Tuesday, May 21, 2013
Valdensinia leaf spot (caused by Valdensinia heterodoxa) causes early leaf drop in lowbush blueberries and in prune fields can cause complete leaf drop so that no flower buds are produced by infected stems. By June 2009, Valdensinia leaf spot had caused complete defoliation in approximately 40 crop and prune fields in Nova Scotia, and had been found in Quebec and New Brunswick fields. By July 15th 2009, this fungus had been found in Maine wild blueberry fields and garden plantings. (Photo by Seanna Annis, Associate Professor of Mycology, School of Biology and Ecology)
TRESCOTT — 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.
And in this case, ''yes'' was no good. 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 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 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 year.
With the excessive rain this year, the blueberry crop was expected to be 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 the fungus will damage many fields this year, and 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 remain perfectly healthy, but those fields must be burned in order to halt the spread of the fungus to 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 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,'' she said.
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.
Valdensinia leaf spot already had caused complete defoliation throughout fields in Nova Scotia by June, and later was found in Quebec and New Brunswick.
Annis said the spots are typically large and brown and can have a bull's-eye appearance.
The fungus requires about six to eight hours of rain or fog for the spores to infect new leaves. She said the spores are heavy and can't 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.