Virginia Grape Disease Updates

Just an update on yesterday's post: At Winchester, AREC, a total leaf wetness hours was 29 hours, with an average temperature of 67F. Thus, this rain event was warm and long enough for both downy mildew and black rot. Also, it was long enough for Botrytis as well. For the details of downy and black rot kick back activity fungicides, please refer to yesterday's post.

Well, it looks like we will see more rains coming in next week or so. Sounds like a typical start of the season for VA vineyards, doesn't it? Since most of vines have 2-10 inches of shoots, our main focus will still be Phomopsis , especially if your vineyard(s) experienced Phomopsis in the past.  At Winchester, we are experiencing 27+ hours of wetness with the average temperature of 48F or so. This will be a low Phomopsis risk event, and counting. Plus, especially if you had a serious downy mildew issue in the past season, it may not be a bad idea to think about downy mildew because the next series of rains for this weekend and early next week may happen when air temperatures will be in 60's and 70's.  As for Phomopsis, a protective spray of mancozeb, captan, etc. is pretty much the only mean of management, but we do have some options for downy after the rain event. So, if you did not spray before this series of rains, but you are lucky enough to have a window for a s...

Since we are expecting heavy rain event on Saturday, plus about to be done with the critical time for cluster infection by downy mildew, powdery mildew, and black rot (which last 4-5 weeks after bloom), I received a several emails about the application timing.  As with other timings, it really depends on so many factors, but here's my take on it.      If you have a history of black rot and downy mildew in your vineyard, you may have a higher disease risks.  If you are in this situation, AND if you think that your previous application was waring off, then you may need to apply some protection before the rain.  However, if your previous application was within 7-day or have not seen many rains, or not having much issue with downy or black rot, then you probably do not need to panic.     A good news is that it looks like we have an opening after the Saturday's rain event.  (then a few more days of rain in the early part of the week)...

Winchester area received a series of rain over the weekend, and it looks like we may see more coming in the next few days.  There were three days of low and moderate Phomopsis infection risk events over the weekend.  Also, humid and warm nights can promote development of downy mildew spores.  At this time of the season, what we typically recommend is either mancozeb or captan mixed with sulfur to protect young shoots and leaves.  The reason why I typically do not recommend a use of newer materials such as Revus or Phosphite for downy or Luna or Rally for powdery is because we want to keep it for the critical time for cluster infection, which is from bloom to 4-5 weeks after bloom.  If this warm temperature continues, the bloom may comes soon, though!!

Two days of intermittent rain brought a low infection risk event for Phomopsis.  Also, these spring rain events can be precursor events for both downy and powdery mildew.  As noted in the previous posts, keep protecting young shoots from these pathogens.  At this point, you can use mancozeb, captan, and sulfur. (Note: for some reason, this post was not posted in a timely manner.  Sorry!)

As usual, we start our season with rains.  It has been more than 13hr of wetness so far at Winchester with an average temperature of low 50s.  It has accounted for a low risk of Phomopsis infection, and a line of rain just passed the area too.  We will see how it will turn out over the weekend. As shoots extend rapidly in the early part of the season, the new tissues are not protected by the previous application of fungicide(s).  Keep in your mind to protect these new tissues. I often am asked about when to reapply fungicide(s) after rain.  An often discussed rule of thumb is: < 1 inches of rain: Continue with intended spray interval 1-2 inches of rain: Consider shortening your spray interval in half.  (E.g., if there is 7 days remaining for the normal spray interval, shorten it to 3-4 days) >2 inches of rain: Consider re-application soon. However, please note that it also depends on the history of your vineyard(s), cultural practice, and a...

I had a meeting and did not able to post it in timely manner, but there was a wet event on Monday-Tuesday this week.  It was 14+ hours of wetness and average was around 60F.  It was a risk event for downy mildew, and very low risk for Botrytis. Other than a slight chance of rain tomorrow, it looks like we will have a nice cool week!  For the late season spray recommendations, please refer to previous posts. http://grapepathology.blogspot.com/2014/08/note-on-sour-rot.html http://grapepathology.blogspot.com/2014/08/last-stretch-spray-consideration.html

A line of rain went through Winchester area resulted in 10 h of wetness with an average of 69F.  It was downy and low Botrytis risk event.  Please refer to the comments on previous posts on late season disease management. FYI: Our Chardonnay berries are hitting 20-21 Brix and pH is getting near 3.0.  We will see what the forecasted thunderstorms towards the end of this week will do for it...

I was away for several weeks for a series of meetings, and of course things happen when you are not around... 7/28: 9 hours of wetness, around 66F (low Botrytis and downy risk event) 8/6:   12 hours of wetness, around 64F (low Botrytis and downy risk event) 8/7: 13 hours of wetness, around 57F (probably not much of risk event) 8/11: 19 hours of wetness, around 60F  (low Botrytis and downy risk event) 8/13: 13 hours of wetness, around 60F  (low Botrytis and downy risk event) 8/20: 14 hours of wetness, around 65F  (medium Botrytis and downy risk event) 8/23: 6 hours of wetness, around 65F (low Botrytis and downy risk event) 8/24: 10 hours of wetness, around 62F  (low Botrytis and downy risk event) I will have a few more updates coming up...

