Potato Disease Advisory – May 21, 2009

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

Late Blight Advisory
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
5/14 1 45 10-day spray interval
5/15 3 48 10-day spray interval
5/16 2 50  7-day spray interval
5/16- 5/20 0 50  7-day spray interval

Fungicide sprays are recommended if no applications have been made this season. 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 Delaware Commercial Vegetable Production 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.

Please note: I have reversed my decision to use Blightcast from Skybit to predict late blight. I have used Wisdom in the past and all my original data calibration for predicting late blight was done with Wisdom, and it has worked as best as I know, so I will continue with it this season as well. Sorry for any confusion this may have caused. You may notice that the DSVs are higher which is due to the way that Wisdom calculates these values compared to other programs.

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