Potato Extension


Andy Robinson

Potato Extension Agronomist


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Blightline July 31, 2013

Late blight has still not been reported in North Dakota, Minnesota or Manitoba. All late blight of potatoes and tomatoes reported this year are east of the Mississippi River, including Wisconsin, Michigan, New York and Maine. Our cool weather has resulted in morning dews that favor late blight infection, and our late blight severity values increased slightly at almost all locations the past two days. The non-irrigated stations that have reached the late blight threshold severity value of 15 are: Ada, Cando, Eldred, Humboldt, Perley, Rolla, Sabin and Warren. The irrigated stations that have reached the late blight threshold value of 15 are: Beach, Hofflund, Inkster, Karlsruhe, Leonard, Linton, Michigan, Minot, Oakes and Robinson. We recommend application of the first protectant fungicide when late blight threshold severity value of 15 occurs, just prior to row closure, or if late blight is found in your area, whichever occurs first. Because of the low late pressure fungicide application intervals can be extended to 10-12 days.
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