Late Blight Arrives in Northern Wisconsin

Aug 15, 2013

A destructive plant fungus has been found in Langlade and Portage Counties, and could spread to other parts of Northern Wisconsin.  

Late blight can affect leaves or other parts of potato and tomato plants.
Credit Howard F. Schwartz / Colorado State University

Late blight affects tomato and potato plants. Steph Plaster is an Agriculture Agent for UW Extension Langlade County.  Plaster says check often for signs of late blight on almost any part of the plant.

“Lesions on the leaves are going to be like a gray-green to brown spot on the leaf that may look wet or oily.  And it will have a pale green border all the way around the spot. Now fruit or tubers will have kind of rusty brown spots that will be firm to the touch.”

Plaster explains preventative measures are important as you can’t reverse the spread of late blight once it starts.  The destructive fungal disease is the same one responsible for the Irish potato famine. 

“It can easily destroy an entire crop or an entire field in under three weeks.  It can attack the leaves or stems – it will kill the entire plant.”

Commercial growers can apply various chemicals to try and prevent late blight.  Home growers can choose to use copper or chlorothalonil as a preventative.  Afflicted plants should not be saved for seed or compost.  UW Extension says you can bring in samples of plants suspected to have late blight for testing.