While Sclerotina Berry Drop is a relatively new disease impacting the blueberry crop, a scientist who helped identify the fungus suspects it has been lurking in the shadows for some time.
Dr. John Sutton is a plant health consultant based in Ontario, who has been conducting field trials in PEI since 2010. Right from the beginning, he noticed there were black dots about the size of a pinhead on the flowers, berries and leaves. For the first two years, he said they essentially ignored the spots but then they decided to look into the matter further.
He brought the Island industry up to date on his research during a blueberry information day held recently at Red Shores. Dr. Sutton said the laboratory research indicated the dots, called sclerotia, are the same strain that causes typical symptoms of white mould disease on sunflowers and carrot roots.
“The unusually small size of the sclerotia that formed on blueberry flowers berries and leaves was presumably related to limited availability of food to support growth of the fungus,” he said.
Dr. Sutton said the obvious question is how can the disease cause considerable losses while going largely undetected. He said the answer lies in the fact the flowers, berries and leaves that become infected by Sclerotinia usually fall to the ground without having first shown any obvious symptoms or signs of disease.
“The fallen tissues become obscured and lost among the crop residues accumulating on the soil,” he said. “At the same time, sufficient normal-looking flowers, berries and leaves remain on the plants that no suspicion of anything being amiss may be raised during field inspections.”
He said the losses from the disease are likely equal to other major blueberry diseases like mummyberry, phomopsis canker and botrytis grey mould. The guest speaker said the proportion of berries infected by Sclerotinia tends to decline as the season goes on. Samples taken during the last growing season showed 20 to 40% of berries taken from the plants in mid July were infected by Sclerotinia. However, very few infected berries were encountered in August, and no infected berries were found in samples of the harvested crop.
Dr. Sutton said the Island research is consistent with work done in Quebec and Northern Ontario on high bush blueberries. He explained “there is little doubt that most or all berries infected by Sclerotinia dropped off in the field. Hence we have come to call the disease “Sclerotinia berry drop”
He said there are no products on the market to control the disease. However, he said their research has indicated EndoLeaf does offer some control.