Fruit IPM Fact Sheet

Mark Longstroth

Mummyberry is probably the most commonly known disease of blueberry. It is caused by the fungus Monilinia vacinii-corymbosi. This disease infects both young growing shoots and the fruit. The death of new shoots reduces the yield potential for many years to come. But most growers in Michigan are more concerned about the loss of fruit from fruit infections.

Symptoms

Shoot blight is the first symptom seen after dormancy has broken  Blighted shoots are the result of ascospore infection of emerging leaf buds. A blighted vegetative shoot is visible to the right. A Christmas tree pattern of dead tissue forms from the base of the leave following the leaf veins.

Eventually the whole growing point and current season's growth will die. Death of the growing points and loss of next year's fruit that would have formed on the shoot is a major concern.

Many shoot strikes can be seen on the bush at right.  Most growers do not factor this loss in unless there are many shoot strikes in a field as in this bush. About 50 percent of the shoots were blighted in portions of this field.

Conidiospores form on the blighted shoots. These conidiospores infect the blossoms as they open. The new flowers are most susceptible to infection.  As the flower ages, it becomes more resistant and likely to be infected after 4 days.  The spores are carried by pollinating insects or by the wind to the open flowers.

To the left is a picture of a bee visiting a shoot strike.  The blighted shoots are attractive to bees.  The conidiospores are in a sweet matrix so bees and other insects visit the shootstrike and carry the mummy berry spores to open flowers. This picture clearly shows the bee is working the area of the infection that is covered with spores. 

It is important that growers maintain fungicide protection of the open flowers during bloom when there are shoot strikes in the field.

Evidence of blossom infection does not appear until the fruit begins to ripen. The infection lays dormant until the berry begins to ripen. As normal berries ripen, the infected berries begin to shrivel and turn a pinkish color  These  "mummyberries," are filled with pathogenic fungus. They fall to the ground, shrivel, turn dark brown or black becoming pumpkin-shaped. They serve as an inoculum source the following spring when apothecia form and disease cycle begins again. Crop losses of 30 to 40% are experienced where no fungicidal control is practiced. This loss of the current seasons crop in the main loss suffered by Michigan Blueberry Growers. There is some varietal resistance, but resistant varieties are not an effective disease control strategy.

Disease Cycle:

The fungus has a complex life cycle. The disease infects blueberries twice each year.  Initially, the disease infects the new shoots with ascospores from the overwintering apothecium. The disease overwinters in psuedoscloratia called mummies, formed from last year's infected fruit. Ascospores of the fungus are dispersed from mushroom-like apothecia  that form on last year's mummyberries which overwinter on and in the soil under the bushes. The mushrooms emerge at the same time as the buds of the blueberry bush begin to open. Spores are dispersed from the mushroom as it matures. There is some argument over whether or not a hard killing freeze will kill the mushrooms and the spores. There is little doubt that freeze damaged tissues are more susceptible to infection.

The infected shoots then infect the flowers. The blighted shoots are attractive to bees.  The conidiospores are in a sweet matrix so bees and other insects visit the shootstrike and carry the mummy berry spores to open flowers.

Control: Chemicals applied to the soil do not effectively destroy apothecia. Begin applying fungicides when green tissue is exposed to control the shoot blight phase of the disease.   Applying fungicides to the bushes prebloom and during bloom can give excellent control of the fruit mummy phase of the disease. Refer to the MSU Michigan Fruit Management Handbook, (Extension Bulletin E-154) for current fungicide recommendations, rates and timing.

Check the disease page at the Michigan Blueberry Facts website. There is also a short article on mummyberry there.  

Check the Blueberry Page at this site and the Michigan Fruit Team Blueberry page for other postings especially the blueberry disease page for more blueberry disease information.  Be sure to go to the bottom of the page to check for recent updates.

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First Posted: April 3, 2003
Last modified: June 10, 2009