**This update is a compilation of a series of emails sent between 29 and 30 Sept 2011 regarding the 2011 vintage.**
Disease Update- Botrytis Bunch Rot Alert
By Gary Grove and Michelle Moyer
First, the good news: Gerrit Hoogenboom and the AgWeatherNet team have posted a preliminary version of the Broome Botrytis Bunch Rot model on the AWN web site (http://weather.wsu.edu). Once you are logged in, click on “AWN Models” in the vertical blue menubar and then “Grape Bunch Rot”. Users will need to select station locations and date span (we suggest bloom through the current day) and then bloom date again. As we are in the midst of Botrytis season there is little time for formal training so we have attached a sample model output from AWN. The “Site Summary” output includes the bloom date (entered by client), last date of moderate to high infection risk, a choice to look at season-long conditions, and a risk index graph. Available but not shown is also a table of some fungicides registered for bunch rot management. Unfortunately, at this time we know little of the postinfective activity of these compounds so we cannot recommend treatment in response to an infection event; the best approach is to apply these compounds protectively BEFORE an infection event. Given the news below, it might be a busy several days ahead.
Now the bad news: Hopefully you’ve all seen the weather forecast for the following 10 days. The forecasts are that conditions very favorable for the development of bunch rot:
116 PM PDT WED SEP 28 2011
…COOL AND WET WEATHER NEXT WEEK FOR WASHINGTON AND OREGON…
THE WEATHER WILL BE CHANGING EARLY NEXT WEEK TO A COOLER AND WETTER
PATTERN. A SERIES OF FRONTS WILL BE MOVING ACROSS THE REGION WITH
PERIODS OF RAIN. THE FIRST SYSTEM WILL BE MOVING THROUGH ON MONDAY
WITH A STRONGER ONE TUESDAY INTO WEDNESDAY. RAINFALL AMOUNTS
THROUGH WEDNESDAY COULD BE UP TO ONE INCH AT THE LOWER
ELEVATIONS…WITH 1 TO 2 INCHES IN THE MOUNTAINS. HIGH TEMPERATURES
WILL BE IN THE 50S AND 60S WITH OVERNIGHT LOWS IN THE 30S AND 40S.
SOME SNOW IS POSSIBLE IN THE HIGHER MOUNTAINS.
We will be updating this information regularly on the WSU Viticulture and Enology Facebook page.
Best wishes and good luck!
Enology Notes – Grape Ripening
By Thomas Henick-Kling and Jim Harbertson
Grape flavor and acidity
The wonderful ripening weather we have had has allowed some very nice flavors to develop in most white grapes and in several reds. It appears that we are ahead of 2010 in terms of flavor ripeness and we also have lower acidity in many vineyards. In many white grapes the titratable acidity is already below 10 g/L and the pH above 3.0. These are acid ranges that can very easily managed with malolactic fermentation and perhaps a small chemical deacidification – lowering final TA by perhaps 0.5 or 1 g/L. If you see larger deacidifications needed then it is better to do this in the juice prior to fermentation. For help with deacidification, please refer to our article last October.
It seems though that acid management will not be a problem this year – or an easy one to handle. Unfortunately our soluble solids is still lagging behind. Yet, this is not a problem, sugar adjustments are easily made (best with neutral tasting cane sugar). When chaptalizing, it is not a good idea (and in some cases illegal) to increase the natural alcohol content by more than 2% (v/v). Remember that 20 Brix equals 20g/100 g of liquid, or 200g/L. To chaptalize from 20 Brix to 22 Brix you would add 20 g of sugar per liter of must. When chaptalizing, remember to first solubilize the sugar first in must or water and allow space in your fermentation tank for the increase in volume. A good practice is to make a 200 Brix (2000 g/L) solution and add this solution back to increase the fermentable sugar content. At 59°F you can dissolve up to 1.97 kg of dry sugar in 1 liter of water or wine. At 86°F you can dissolve up to 2.19 kg sugar per liter. Remember to add the sugar under constant stirring, making sure it is all dissolved before adding the sugar solution to the must.
Botrytis bunch rot threat
Remember also that if you are going to use a fungicide that yeast are actually fungi, so following preharvest intervals are not only a legal requirement, but also a good idea for a healthy fermentation. Clarify white musts well, as it will help to remove any spray residue. Should you run into fermentation difficulty and you suspect spray residue as a cause, try using yeast hulls. The yeast hulls (cell walls and membranes) bind a range of inhibitors such as fungicides (copper included).
Always remember to add yeast nutrients! Aim for 250 mg/L Yeast Available Nitrogen.