Mummy berry is the most serious and widespread disease of highbush, lowbush, and rabbiteye blueberries. It is most serious in the north following moist, spring weather conditions. Crop losses can be severe, depending on environmental conditions and variety susceptibility. Blueberry varieties differ in their susceptibility to this disease.
Symptoms and Disease Cycle
Mummy berry is caused by the fungus Monilinia vaccinii-corymbosi. Spores within berries infected by this pathogen can remain viable in or on the soil for several years. In the spring, tips of the newly infected leaves, buds, stems, and flower clusters suddenly will wilt, turn brown, and eventually become covered with a powdery mass of spores produced by the fungus. Spores from these blighted shoots are carried to open flowers along with the pollen. The fungus colonizes the developing fruit by growing into and colonizing the ovaries. When nearly mature, infected berries become dry, shrivel, and drop early. These shriveled berries, on which the fungus will overwinter, are called "mummies." In the spring, cup-shaped fruiting bodies are produced on the mummies and can be found on the soil surface. These fruiting "cups" release spores that infect new plants. Mummy berry usually is more severe in low-lying areas of the field.
Clean cultivation aids in the control of this disease. Remove and dispose of fallen leaves and old berries either by burying or burning. Cover old berries with at least 2 inches of soil by disking between rows or adding 2 inches of new mulch. Before berries blossom, thoroughly cultivate between rows and under plants after each hard rain. An application of urea fertilizer or a shallow cultivation of the ground between rows and beneath infected bushes before bud break kills the exposed mushroom-like apothecia (mummy cups). The Bluetta, Collins, Coville, and Darrow varieties may have some resistance. Susceptible varieties include Berkeley, Bluecrop, Blueray, Earliblue, Jersey, and Weymouth. If using fungicides, apply at bud break and follow up at 10- to 14-day intervals through bloom. This will control the disease effectively. Once the flowers have been pollinated, no further infection can take place.