Late blight has been found in potato fields in western Minnesota and North Dakota's Walsh County, the state's leading potato producer.
The highly contagious fungus, which caused the disastrous Irish potato famine in the 1840s, can hurt both yields and quality.
However, modern fungicides "help growers manage this disease and grow profitable crops," says Eric Tedford, a fungicide technical brand manager with Syngenta in Greensboro, N.C.
Syngenta Crop Protection sponsors the North Dakota State University Blightline, a hotline that collects local weather data to forecast the occurrence and spread of late blight in eastern North Dakota and western Minnesota.
The Northern Plains Potato Growers Association reported in its weekly update July 26 that late blight has been found in west central and southern Minnesota, as well as in Walsh County.
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Scout fields
The NDSU Blightline encourages potato growers to scout their fields and to apply fungicides on a five-day schedule in potato fields grown under irrigation and a five- to seven-day day schedule in nonirrigated fields.
"Now is not a good time to attempt to minimize production costs by limiting fungicide applications," the Blightline says.
Growers are asked to submit samples of late blight and report new occurrences as soon as possible to NDSU.
Traditionally, late blight has been rare in the region. But cool, wet conditions in recent years have allowed the disease to pop up in 2009, 2010 and again this year.
Late blight arrived early in the 2010 growing season and was relatively widespread, but turned out not to be serious, according to information from North Dakota State University.
'Disease triangle'
Tedford notes that the so-called "disease triangle" consists of three factors: a susceptible host, the presence of pathogens and a conductive environment.
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If one of more of the factors isn't present, disease doesn't occur. If all three factors are present -- as is the case in eastern North Dakota and western Minnesota potato fields -- disease can occur, he says.
Late blight spreads very rapidly and can devastate fields if control measures aren't taken, Tedford says.
More information on the NDSU Blightline: Call the toll-free hot line at 888-482-7286. Or go to www.ndawn.
ndsu.nodak.edu. Click on "applications" on the left-hand side and then click again on the "potatoes" drop-down box.
