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Late blight on potatoes

More late blight information

Large leaf spots (lesions) are common with late blight. These were the main symptom seen in a commercial field on LI in 2009 when this disease was first found. The white growth on the leaf underside (see arrows, image below) contains hundreds of spores of the pathogen that could be dispersed by wind to other leaves in this field or beyond.

potato leaf blight

Upper leaf surface with late blight lesions (below)

potato leaf blight

Spores of the pathogen are visible on the lower (under) surface of leaves (below)

potato leaf blight

Close up of spores (below)

potato leaf blight

Leaf lesions can be small when they first start to develop (below left).

potato leaf blight

Symptoms also occur on other parts of potato plants including stems, petioles, and flowers. Following two photographs were taken on LI in 2006. White growth contains a lot of spores.

potato leaf blight

potato leaf blight

When first symptoms are mostly on stems (next two pictures below), it can be difficult to detect the onset of late blight, especially in a large planting as on a farm. All plant tissue above stem lesions will die shortly because the stem is completely affected, which is one reason that late blight is so devastating.

potato leaf blight

potato leaf blight

Below: tuber blight (Photo courtesy Dr. Steve Johnson, University of Maine Cooperative Extension.)

late blight on potato tuber

Below: tuber blight (Photo courtesy Dr. Steve Johnson, University of Maine Cooperative Extension.)

late blight on potato tuber

Below: tuber blight (Photo courtesy Dr. Steve Johnson, University of Maine Cooperative Extension.)

late blight on potato tuber

Below: tuber blight (Photo courtesy Dr. Steve Johnson, University of Maine Cooperative Extension.)

late blight on potato tuber


More late blight information:

2014 updates:

2013 updates:

2012 updates:

Late blight brochures for gardeners:

2011 updates:

2010 updates:

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