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Maine’s Wild Blueberry Crop Imperiled by Leaf Spot Fungus

July 28, 2009 - TRESCOTT -- With fog swirling around her, Seanna Annis, a blueberry pathologist at the University of Maine, scanned the low bushes along a gravel road through the blueberry fields Sunday evening. She stopped, brought out a magnifying lens and pinched a leaf from a plant.

“Yes,” she said, seconds after examining the spotted leaf.

With that, the farmer knew his field was lost. Even though the plants are lush with fat blueberries just days from harvest, they must be burned.

In this field and six others in Maine, Annis has identified Valdensinia leaf spot, a deadly fungus that spreads easily and quickly in damp weather. The fungus causes leaves to drop off the plant and interrupts the normal cycle of bud set for the next season.

“I’m extremely worried, very, very worried,” Annis said Monday. “This could really be devastating.”

The disease, which thrives in wet, damp conditions, migrated to Maine from Nova Scotia, New Brunswick and Quebec, and as bad as its effects could be on this year’s harvest, Annis said it could be even worse next season.

With the excessive rain this year, the blueberry crop was one of Maine agriculture’s bright spots. Farmers and producers at a recent Wild Blueberry Field Day in Jonesboro predicted a bumper crop.

Annis said that not only will the fungus damage many fields this year, if it goes undetected in larger barrens, it could destroy the crop next year.

There is no fungicide available for eradication, she said. “The only way to destroy the fungus is to burn it,” she said.

Annis said the blueberries are unaffected and are OK to eat but those fields must be burned to halt the spread of the fungus to other, healthy fields.

“When it is wet, like it has been, this spreads like wildfire,” she said. “Because it attacks all the young leaves, the plant puts all its energy into producing leaves and has none left to produce blossoms or berries. You could end up with fields that look like sticks.”

Any fields that are producing blueberries this year will be pruned or mowed next year, Annis said. “The fungus will survive over the winter in infected leaves, and just about the time the plants bloom in the spring, it will infect during the first three days of wet weather.”

Before this past weekend, Annis had found Valdensinia leaf spot in fields in Jonesport, Township 24 and Sumner. She found it in four more places Sunday.

“I am surprised at how much I’m finding,” she said.

Valdensinia leaf spot already had caused complete defoliation throughout fields in Nova Scotia by June and later was found in Quebec and New Brunswick fields.

She said she is particularly concerned because none of the larger growers has contacted her about the disease.

“It’s been the smaller growers that have really looked at their plants,” she said. “If there is a harvest, it will be spread. What may be a small patch of infected plants this year will be whole fields next year.”

Annis said the leaf spots are typically round, large and brown and can have a bull’s-eye appearance. Leaves can have from one to about 10 spots, one-eighth to one-half inch and larger, but spread rapidly.

The fungus requires about six to eight hours of wet weather — rain or fog — for the spores to infect new leaves. She said the spores are large and heavy and cannot be carried by the wind.

“This means this fungus cannot move across large bare areas or roads without human [or animal] help,” Annis said. “Growers should clean dead leaves off vehicles, equipment, boxes and footwear.”

She said a single dead leaf on a tractor or the bottom of a shoe is enough to infect an entire field.

Recommended treatment includes burning the diseased area in pruned and crop fields, as well as a 10-foot edge outside the area of the infected stems.

Anyone suspecting the disease in their fields may call Annis or Dave Yarborough at the Blueberry Hotline, 800-897-0757.

By Sharon Kiley Mack
Bangor Daily News Staff , July 28, 2009


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