Late blight arrives again in Manitoba potato country

Manitoba’s agriculture department has again confirmed findings of late blight, a highly destructive Prairie potato disease, in the central potato-producing area of the province.

Late blight is able to attack both tubers and foliage at any stage of development and can destroy entire fields if left unchecked, the province has said previously.

Suspect leaf samples submitted by an agronomist had leaf spots typical of late blight, and microscopic examination showed sporangial production in those spots, provincial plant pathologist Vikram Bisht said in a notice Thursday on the Manitoba Potato Weather Network website.

“A visit to the field showed scattered infection within the field and some low-lying areas with more infected plants,” Bisht wrote. “Another field across the road also showed scattered infected plants.”

Thunderstorms last week may have brought in the inoculum, Bisht wrote. Rains have increased weekly accumulated disease severity values (DSVs), which in turn has put the province’s potato country at medium to high risk for late blight, especially in southern and western areas, he added.

“It is very important now to rigorously scout for late blight, especially in wind-protected and low-lying areas of the fields,” he wrote. “It is also important for the tomato growers, especially home gardeners, to be scouting for late blight. A few days with disease and no fungicide can devastate the tomato plants.”

Field scouting should be concentrated in areas of a field most likely to have high moisture, dew or relative humidity for the greatest length of time, or in areas that are difficult to access with sprayer equipment.

Early symptoms are small, light to dark green, circular- to irregular-shaped, water-soaked spots. These lesions usually appear first on the lower leaves and often begin to develop near leaf tips or edges, where dew is retained the longest. During cool, moist weather, these lesions expand rapidly into large, dark brown or black lesions, often appearing greasy.

For more details from Dr. Bisht on fungicide use to prevent late blight from spreading, check out his article HERE. For more from Manitoba’s provincial ag department on scouting and control, click HERE.

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