Stamen blight

This disease affects flowers and buds on plants, anthers are swollen, brown, and do not shed pollen

Caused by a fungus Hapalosphaeria deformans. This disease affects Boysenberry, Marion, Evergreen Thornless, and other cultivars with wild trailing blackberry in parents. The disease is severe in some plantings, severity varies markedly from year to year. Rain splashes spores from infected flowers to axillary buds of primocanes during bloom. The infection process occurs in summer.
Stamens of infected flowers are flattened against the petals instead of in an upright ring. Anthers are swollen, brown, and do not shed pollen. Since sporulation occurs before the flower opens, 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 cultivars 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.
Use plant spacing and canopy management that promotes good air movement.
Direct sprays onto primocanes in the every-year fruiting system any time between flowering and harvest.
Captan 80 WDG at 2.5 lb/A. Do not apply within 3 days of harvest. Although this disease is not on the label, Captan has been shown to be effective. Group M4 fungicide. 48-hr reentry.