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Black dot disease detected in P.E.I. potato crops

A fungal disease that affects plant tissues has been detected in Prince Edward Island potato crops.

'Not a doom-and-gloom sort of situation,' says researcher

Gwyneth Egan · CBC News ·
A man on his knees gathers up potatoes from a red dirt field.
Black dot isn't thought to be widespread on the Island, but growers are keeping an eye out for it, says the P.E.I. Potato Board. (Aaron Adetuyi/CBC)

A fungal disease that affects plant tissues has been detected in Prince Edward Island potato crops.

Black dot disease — named for the fine black spots that appear on infected roots, stems and leaves — is typically brought in on infected seed and spreads through soil, said Julie Pasche, associate professor and chair of potato pathology at North Dakota State University. 

Pashe said that once the pathogen is in a field it will remain in the field for quite some time and build up with each additional potato crop.

"They are very durable structures that survive in the soil," she said. "They're not broken down very easily."

Black dot isn't thought to be widespread on the Island, but growers are keeping an eye out for it, said the P.E.I. Potato Board. 

Pasche ran a session on the emergence of black dot at the P.E.I. Potato Conference earlier this month. 

What are the effects?

There are two phases of black dot: the foliar phase and the tuber blemish phase, Pasche said. 

The foliar phase "really ties in with the early-die complex," which is also caused by other diseases like verticillium wilt.

That could result in yield loss and smaller tubers, which would affect processing growers, she said. 

Cavendish and McCain branded potato products are pictured in green and red bags on the shelf at a grocery store.
The foliar phase of black dot would affect processing growers more, while the tuber blemish phase would have a greater impact on fresh table stock growers, says Pasche. (Ben Nelms/CBC)

The second phase is especially important for fresh table stock growers, Pasche said. That phase causes discolouration.

"If you're in the grocery store, [they] wouldn't necessarily be the ones that you would choose." 

Management strategies

Black dot can be seen with the naked eye, but it can sometimes be difficult to spot.

Diseased potatoes
'The most important thing is to be able to discern the symptoms and signs of black dot,' says Pasche. (Sam Farley/CBC)

It can look very similar to other diseases, Pasche said. "The most important thing is to be able to discern the symptoms and signs of black dot." 

When it comes to eliminating the disease, Pasche said the best method is to let land lie fallow for 15 to 20 years, depending on how much of the pathogen is in the soil. 

Some fungicides can also be "somewhat effective," she said. 

A tractor pulls a machine through a potato field.
The best way to eliminate black dot is to let land lie fallow for many years, says Pasche. (Shane Hennessey/CBC)

Black dot disease is relatively widespread in the U.S., and growers are managing it "to a greater or lesser degree," Pasche said. 

Improvements to management strategies are needed, but "it's not a doom-and-gloom sort of situation," she said.

ABOUT THE AUTHOR

Gwyneth Egan

Gwyneth Egan is a digital writer at CBC Prince Edward Island. She is a graduate of Carleton University's master of journalism program and previously interned with White Coat, Black Art. You can reach her at [email protected]

    With files from Jackie Sharkey

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