Mummy berry disease of blueberry is often only a minor problem, but it can cause significant fruit losses when the environmental conditions are right. This year may be one of those years.
Now is the time to scout for primary shoot lesions – Alan Eaton recently showed a very nice picture of these in his most recent (May 11, 2017) IPM newsletter. The blueberries at our research farm at the NH Agricultural Experiment Station have quite a lot of primary infections, and we have seen them on some commercial plantings as well.
Most people first notice this disease as fruits start to ripen. Infected fruits develop normally, but just as they should be ripening, they turn pinkish and shrivel to form a hard “mummy” instead of ripening. The fungus that causes mummyberry overwinters in mummified fruit on the ground. In the spring, spores are produced by mushroom-like apothecia on mummified fruit, and are spread by wind. Under cool and wet conditions (like those we have had recently), spores infect green shoots and cause twig blight (primary infection). More spores are produced by infected twigs and leaves. These can then infect blossoms and the fruit they produce (secondary infection).
If fungicides are required, very early applications should begin at bud break, or at the early green tip stage of growth, to prevent primary infections. We are now in bloom in most locations, and that is when we are at risk for secondary infection. Applications of fungicides during bloom can help reduce secondary infections, but after bloom, we have missed the window for control for this year.
Indar 75 WSP (fenbuconazole) currently appears to be the most effective fungicide for controlling the disease, though several other fungicides are labelled (see the New England Small Fruit Management Guide, with blueberry pest management table) and may provide some control.
If infections do occur this year, it will be very important to manage the disease next year. Raking under the bushes very early in the season to disturb the apothecia before they release spores can be effective. Another control strategy is spring mulching to bury the mummies and apothecia, or application of lime sulfur or urea on the soil/mulch surface to ‘burn’ the apothecia.