Monilinia blight (Monilinia vaccinia-corymbosi)

Monilinia blight: biology

Monilinia blight, or "mummy berry" affects various parts of the blueberry plant with potential for fruit loss. Without proper monitoring and control, the disease can have devastating impacts on blueberry yields. Infected fruit cannot be harvested.

The Monilinia vaccinia-corymbosi fungus overwinters in mummified berries on the ground. During spring, spores from infected berries infect new growth on the blueberry plant to cause wilting, also referred to as blight. This is more likely to happen in wet, cool conditions during the spring. Sites of infection include leaves and flowers. Once Monilinia infects flowers, fruit developing from these infected flowers will become mummified. This infection is also spread via insects to healthy flowers. Although the fruit may appear normal for some time, they will eventually turn off-pink or grey, and wither. The infected fruit then falls on the ground and produces spores the following spring to continue the disease cycle.

It is often difficult to distinguish between Monilinia infection and frost damage until later in the season. Infected leaves turn brown starting at the base of the leaf where the stem is attached. Eventually the entire leaf becomes dark brown and collapses. Individual blossoms and blossom clusters turn brown and wither but remain attached to the plant. Although difficult to see, the fungus is visible on the blossom stem and leaf midrib as a gray or tan mold.

Infected berries may appear normal well into the season. Monitor berries for changing colours such as pink and grey later in the season. When berries become shriveled and lose their outer skin they will begin to resemble small, black pumpkins.