Potato Disease Advisory #21 – July 23, 2009

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

Disease Severity Value (DSV) Accumulation as of July 22, 2009 is as follows:

Location: Shadybrook Farms, Little Creek, DE in Kent County.
Greenrow: May 1

  LATE  BLIGHT EARLY BLIGHT
Date Daily DSV Total DSV Spray Recs Accumulated P-days*
7/1 2 114 10-day interval 519
7/2 1 115 10-day interval 528
7/3-7/5 0 115 10-day interval 555
7/6-7/8 0 115 10-day interval 581
7/9-7/12 0 115 10-day interval 616
7/13-7/15 0 115 10-day interval 641
7/16 0 115 10-day interval 647
7/17-7/18 2 117 10-day interval 662
7/19-7/20 1 118 10-day interval 680
7/21 2 120 7-day interval 690
7/22 0 120 7-day interval 698

There have been no new late blight reports on potato in the region. A backyard tomato sample from the Ellendale vicinity was diagnosed on Wed. July 22 with late blight. This is the first report of late blight on tomato in DE.

Current conditions here are favorable again for late blight on tomato. The favorable weather of the last few days will continue to provide favorable weather for late blight especially if thundershowers materialize. Most potatoes will be, or are, close to maturity so they are not particularly at risk at the present time.

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