Virginia Grape Disease Updates

As of 3/29/12, about 20% of our Chardonnay buds and shoots are showing the injuries from the frost event on 3/27/12.  Damages on Merlot is about 5%.  I hope your vines are OK.

I guess both Anton and I tend to work on Sundays...  He send me two nice pictures of flag shoots. and As you can see leaf surface is covered with white powder (= mycelium and spores of powdery mildew). He also mentioned that he has used Armicarb and sulfur together and did not see any phytotoxicity.  Thus, if your intention is to fight against established colonies (whether flag shoots or late in the season), it would be a good combination.  If Armicarb or Kaligreen is too expensive for your budget, a straight sulfur application is the alternative. The other thing about powdery mildew is the effect of cold temperature.  According to a recent study by Cornell, low temperature (8 hr of below 8C or 46F) stops the powdery mildew activities. This is another reasons why we do not see much activity of powdery mildew relatively early in the season.  Hopefully, we have enough cold (but not freezing) nights ahead of us to stop early season powdery mildew.

In reply to the previous post about powdery mildew, Anton (Baudoin of VT) made a very good comment about "flag shoots" of powdery mildew.  This is a case of infection where powdery mildew pathogen survives on buds, and infect developing shoots from the get-go.  The result is infected shoots with retarded growth, hence people call it flag shoots.   You can see a picture from this Australian department of Ag site. Why this is important? Since it bypasses the ascospore stage, the infection event I mentioned in the previous post will be irrelevant, and you will have conidia in your vineyard from the beginning of the season, i.e., mass production of spores can happen quickly. Based on conversations I have had with growers in VA, flag shoots do not occur in VA growing conditions, and I have not seen this symptom yet.  This is primarily due to low winter temperatures; however, the winter we had was very mild, plus we had a dry summer (before Irene) to promote powdery mildew in 2

Well, it typically won't happen until May or so, but under this weather conditions, you cannot expect the usual trend.  Often time, powdery mildew is common under dry weather because powdery mildew conidia, which are primary spores during summer time, do not require water for infection.  However, ascospores, which are initial inoculums (spores), require water.  More than 1 inch of rain followed by 13 hours of leaf wetness with an average temperature range of 50-80F is required for powdery mildew ascospore infection.  Winchester area received rain starting from 9:15am today, we are having pretty much continuous rain (and it's still going), and the average temperature (at this point) is about 60F; therefore, it counts as an infection event. If your vines already broke buds, the new growth are susceptible for infection.  Please monitor leaves for powdery mildew to see if it was indeed an infection event for you.  It typically takes about 7-10 days for disease development.

Our 4-yr old Chardonnay was about 10% bud break yesterday (the 21st) morning.  Our 4-yr old Merlot was <5% bud break. Older vines are still holding off. Well, the season has been officially started whether I am ready or not! Also, I updated the season template based on comments from users.  If you have any comments or suggestions, please let me know.

Thanks for those of you attended our first annual grape IPM workshops!  The number of attendee was about 110 people! I am still working on the 2012 version of the workbook, and I will publish it by the end of this week.  In the meantime, I would like to share the fungicide planning template for 2012 season, which is a part of the workbook.  Please visit this link (Google Doc, no sign-in required). I won't let you edit on-line; however, you can download it as Excel file.  (I am hoping that we can come up with on-line edit option.  We will see...)  If you prefer to download Excel file directly, please let me know.

Two weeks of 80's and 70's surely moved things forward.  When I checked our Chardonnay buds last week, it was swelling, but was still tight, but now it looks like they are ready to go at any moment. (Note: these are 4-yr old young vines.  Also, sorry for out of focus pictures.  I forgot to take my camera with me yesterday.) Hopefully, it will go well with a longer than usual growing season, and we end up having early harvest this year!! The first disease to be concerned is, as usual, Phomopsis.  The best management strategy against Phomopsis is use of a protective fungicide such as mancozeb or captan, since we do not have any material with curative activity. Also, since we had a warm dry early summer before Irene, many of us saw quite a bit of powdery mildew.  Chances are, we have a plenty of inoculum.  Although we do not typically see powdery mildew until later in the season, with this warm winter, I am not sure what will happen.  I know it is not the best IPM practice,