Blueberry Mummy Berry Disease — What It Is and How to Stop It

Mummy berry is one of the most distinctive blueberry diseases: instead of ripening blue and sweet, affected berries turn a pale tan or salmon colour, harden like small stones, shrivel and hang on the bush long after healthy fruit has been harvested. Cut one open and the inside is dry, brown and completely inedible. The disease is caused by the fungus Monilinia vaccinii-corymbosi, and it has a two-stage life cycle that makes understanding it essential to controlling it.

Understanding the two-stage life cycle

The fungus overwinters as sclerotia — small hard structures — in the mummified berries that fall to the ground beneath the bush. In spring, these sclerotia germinate into small cup-shaped fruiting bodies called apothecia that release spores into the air at exactly the time the blueberry is producing new shoot growth. The spores infect the new shoots and leaves, causing them to wilt, brown and look as if they have been hit by a late frost — this is the first stage of the disease. These infected shoots then produce a secondary crop of spores that are carried by pollinators to flowers, where they infect the developing fruit. The infected berries develop normally through the season until they should ripen — and then mummify instead.

The most effective control: remove the mummies

The entire disease cycle depends on those overwintering mummies on the ground. Raking them up and removing them in autumn, before spring, breaks the cycle at its most vulnerable point. This single cultural practice is the most effective control measure available. Do not compost the mummies — destroy them or dispose of them in household waste. Thick mulching applied before bud break can also suppress apothecial germination by burying the mummies, though mulching is no substitute for removal.

Spring monitoring and early intervention

Watch for the first stage — wilted, browned shoot tips appearing at bud break that look like frost damage but affect random shoots rather than the most exposed ones. Remove and destroy all affected shoot growth promptly. Copper-based fungicide applied at bud break and repeated through bloom is effective where the disease has been severe in previous years, but the timing must match the spore release period closely to be effective.

After harvest

After harvest, collect every mummified berry from the bush and the ground. Do not leave any on the soil surface over winter. If the disease has been severe, consider applying a layer of fresh bark mulch over the existing soil surface to cover any sclerotia you may have missed.