Published online: Jun 10, 2010
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Forecasts in 2010 were generated using data from Parma, Twin Falls, Rupert, Aberdeen, Fort Hall and Rexburg. Based on the forecast, late blight is expected in Twin Falls, Rupert, Aberdeen and Fort Hall.
Any actual outbreak of late blight will be influenced by fungicide spray programs, presence of potential inoculum sources and weather later in the season. Our current recommendation is to plan on spraying at row closure and then continue on a 10- to 14-day schedule. This recommendation may be modified depending on subsequent weather patterns. 
A useful discussion of fungicides effective against late blight can be found at following link:

Source of Inoculum
The evidence indicates that the late blight outbreak in southern Idaho in 2009 came from diseased tomatoes. We also have evidence that this may have happened in western Idaho in 2005. In 2009, a severe outbreak of late blight in the Northeast U.S. was linked to transplanted diseased tomatoes. If you are buying tomato transplants from a garden center in your area, keep an eye out for sick-looking plants. If you find any suspicious lesions, please contact us or an extension specialist from the University of Idaho for confirmation of late blight.

Dr. Phillip Wharton of the UI has authored a publication on the impact of tomatoes with respect to potato late blight. For more information on late blight in Idaho you can call the UI late blight hotline at (800) 791-7195. Or for instant updates on the status of late blight and other diseases in the state you can sign up for SMS text message notifications by texting "follow potatodiseases" to 40404.
Late blight was only confirmed in one area in southern Idaho last year. There are no cull piles or any apparent overwintering sources for the pathogen in the 2009 affected area. Potato seed can also be a source.