The late blight fungus has been confirmed in several North Dakota potato fields.


There are also unconfirmed reports in Manitoba, Canada.


No case has yet been confirmed in Minnesota, said Chuck Gunnerson, interim president of the Northern Plains Potato Growers Association, East Grand Forks, Minn.


“It’s a very serious deal,” Gunnerson said. “We’ve had other states that have dealt with the problem. It started on the East Coast — New York, Maine, Michigan, Wisconsin, even Washington state had some, I think.”


The source of late blight is unknown, Gunnerson said. The fungus is driven by cool, wet weather, which has been persistent in North Dakota in early-to-mid August. The fungus starts as a bullseye-like lesion on potato plants leaves. The cool and wet conditions cause spores to form and spread from plant to plant across fields. Rain water can wash spores off one plant and move through soil to infect tubers of other plants. Tubers then decay within a few days.


Late blight has been confirmed in a field in Grand Forks County and a field on the North Dakota/South Dakota border.


“A number of growers have been on a preventative measures program all summer, and they believe their fields are safe,” Gunnerson said. “Those growers who have lagged behind in fungicide application have a real concern.”


The association recommends all potato growers in the area do four things:



  • Apply fungicide to fields as soon as possible.
  • Scout fields for late blight, especially low areas with high moisture.
  • Kill late blight hot spots immediately with a chemical desiccant. All infected fields should be vine-killed before harvest.
  • Consider applying a phosphorous acid fungicide to potatoes going into storage.

Gunnerson said 10-12 million bags of potatoes were lost in storage in 1999 because of late blight infection, costing the industry about $150 million.


Growers can send suspected late blight samples to North Dakota State at NDSU Department 7660, Box 6050, Fargo, N.D., 58108.


“We’re just finding out about this in the last couple days,” Gunnerson said Aug. 21. “Growers are responding quickly by going into fields and scouting them and then, if they find any, putting a dessicant on it to destroy the vines. Cooperation from growers has been very good thus far.”


 Correction note: The original story contained an incorrect word in this quote: “A number of growers have been on a preventative measures program all summer, and they believe their fields are safe,” Gunnerson said. “Those growers who have lagged behind in fungicide application have a real concern.”