Skip to main content

Note on sour rot


As the harvest approaches (plus recent rain events in some part of VA), I am receiving several emails on sour rot.  It is often confused, but not all late season rots are sour rot.  Sour rot is basically a disease caused by bacteria that form acetic acid, such as Acetobactor and Gluconobactor.  It is often associated with wounds (birds, insects, hail, too much rain, early season powdery mildew, certain very fair-skin varieties, etc), high Brix level (13-15 or higher), warm temperature range (high 60F to mid 70F).

Since these bacteria cannot penetrate berry skin tissues by themselves, what we typically recommend is wound management (e.g., bird netting, grape berry moth management, etc.), and many people mention that it works.  However, with a potential role of Spotted Wing Drosophila (or lesser extent, African fig fly), which may able to penetrate skin, there is a possibility that we may see more sour rot in the future. 

Luckily, Dr. Wayne Wilcox's group at Cornell University has been working to see if we can combine an insecticide and copper (they also tested potassium metabisulfite, or KMS, but please note that KMS is not legal to be used in the vineyard in the US + very toxic when you get it on your eyes or inhale it).  A good news is that it looks like a combination of copper + Delegate provided as good protection as KMS treatments.  Although the report is not really concerned about spotted wing Drosophila, the combination of an insecticide and copper resulted in ~50% control of sour rot.  If you are interested in his work, here is Dr. Wayne Wilcox's report on sour rot.  Please note that as Wayne indicates in the report, it is based on only one year of data, we need to see whether they can repeat the results in 2014.  Also, they intentionally sprayed with 7-day schedule, and it maybe an overkill to spray every 7-days at the end of the season.  (They mentioned about lowering the frequency once they prove that the treatment works.)

Also, the experiment is based on the case where you do not have wounds to begin with.  If you have already seen wounds on berries, I am not sure how effective the treatment would be.  Since fruit flies tend to be attracted to open berries, I would think it works too, but that something we need to investigate.

Although copper has 0-day PHI, it has potential residue issue that may affect fermentation process.  However, as I mentioned in the last post, sometimes it may come down to whether you will have a crop or not, and at that point, having an option certainly helps. 

Lastly, based on a few trials we conducted, we noticed a trend with a better powdery mildew management at bloom time resulted in lower Botrytis and sour rot.  Thus, if you have a variety that is very prone to sour rot issue, make sure to have a very good control on powdery mildew too.




Comments

Popular posts from this blog

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 ga

Season's Greetings!

I hope you and your family have a good holiday season and a Happy (and safe) New Year! Thanks again for your support of our programs. Here are some recent media highlights. 😉 The link will open a new window. AHS AREC promotional video  that highlights some of our activities. The link did not work... It asks you to log in to VT. I will request the IT people to change the setting, but in a meantime, here's the same video. We also appeared in  the Library of Congress project “Winery Workers of Virginia”. One more announcement: I will be moving this blog to a new location ( ext.grapepathology.org ) early next year. I had to make a change due to the email subscription service, which has been terminated.  You do not need to change your bookmark or your email subscription. The URL will be forwarded to a new site and your email subscription has been moved to a new site already. 

Recent downy mildew risk events

 It seems that several rain events have happened over the course of the past two weeks or so. Here is a summary of recent downy mildew risk events, based on the NEWA stations and DMCast. Bristol, VA Fifteen days with potential DM infection event(s) since Sept 1. The latest event happened last Sunday. Floyd, VA Eleven days with potential DM infection event(s) since Sept 1. The last event happened last Friday. Charles City, VA Twelve days with potential DM infection event(s) since Sept 1. The latest event happened yesterday. Central VA Since there was a wide variation among stations, I am listing several around Central VA. Tyro, VA Nine days with potential DM infection event(s) since Sept 1. The latest event happened yesterday. Red Hill and Crozet, VA Only one day with potential DM infection event(s) since Sept 1. Olympic Lake Thirteen days with potential DM infection event(s) since Sept 1. The latest event happened last Sunday. Washington, VA Eight days with potential DM infection event