Powdery Mildew in wild blueberries in Maine is NOT a new disease
“New” powdery mildew reports
There are reports in the news of a “new” powdery mildew fungus (Erysiphe vaccinii) that is attacking blueberries around the world. The major interest in this fungus is because it has spread to countries that have recently started planting cultivated blueberries, such as China, Morocco, Peru, and Mexico. This disease is causing an increase in their production costs due to the use of fungicides to control this disease. This “new” powdery mildew probably originated from the Northeast since it is very similar to types found in our fields and Massachusetts. The fungus spread from North America to new locations probably through infected plants. A similar fungus that occurs in North Carolina’s blueberry breeding facility occurs as the “new” fungus in these other countries.
Powdery mildew in Maine wild blueberries
Powdery mildew has been a minor pathogen in wild blueberries in Maine. Powdery mildews can weaken plants, but not kill them, and decrease yields by using sugars the plant produces that the plant could be using to make fruit. This fungus is found in almost all fields in Maine but seems to cause very little damage to the plant. Wild blueberry fields have more tolerance to infection by powdery mildew than most rabbiteye and highbush blueberry varieties. Most cultivated blueberries are bred for yield characters and rarely for disease resistance. Cultivated blueberries also are typically planted with only one or few varieties in a field. If a cultivated blueberry variety is susceptible to the fungus, it can spread rapidly and affect many plants or all of the plants in a field. Wild blueberries are resistant to powdery mildew damage because of their high genetic diversity which can produce a wide diversity in susceptibility and resistance. This results in situations where one clone may be badly infected bust most of those around it will have a different level of resistance. Another factor is that powdery mildew evolved with blueberries in the Northeast and so wild blueberries have likely evolved more resistance to this disease.
If you have any questions feel free to contact Dr. Seanna Annis at sannis@maine.edu or at 207-581-2621.