Virginia Grape Disease Updates

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...

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 ...

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.

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!!

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 ...

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...).

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 ga...

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...

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.

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.

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 ...

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.

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.

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.

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.