Mummyberry, a Devastating Disease of Blueberries
If you grow blueberries, look out for mummyberry, which can wipe out your crop if untreated
If you're thinking about planting blueberries in your garden, or if you already have, you need to keep a close eye out for a blueberry disease called mummyberry. Not only can it kill your entire crop, it can come back next year and kill that crop, too.
The Disease Itself
A fungus called Monilinia vaccinii-corymbosi causes mummyberry. The fungus has an odd etiology. It spreads through windborne spores in the first year, and overwinters thereafter in "fruit mummies" on the ground.
A fruit mummy is basically what it sounds like: a tough, shriveled fruit remnant that's all that remains after infection.
As buds open in the early spring, little fruiting cups called apothecia emerge from the fruit mummies and spit spores into the air, re-infecting the blueberry bush.
The first spores infect new leaves and shoots, causing them to wither and die. This is the primary infection. This infection eventually releases new spores, which blights the flower clusters as they open in a more-damaging secondary infection.
As the infect fruit starts to develop, it turns pinkish to light brown; and as it matures, it begins to shrivel up. Eventually, the berry becomes hard and white, and falls to the ground to form a new fruit mummy.
Your first line of defense against mummyberry is the application of an appropriate fungicide to your blueberry bushes early in the spring, preferably at the green bud stage.
If you notice any infected plant material later on, you should immediately cut it off, pruning as deeply as necessary to remove the infection, and destroy the infected material. Next, very closely look for the fruiting cups on the ground under your bushes.
They'll actually look like little chalices emerging from withered berries, the aforementioned fruit mummies from the year before. You need to destroy them. You can use urea fertilizer to burn them chemically, though some growers prefer to actually burn them out with flames.
Otherwise, be very careful about controlling weeds under your bushes, and rake away the detritus at the end of the season, being particularly certain to remove the fruit mummies. Your best bet is to burn any infected or potentially infected material. If that's not possible, bury it far away from your blueberry bushes.
One more point: don't eat any infected fruit, and especially don't try to eat the fruit mummies. They probably won't hurt you, but they'll taste horrible; and if you're growing to sell, never, ever allow any into your produce.
Don't worry, though, if birds or animals eat them; as it turns out, that's a good way to help control a mummyberry infection.