Wisconsin Potato and Vegetable Growers Association

Vegetable Crop Updates – Late Blight Suspected in Adams County

July 25th, 2016 | Posted in: Crop Updates, News

Late blight on potato has been visually diagnosed in Adams County today. The lesions are typical for blight including dark brown, water soaked lesions with pale green borders. However, there is little to no pathogen sporulation visually evident at this time. Using an ELISA-based immunostrip analysis, we did confirm that the disease was caused by a Phytophthora species. It is likely late blight (Phytophthora infestans), but without sporulation and further species-specific evidence, I’m not yet confirming this. My lab will be determining the species, and subsequently the genotype/strain type and will make this information public as soon as possible (tomorrow).

There is one other species of Phytophthora that can be disease-causing on potatoes and that is Phytophthora nicotianae. This species tends not to sporulate on potato plants and has been infrequently found throughout WI potato fields. The field signature for this ‘other’ Phytophothora is also a bit different than late blight – and the field visually diagnosed today is showing symptoms much more consistent with late blight.

I send out this news to urge a tightening up of preventive fungicide programs on potatoes and tomatoes in central Wisconsin. If you have not, to date, applied any late blight specific fungicides, it is an important time to get fungicides on that have some systemic (and kick back/curative) activity for more aggressive management of late blight at this time.

Click here for the late blight fungicide list for WI that includes modes of action to aid you in your selection of treatments with systemic, curative, protectant activities.

Best regards,
Amanda Gevens
Associate Professor & Extension Specialist
Potato & Vegetable Pathology
Plant Pathology Department
University of Wisconsin-Madison
Madison, WI 53706
[email protected]

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