As we expected, Winchester area had a wet weekend.  We had to major rain events, which resulted in 11 hours and 10 hours of wetness, both are in upper 60F to lower 70F range.  These are downy mildew and Botrytis risk events.  Once again, humid nights we are experience can be a precursor event for downy mildew risk events because these nights favors spore production of downy mildew pathogen.

Winchester area received a shower yesterday, resulted in 5+ hours of wetness in lower 70F.  It was an infection risk event for downy mildew, and very low infection risk event for Botrytis.  In addition, we observed dews in the last two nights, indicating high humidity, which can trigger downy mildew to produce spores.  As usual, late season downy tends to appear on younger leaves on the top of the canopy.  Please keep eyes on them!  There is a chance of rain on Sunday and Monday.

Winchester area had a wet weekend.  We ended up having 9+ and 16+ hours of wet events, and both of them are in upper 60F.  Needless to say, these were disease risk events for downy mildew and Botrytis.  These were events for black rot too, but the clusters should be resistant to infection at this point.  Looks like we are expecting some rain during this week too.  Please keep your eyes on downy mildew.

After 13+ hours of wetness on the 13th-14th rain event, we had another wetness event starting from last night.  It resulted in 11 hours of wetness with an average temperature near 70F.  It was infection event for downy mildew, black rot, Phomopsis and Botrytis.  With the back to back rain event and high humidity during the night, I would keep eyes on downy mildew development.  It tends to show up on younger leaves (at the top of the canopy) first.  Also, many of varieties are about to be berry-touch/bunch closure stage, which is one of timings for Botrytis application.

Winchester area received a shower yesterday (11th, very early in the morning) which resulted in ~7 hours of wetness with an average temperature of high 60F.  It was risk event for downy mildew (with a good chance of spore production because it was a night time event) and Phomopsis, and a borderline case for Black rot.  (once again, please note that your berries should have become more resistant to downy, powdery, and black rot infection at this point).  Since we had a back-to-back rain event, please keep eye on next potential rain for downy mildew, especially you are due to a next application.  There are chances of rain on Monday and Tuesday.

A thunderstorm went through Winchester area yesterday evening, resulted in 12+ hours of wetness (on going) with an average temperature of near 70F.  This most likely to be resulted in risk event for downy mildew, black rot and Botrytis. However, please note that the risk of black rot (especially on clusters) should be low because vines are about to be done (or already done) with their critical period for cluster infection.  (Plus, if you have not seen much black rot until this point, the risk is low too.)  The same goes with downy mildew cluster infection, but downy mildew can still infect leaves, especially the young ones. People in the south and some early varieties in the north is approaching bunch closure.  This is one of application timing for Botrytis so that we can get the material to the inside of the clusters.

Winchester area was rained out pretty much whole day yesterday, resulted in two wetness events, one with ~16 h of wetness with low 60F, and another one with ~7 hours of wetness with high 50F.  These resulted in infection risk event for black rot, downy mildew, Botrytis and Phomopsis.  Once again, please try to be on top of the situation while we are in the critical period for cluster infection.

A thundershower hit Winchester area around 6PM last night, resulted in 16 hours of wetness with lower 60F in average temperature.  It was disease risk event for black rot, downy mildew, Phomopsis, and Botrytis. As with last few rains, it resulted in a warm and humid night that helps downy mildew to produce spores.  Many of us are still in critical period for cluster infection, and this is the time of the year to be on top of the game.  Please refer to previous few posts about spray ideas.

Boy, what a week! Winchester area received about 17 hours of wetness with average temperature of 20 C (68F) on the 11th, 14 hours of wetness with average temperature of 22 C (72F) on the 12th, and right now on-going wetness with 17hour + with an average temperature of low 20C (68F). These events are warm and long enough for downy mildew, Botrytis, Black rot and Phomopsis.  On top of that because of evening rain events, night time conditions have been favoring downy mildew development.  Our main concern is downy and black rot since our clusters are currently in critical period.  These berries are susceptible to the infection by these pathogens. It looks like the weekend weather is promising, and a 10-day forecast is calling for a chance of rain again on Tuesday... what can we do? For our vines, the last application was made 10 days ago, and we received a total of 1.47 inches of rain at the site.  Last application was mancozeb + sulfur + Phosphite (Prophyt, Phos...

The rain event started on the night of the 8th resulted in about 14 hours of wetness with about 65F in average temperature.  This was infection risk event for downy mildew, Botrytis, Black rot, and Phomopsis.  Also, in the last two nights, the evening thunder storms brought up night time relative humidity, thus, we should keep watching out for downy mildew development.

A quick update: A series of rain event since 5/29 around Winchester area produced two Phomopsis infection events and one black rot infection events.  Two consecutive humid nights probably promoted downy mildew spore production too.  Things are still wet, thus I will update the length of wetness once things dry out.