Friday, September 30, 2016

Rain rain...

It has been pretty wet week so far. At Winchester, we observed about 11 hours of wetness on the 26th with an average temperature of 64F, 50+ hours (and counting) from the 28th to today with an average temperature of 61F. It is certainly long and warm enough for Botrytis infection.

Whether we require a fungicide application for Botrytis or not at this point depends on several potential factors. The first one, of course, is whether you had a previous application or not. If you had a previous application to cover these rain events, you probably do not need to be concerned much.

The second one is a time to harvest. If you still have several weeks to go, you may want to consider an application, but if you will harvest within a few days, I am not sure an application of fungicide will help you much since we do not have any curative materials for Botrytis. Whatever we spray at this point will be good against future infections, but not the infection happened already.

The third is cultivar. Chances are, many fruits out there at this point would be that of red cultivars, which is relatively less susceptible to Botrytis infection than whites, especially the one with a loose cluster architecture. I can see some white cultivars such as Petit Manseng can still be out there, but Petit Manseng is also less susceptible to Botrytis than many other whites.

The fourth is the environment. The rain this week was pretty severe, but the last major rain event at Winchester was 18 August. We had wetness event here and there, but these were relatively short events (many are less than 5 hours in leaf wetness), thus, I have a feeling that this dry weather did not favor spore production of Botrytis. Thus, even the environment was favoring this week, spores might not be available to cause infection. Since it has been pretty dry, the application you have made a while ago may still not be washed away too.

The other late season disease you may want to consider is sour rot. With this rain, berry skin may be damaged and that may invite sour rot pathogens to come in. Our understanding is that sour rot is caused by several different types of pathogens, thus, often time, a broad spectrum fungicide is recommended. I do not think any of fungicide works to stop the on-going infection, but you may want to stop the spread of sour rot. Something like copper or captan may be a good choice, especially if you have a few weeks to harvest. Both Switch and Fracture list Botrytis and sour rot (for suppression, not control) as a target disease. Also, polyoxin-D materials such as Ph-D or Oso list not only Botrytis, but also Alternalia, which is also known to cause late season general rot, as target pathogens.

Lastly, here is re-posting of a list of fungicide with relatively low PHI for your reference.

Wednesday, September 7, 2016

On these unusually slow ripening issues

Maybe I should keep posting that rains are coming... Each time I do, it looks like rains disappear. ;)

If you have not subscribed to the email list of Dr. Tony Wolf, who is our viticulturist, please do. It always have a wealth of information. In his latest newsletter, he explores potential reasons why some of cultivars are stalling on ripening process this year. Our Chardonnay is still stuck at 19 Brix or so too!

The below is a link to his newsletter, but it typically take several days for the newest one to appear. Thus, the best way is to subscribe to his email list (the instruction for subscription is listed on the page too).

http://www.arec.vaes.vt.edu/alson-h-smith/grapes/viticulture/extension/VN_options_index.html

Friday, September 2, 2016

List of low PHI materials for Botrytis, powdery mildew, and downy mildew

Well, I was hoping that the rest of the season would be nice and sunny, but I was little naive. Looks like some portion of VA may be affected by tropical storm Hermine. Plus, probably due to the hot several weeks with no cooling time during the night in August, some cultivars have been very slow to ripen. I was bit surprised to see our Chardonnay is still around 17 Brix this week.

Thus, I complied a list of fungicides with relatively low PHI (7 days or less). I cannot cover every single fungicides out there, but I tried to cover common ones. Please click here to download the table from Google drive.

NOAA's precipitation prediction for Harmine as of 2 Sept. 2016