COOL AND WET WEATHER NEXT WEEK FOR WASHINGTON AND OREGON

Forecast conditions favorable for the development of bunch rot

Dr. Gary Grove, Professor of Plant Pathology, 509-786-9283
Dr. Michelle Moyer, Assistant Professor/Extension Viticulturist, 509-786-9234

Date: Thu, Sep 29, 2011 at 10:37 AM

Colleagues:
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,

Gary Grove and Michelle Moyer Washington State University
Dr. Gary Grove Professor of Plant Pathology Washington State University Irrigated Agriculture Research and Extension Center 24106 N. Bunn Road Prosser, WA USA 99350 509-786-9283 grove@wsu.edu

Washington State University