Michigan Blueberry Facts: Fruit Rot Identification Guide
May 1, 2003 - Author: Phillip Wharton and Annemiek Schilder
Anthracnose rot (Colletotrichum acutatum)
A major postharvest rot of blueberries in Michigan, characterized by wet, orange spore masses. Symptoms may develop rapidly (2 to 4 days) when fruit is stored at room temperature.
Alternaria rot (Alternaria spp.)
A common postharvest rot of blueberries in Michigan, characterized by greenish gray mycelium and dark olive-green spores. Fungal growth often starts at the stem scar and can completely engulf the berry.
Gray Mold (Botrytis cinerea)
A less common postharvest rot of blueberries in Michigan, characterized by fast-growing, tan to gray, fluffy mycelium and tan spore masses on brown stalks. It can be distinguished from Alternaria rot, because the mycelial growth is less dense and more gray than green.
Phomopsis rot (Phomopsis vaccinii)
Occurs mainly in fruit harvested from fields with Phomopsis twig blight and is characterized by cream-colored spore droplets oozing out of pimple-like fruiting bodies. When dry, the droplets may appear light yellow.
Mummy berry (Monilinia vaccinii-corymbosi)
Though not considered a fruit rot, this is a major disease of blueberries in Michigan, characterized by shriveled, white to purplish gray berries. Inside, the fungus has replaced fruit tissue to form a hard, black sclerotium.
Pestalotia rot (Pestalotia vaccinii)
A sporadic postharvest rot characterized by black, inky spore masses that may be accompanied by creamy white mycelium.
Hainesia rot (Hainesia lythri)
A sporadic postharvest rot characterized by dark pink to maroon, button-shaped spore masses. As spore masses dry out, they turn dark brown to black and develop an indentation in the center.
Yeast rot (Aureobasidium pullulans)
A sporadic postharvest rot characterized by a rapid collapse and wet or slimy appearance of the berry. Yeast growth may be apparent as black, shiny bumps and white or pinkish slime.
Aspergillus rot (Aspergillus spp.)
A rare postharvest rot characterized by chocolate-brown, powdery spore masses at the ends of thin, white stalks.
Epicoccum rot (Epicoccum nigrum)
Uncommon in Michigan; characterized by growth of a dense, orange-yellow mycelium, usually at the stem scar.
Rhizopus rot (Rhizopus stolonifer)
A rare fruit rot that causes berries to collapse quickly. Round, dark gray spore masses are borne on hair-like stalks.
White Mold (Trichoderma spp.)
A rare postharvest rot characterized by white mycelium resembling cotton balls growing on the blueberry surface.
Alternaria and Colletotrichum
Phomopsis and Colletotrichum
Pestalotia and Colletotrichum
Pestalotia and Alternaria