from Phomopsis infection on leaf. If you take a look at shoots, what you see is:
Small necrotic spots (around the center) which can be expand later in the season. Dr. Mike Ellis' group at the Ohio State is currently working on the infection process of this fungus. Based on observations on the production of the fruiting structure in my previous experiments, it looks like this fungus can spread underneath the epidermal tissue even if we do not see clear symptoms. At which point the spread occur is not known yet.

Our Chardonnay were about 9-100% 10-inch (E-L 12) and Cabernet sauvignon was about 7-80% 5~7-inch (E-L 12) as of noon today.

Saturday, May 9, 2009

No rain, so far...

At Winchester, we did not experience the forecasted rain event yesterday (5/08/09). It was a light shower in this morning with trace amount of precipitation. One thing I noticed was the night time temperature. It was above 68F with relatively high relative humidity (mostly in 8-90% range). Under this condition, downy mildew fungus (it's not technically a fungus, but I call it fungus for convenience) can produce a structure called sporangiophore which is basically a tree of sporangia which contains spores called zoospores.

Typically, we consider the risk of spore production is high when there are more than 3 consecutive nights with temperature above 55F with high RH. Night time temperature in last few days are (5/6/09: lower 50's, 5/7/09: lower 60's, 5/8/09: lower 50's, and 5/9/09: upper 60's), and you know the RH was high. The first potential infection event was on 5/4/09 around Winchester, and it takes 7 days (depends on temperature) to produce spores. Even if the 5/4/09 rain was not enough, we had a plenty of rain events after that. Thus, if the trends continues, the conditions for spore production will be met in the near future. I'll keep updating on this.

But please do not panic. I'm just talking about biology of this fungus to inform you that even though you may not think of it, the life of fungus is moving along with the season. They do not come out from nowhere like a magic. (at least for major fungal diseases for grape) It takes its steps, but we cannot see it. Protective fungicide application will protect your vine from infection, and as I noted several times, the situation is different in each vineyard.

Friday, May 8, 2009

Finally, the sun is out!!

As you probably noticed, the sun is out! And grape vines are moving fast. Our Chardonnay and Cabernet sauvignon has moved quite a bit as well. About 7-90% are 5-7 inches (E-L 12) and about 5-70% are 5 inches (E-L 12) for Chardonnay and Cab sauvignon, respectively.

Yesterday (5/07/09), Winchester area had a brief shower (0.12 inches) from 10:25am (64.4F) to 12:00pm (64.4F), and the RH was >90% until 1:00pm. And then a very short thunderstorm from 3:40 to 4:00pm (69.8F). The first event was bit short for Phomopsis and black rot infection events; however, it was probably enough for powdery mildew ascospore discharge and downy mildew infection event. A mild temperature range favors both mildew pathogens too.

Some of varieties are probably getting closer to the bloom, and you need to start thinking about these mildews. 2-3 weeks pre-bloom is the start of critical period for downy mildew rachis and berry infection. Make sure that your spray program has something against downy mildew (mancozeb, captan, etc for protection, and metalaxyl (Ridmil Gold MZ etc) for curative and/or protection). Once again, the risk of a disease will depends not only on the local weather condition but also on disease history of your vineyard, training system, variety etc.

We are expecting see yet another rain events today and tomorrow. I hope that you had a chance to apply whatever you needed.

Thursday, May 7, 2009

At Winchester, yesterday's (5/6/09) rain started from 5pm (60.8F) and ended at 6:40pm (59.0F); however, the RH was >90% until this morning (8:40am). A total amount of precipitation was 0.05 in. Thus, it probably accounted for >14h of wetness with upper 50's in temperature (F). It would be enough for Phomopsis, powdery mildew ascospore discharge, black rot, and downy mildew infection. (I feel like I'm repeating myself...)

Please do not get overwhelmed by my report of infection events. I'm just giving you the information about what could happen based on weather conditions observed. If you applied your protective fungicide application, it should stop infection. In addition, there are chemicals with curative (or kick-back) activity against powdery mildew, downy mildew, and black rot. Moreover, the risk of infection by these fungi depends on the history of your vineyard too. For example, if you had a history of outbreak of downy mildew year after year, you tend to have higher risk of downy mildew simply because there are more inoculum (winter-surviving oospore of downy mildew fungus) in your field. In that case, you need to be on top of the situation, and you may want to protect vines from early season to minize the risk of an outbreak later in the season. But if your vineyards have been relatively clean, there may not be enough inoculum to be concerend at this moment.

Wednesday, May 6, 2009

Growth stage as of 5/06/09

Plenty of water affected growth too. About 10% of Chardonnay were 5-7 inches (E-L 12). Growth of Cabernet sauvignon was not as dramatic as that of Chardonnay. As with yesterday, 6-70% of shoots are 3-inch (E-L 9) and others are 1-2 inches.

I think I saw the sun today...

Yesterday's (5/5/09) precipitation at Winchester was 0.27 inches starting from 4:20pm (55.4F) and ended at 9:20pm (53.6F); however, the relative humidity was almost 100% until midnight. Thus, >8 hr of wetness with mid 50's temperature probably accounted for Phomopsis light infection, powdery mildew ascospore discharge, and downy mildew infection.

We had overcast weather this morning, and I hope that you had a chance for application (if needed). We are expecting more rain in next few days and next break could be during this weekend.

