Latin name: Monilinia vaccinii-corymbosi
Reason for Concern:
1) One of the most serious diseases of blueberry and perhaps the most common.
2) Once established, it can destroy most of the crop.
3) Losses result from killing or blighting of blossoms, blossom and leaf clusters and young shoots, and rotted berries.
4) Yield losses can be nearly 100 % if the disease level is high and the spring is wet.
5) It will also affect the following year’s crop.
6) The potential for loss is greater for primary infection because a single infection can blight all the flowers of 1 cluster.
7) The losses from secondary infection can also be significant but the potential is less because only 1 berry is lost from each infection.
8) All varieties are susceptible to Mummyberry but they differ in susceptibility to the primary and secondary disease stages.
In spring, blighting of new shoot tips and blossoms can be mistaken for frost damage. Developing leaves and shoots suddenly droop. By blossom time, the infected leaf and shoot growth will turn black in the center, then wilt and die. About a week or so after infection, dead areas develop on the petioles and along the midrib and veins of the leaves or, less frequently, at the base of flowers. The dead areas develop brownish gray masses of spores. Infected flowers turn brown and wither. Berries that develop from infected flowers look like healthy fruit during early berry development; cut open, spongy white fungal growth is revealed. As they mature, infected berries turn pinkish and may attain nearly full size before turning tan or gray and shriveling into hard mummies, which drop to the ground at or before harvest. After the fruit skin has weathered off, the berries look like tiny black pumpkins (mummified fruit), that eventually drop to the ground. . In spring, light brown to brown cup-shaped fruiting bodies emerge from the mummies. The tip of the stem is darker and eventually expands into a cup-shaped structure 0.1 to 0.4 inch wide.
The fungus overwinters in the shriveled mummified fruit on the ground. In early spring, cup-shaped mushrooms are produced. These mushrooms mature over a period of several weeks. Spores produced inside the mushrooms are released into the air and carried by the wind to young developing leaf shoots and flowers where they cause primary infections. The optimum temperature for formation of mushrooms and infection is 50 to 57ºF (10 to 14ºC). At least 12 hours of wetness is required for infection. If moisture is not present, the fungus will not produce spores. However, the fungus may survive in mummies for 1 year or more. The fungus produces secondary spores on the dead tissue from the primary infection. These are spread during bloom by wind and insects, and result in secondary infection of flowers. The fungus then colonizes the ovary of the developing fruit. Fruit that develops from infected flowers turns into mummies and falls to the ground. The mummies require a chilling period during the winter before they can start to produce the cups in the spring.
- Mummyberry presence is heavily determined by the history of the field. Fields which have no history of Mummyberry are unlikely (however it is still possible) to suddenly start showing symptoms.
- Scouting should be done by choosing a minimum of 4 random locations per 10-acres and examining 10 plants in each location (increase the number of locations if there is a history of Mummyberry).
- In mid-February, monitor for bud development to determine when bud could become infected. Preventative applications of fungicides should be timed to the green bud stage since leaf and flower buds are infected just as they begin to open.
- From late February through March, examine the base of plants for characteristic fruiting bodies emerging from the previous year’s mummified fruit. Fungal bodies have a distinct inverted cup, they are between 1-3.5cm (1/4”-1”) in size, and their mycelia are always rooted to the hard, year-old, pumpkin shaped, grey fruit.
- As fruit ripens, infected fruit will begin to turn tan colored. This coloration will generally happen right before fruit coloring, so infected fruit are easiest to find while all other fruit is still green. The interior of infected fruit will always have white mycelia formations, making it relatively easy to determine if a suspect infected fruit is in fact an infected fruit.
- Through the harvest season, infected fruit will shrivel and become small, hard, white berries that will eventually drop to the ground.
- Destroy developing apothecia (spore cups) by disrupting the soil under the plants and in alleyways by raking, mulching, or cultivating. Some growers apply the powdered formulation of urea fertilizer to burn the apothecia, while others flame the ground underneath the blueberry plants for the same purpose.
- Sanitation measures include destruction of cull piles near fields, controlling weeds, and letting birds feed on the mummified fruit after harvest.