Potato Disease Advisory – May 13, 2009

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Late Blight Advisory
If you would like a fax or email report please call (302) 831-4865, or email bobmul@udel.edu.

We are using the E-WEATHER SERVICE from SkyBit, Inc. as we have in the past. The service determines specific requested weather parameters (temperature, relative humidity and rainfall) based on calculations of data from the nearest National Weather Service stations. This weather data is used in the WISDOM software program for predicting late blight and making spray recommendations and accumulating p-days for early blight forecasting. Our location this year is:
Location: Shadybrook Farms, Little Creek, DE (Kent County)
Greenrow: May 1

Date DSV Total DSV Spray Recommendation
5/3 -5/6   41  
5/7 2 43  
5/8 1 44  
5/9- 5/13 0 44 10-day spray interval

Disease severity values accumulated very quickly during the past rainy period. The threat of late blight from seed infection is low to medium, but there was some in Maine last season. Be vigilant, given this recent weather pattern. Apply sprays of mancozeb (Dithane, Manzate, Pencozeb, Manex II), Gavel or Bravo (chlorothalonil) now and then repeat before plants canopy down the row. See the 2009 Delaware Commercial Vegetable Recommendations for more information on fungicides.

Fortunately late blight has not been a problem here in Delaware for many years and unless you have seed from an unknown source the risk of late blight is low. However, the weather was perfect for it if it was present on seed.

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