Northwest berry Foundation

Management Detail

Alternaria Fruit Rot

in Blueberries

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Latin name: Alternaria spp.


Reason for Concern:
1) Although not as common as ripe rot, this disease has caused severe losses in some fields.
2) Infections can occur any time between late bloom through fruit maturity.
3) Infections remain latent until fruit ripens.
4) The disease often is not seen in the field but develops in storage or in transit to market.

Leaf lesions are circular to irregularly shaped, tan to gray, 1 to 5 mm in diameter, and surrounded by a reddish brown border. In most cases only lower leaves are infected, but a severe infection can defoliate the plant. On ripe fruit, sunken areas near the blossom end of the berry are covered by a dark green, velvety growth. On stored fruit, a grayish-green mold may appear on the stem scar or berry end and spread over the entire berry. Infected fruit becomes soft and shriveled. Although berries may be dry in the field, the rot can become watery when harvested fruit is stored. Infected berries also tend to break open easily.

The Alternaria fungus overwinters on the ground, on and in twigs, and on debris. Leaf infections occur in the spring during periods of cool, wet weather. Infected tissue produces spores that are transferred to fruit by wind and other means. Fruit infection may occur as berries start to ripen, before harvest, or during the post-harvest period. Disease development is optimal at 68ºF.



  • Start monitoring fruit early in the ripening season.
  • Look for greenish gray mycelium and dark olive-green spores that mark an Alternaria infection.
  • Fungal growth either starts at the blossom end or stem scar end of the berry and can completely engulf the berry.

Cultural Controls:

  • Avoid wounding or bruising fruit during harvest.
  • Harvest frequently to avoid overripe fruit.
  • Cool berries rapidly after harvest.
  • Avoid overhead irrigation if possible.


For information about chemical controls, check with our Pesticide Guide.


photo from Michigan State University

photo from Michigan State University

photo from Michigan State University


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