Mummy berry is not a seasonal breakfast cereal. Instead, it is a fungal disease of blueberries.
This particular fungal disease is caused by the Monilinia vaccinii-corymbosi fungus. It is nearly always present in the soil, but a cool, wet spring can set the stage for serious losses.
Symptoms of mummy berry
A healthy summer blueberry bush is thick with leaves and twigs, blossoms and fruit. After a cool, wet spring, however, you may notice that some of the blueberries shrivel up, turning hard and grey. Before the fruit even appears, you may see a coating of brown or blue spores on the veins of infected leaves. You may also see drooping, wilting, brownish flower clusters that are turned in on themselves, before they turn brown and die. Immature fruit falls to the ground and twig tips become blighted in a condition called ‘shoot strikes’ and die. This is mummy berry.
The mummy berry mushroom spews fungal spores into the air, which then land on all this tender new plant tissue. Spores are also carried by pollinators, such as honey bees, wind, and water. Once the fungi reach your blueberries, they need adequate moisture to continue growing. According to research from Ag Canada, the following chart tells you the likelihood of infection at different temperatures, depending on how long leaves stay wet:
If you cut open an infected green berry, you can see white fungal tissue. [Afterwards, be sure to clean your cutting tools with a solution of one part bleach and nine parts water; or, you can spray your tools with disinfecting bathroom cleaner. If you don’t, you will spread the infection.]
Controlling mummy berry
Once infection occurs, all you can do is removed the diseased tissue and either burn it or throw it in the trash. You can reduce the chance of mummy berry causing too much damage in your garden with these tips:
Resistant blueberry varieties
Some blueberry varieties are more resistant to mummy berry than others. According to the USDA Agricultural Research Service, low bush varieties with less than 3% mummified berries include:
However, high bush varietals are generally not recommended for the Bay Area. They need more chill hours than we tend to get. There is also a cross between a southern highbush and rabbiteye blueberry, called 'Pearl River’, that is resistant to mummy berry. The ‘Berkeley’ variety seems to be the most vulnerable to mummy berry infection.
To enjoy the lush, sweet flavor of blueberries in summer, be sure to monitor your plants for signs of mummy berry!
You can grow a surprising amount of food in your own yard. Ask me how!