Northwest berry Foundation

Management Detail

Stamen Blight

in Blackberries

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Latin name: Hapalosphaeria deformans

Description:

Reason for Concern:
1) When present, this disease can be severe.
2) Affects blackberries and hybrid berries, particularly Boysenberry.
3) Infects at early bloom more severely than during peak bloom.

Identification/Symptoms:
Infected flower stamens flatten against petals instead of standing in an upright ring. Anthers swell, brown, and do not shed pollen. Open flowers appear white and powdery. Leaf like structures form at sepal tips and double the number of petals. Some species of blackberry may show a witches' broom of the inflorescences. Hard fruit develops and is difficult to remove from the receptacle. Many drupelets fail to develop or develop and ripen unevenly.

Disease Cycle:
Affects 'Boysenberry', 'Youngberry', 'Marion', 'Evergreen', wild trailing blackberry and European raspberries. Severe in some plantings, but severity varies markedly from year to year. Rain splashes spores from infected flowers to primocanes buds. Sporulation occurs before the flower opens. The infection process is not well understood but occurs in summer.

Links:

Scouting:

  • Stamens of infected flowers are flattened against the petals instead of in an upright ring.
  • Anthers are swollen, brown, and do not shed pollen.
  • The flower has a white, powdery appearance when open.
  • Flowers may have symptoms on sepals: leaf like structures at the tips and double the number of petals.
  • Some species of blackberry may show a witches' broom of the inflorescences.
  • If fruit develops, the receptacle is constricted, and a number of druplets either fail to develop or do so unevenly.
  • Ripening may be uneven, and fruit is hard and difficult to remove from the receptacle.
  • At early bloom look for symptoms in susceptible varieties.
  • Scout 4 locations in the field with 40 flowers per location. Note presence or absence.

 
Cultural Controls:

  • The alternate-year fruiting system of growing blackberries controls the disease by removing the inoculum source from above the developing primocanes.

 

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

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from Oregon State University

 

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