Cause Phyllosticta elongata (sexual Botryosphaeria vaccinii), a fungus. The disease is found most often in beds or portions of beds that have soil or crop management problems. The asexual stage is found in the Pacific Northwest and causes a minor fruit rot known as berry speckle. The fungus overwinters in plant debris in and around planting beds. Cool moist weather encourages disease development. Spores are expelled in a gelatinous mass that is soluble in water. This stage is produced during the growing season and is probably spread by water.
Symptoms Runners and uprights defoliate after leaves redden prematurely. Fruiting structures generally do not form until after the leaf or fruit have fallen from the plant. Black, circular, pinpoint-size, subepidermal fruiting structures usually are on one side of the midrib of the lower leaf surface. Fruit develop small light colored lesions about 1 to 2 mm in diameter on the epidermis. Lesions remain light in color while the fruit ripens and turns red around them. Faint red ring spots may also appear on the fruit.
Cultural control
- Remove and destroy plant debris that accumulates at the bed perimeter during flood harvesting operations.
Chemical control
- Delayed dormant spray (buds swollen but no leaves showing) to control stem and leaf blight stage.
- Bordeaux 8-8-100. Do not apply after mid-May. Moderately toxic to fish. Group M1 fungicide. O
- Sprays during early shoot growth may be helpful.
Reference Jeffers, S. 1991. Seasonal incidence of fungi in symptomless cranberry leaves and fruit treated with fungicides during bloom. Phytopathology 81:636-644.
Wells, L.D. and McManus, P.S. 2013. A photographic diagnostic guide for identification of the principal cranberry fruit rot pathogens. Online. Plant health progress. https://doi.org/10.1094/PHP-2013-0729-01-DG