Tuesday, May 5, 2009

Much needed break from rain

We experienced a whole day of rain yesterday (5/4/09). Average temperature was 52F, and amount of precipitation was 0.76 inches. The total length of rain event was over 30 hours, including a day before and early this morning. Needless to say, it was long enough for Phomopsis, powdery mildew, and black rot.

Our Chardonnay had grown since the last observation. Average was about 60% 3-5 inch stage. Cabernet sauvignon still varies with vines, some vines are showing 6-70% 2-3 inch stage and others are showing 7-80% 1-2 inch stage.

We are having a break from rain today in most of central and northern VA. I hope those of whom with concern on Phomopsis had a chance to apply your treatment.

Monday, May 4, 2009

Rain, rain, rain...

The ongoing rain event since yesterday morning (5/3/09, 8 am) has been relatively cold. Starting temperature was about 52F, at mid-night it was 49F, and it has been lower 50's today. It is low, but long enough (>33 hr so far) for Phomopsis to cause light (5-15% disease severity on a cane) to moderate (15-25%) disease. In addition, as of this morning, we have received 0.84 inches of rain since last week (and it’s still raining as of 4 pm, but looks like the end is coming!!). As for powdery mildew ascospore discharge, this rain event met the requirement.

A typical rule of thumb for fungicide re-application is “2 weeks or 1 inch of rain, whichever comes first” (Note: you need to adjust the time between applications based on the growth of vine). Please check your local weather for rain and temperature information. There is a banner of “weather underground” on the upper-right side where you can check your local weather information in detail by typing in your zip code (you can even go back in days to see what happened in the past few days).

For example, we applied mancozeb + sulfur on April 30th, but vines have grown an inch or more since then. It seems that when there is a break from this rain later this week, we need to apply fungicide for Phomopsis and powdery mildew to add protection to new growth. Please note that it typically requires at least 2 hours of dry period for a fungicide to properly adhere to the plant surface.

Since rain events in these several days are relatively cold and continous (black rot fungus' spore requires a few hours of dry event to adhere to the grape tissue surface), I think the risk of black rot is low at Winchester. (Also, if you have mancozeb or Ziram for your next application, it will cover black rot too.) However, I encourage you to check your local weather, especially you had black rot issues in the past. As you may know, if you have mummified berries from last year hanging from your vines, it increases a risk of black rot thoughout the season, so, please take them out. [FYI: If you think the risk of black rot is very high in your vineyard, you may apply mycrobutanil (Rally) which has a good kick-back activity, but at the same time, you probably want to save it until later to protect your berries. It will be your judgement call.]

Rain probably makes you think about downy mildew too. It has been warm enough (>50F during the rain) for its over-winter structure (Oospore) to produce spores (zoospores). However, it requires warmer weather (65-75F) to grow and reproduce in a significant way. In addition, chemicals for Phomopsis (mancozeb, captan, Ziram) and black rot (mancozeb and Ziram [captan is not as good as Mancozeb against black rot]) also have an efficacy against downy mildew.

I sent a note through the "grape note" email list today which talks about early season grape disease management tips. If you wish to receive email from either our viticulturist Dr. Tony Wolf or me, please send me an email so that we can add your name to the list.

Sunday, May 3, 2009

Update on growth stage: Chardonnay was about 70-90% 3-inch growth; Cabernet sauvignon was still about 50% 1-2 inch growth with a variation among vines. Still raining as of 6:45pm...

Rain again!

Yesterday, Winchester had a drizzle during 3-4am with an average temperature of 58F. It was not a major rain event; however, the relative humidity was almost 100% until 10am. In addition, we had a rain event from 8:30 to 9:30am with an average temperature of 55F. A combined precipitation was 0.08 inches.

If you separate these events, it was not enough for Phomopsis to cause disease. However, since the relative humidity was high during the night, I tend to think it was a continuous event. If we combine both rain events, it was enough for a moderate infection (15-25% severity) for Phomopsis. Considering how wet it has been, ascospore discharge of powdery mildew was probably initiated with these rains (especially after 3 am one) whether you combine events or not. (but the morning rain might have washed spores off from leaves... a wishful thining ;))

I was running 10K for Apple blossom festival during the morning rain. It brought temperature down and was nice for me, and after the rain, we had a really nice Saturday afternoon to enjoy the parade.

We are having a yet another rainy day. It started around 8am and still going as of 10am. A radar image is showing green around Winchester...

Friday, May 1, 2009

Warm rainy day

At Winchester, we had rain from 11:50am to 2:20pm (0.12 in) with starting and ending temperature of 62.3 and 67.8F, respectively. Relative humidity dropped soon after the rain and still declining at 5pm and the wind was constantly blowing at 5-10 mph, thus, leaves are probably dried one hour or so after the rain. (If the leafwetness measurement is not available, I use RH>90% as an indicator for the leafwetness after the rain.) Three hours or so was not enough for Phomopsis infection, but it was warm enough for powdery mildew ascospore discharge.

Yesterday (4/30/09), we took an advantage of a calm cloudy day and applied our first fungicide application (mancozeb 3 lb/A + sulfur 3 lb/A). Primary target at this point is Phomopsis and Powdery mildew.

Although it was either raining or overcast, average temperature in the past few days were in 50's and 60's, and grape were moving its growth stage. About 70% of our Chardonnay was 3-inch stage, and Cabernet sauvignon was about 50% with 1-2 inch stage (still variable, some are just after bud break).