Cause Alternaria tenuissima, a fungus. This disease has caused severe losses in some Oregon fields, although it is not as common as ripe rot. The fungus overwinters as mycelium and spores in old, dried-up berries, dead twigs from the previous season's crop and on other plant debris. Infections can occur any time between late bloom through fruit maturity. Infections remain quiescent (latent) until fruit ripens. The disease often is not seen in the field but develops in storage or in transit to market.
Symptoms As fruit ripens, the first symptom is a shriveling or caving-in of the side of the berry. This deformity is generally located near the flower end of the berry. The damaged part may be covered with a blackish or dark greenish mass of spores that gives the surface of the berry a dull cast. 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.
Sometimes leaf lesions occur and are circular to irregularly shaped, tan to gray, about 0.25 inch or less in diameter, and surrounded by a reddish brown border. In most cases only lower leaves are affected.
- Harvest promptly to prevent overripe fruit.
- Do not pick or handle fruit when it is wet.
- Hand harvesting results in less rot than machine harvesting.
- Avoid wounding or bruising fruit during harvest.
- Cool berries rapidly after harvest.
- Clean plant debris from picking buckets, packing lines and inspection belts frequently.
Chemical control Spray after full bloom when berries are developing. Bloom applications have not been very effective.
- Abound at 6 to 15.5 fl oz/A. Do not apply with silicone-based surfactants. May be applied on the day of harvest. Group 11 fungicide. 4-hr reentry.
- Captan 80 WDG at 1.25 to 3 lb/A. May be applied up to day of harvest. Moderate control ranking. Group M4 fungicide. 48-hr reentry.
- Indar 2F at 6 fl oz/A plus a wetting agent. Do not use within 30 days of harvest. Group 3 fungicide. 12-hr reentry.
- Inspire Super at 16 to 20 fl oz/A. Do not apply within 7 days of harvest. Group 3 + 9 fungicide. 12-hr reentry.
- Luna Tranquility at 13.6 to 27 fl oz/A. May be used day of harvest. Group 7 + 9 fungicide. 12-hr reentry.
- Oso SC at 3.75 to 13 fl oz/A. May be applied on the day of harvest. Group 19 fungicide. 4-hr reentry.
- Ph-D WDG at 6.2 oz/A plus an adjuvant. May be applied on the day of harvest. Group 19 fungicide. 4-hr reentry.
- Pristine at 18.5 to 23 oz/A. Do not use with any other tank additive except Captan. Can be used day of harvest. Group 7 + 11 fungicide. 12-hr reentry.
- Proline 480 SC at 5.7 fl oz/A. Do not use within 7 days of harvest. Group 3 fungicide. 12-hr reentry.
- Quash at 2.5 oz/A. Do not use within 7 days of harvest. 12-hr reentry.
- Quadris Top at 12 to 14 fl oz/A plus a surfactant. Do not apply within 7 days of harvest. Group 3 + 11 fungicide. 12-hr reentry.
- Sil-Matrix at 1 to 4 quarts/100 gal water plus a nonionic surfactant. Can be applied up to the day of harvest. 4-hr reentry. O
- Switch 62.5 WG at 11 to 14 oz/A. May be used up to and including the day of harvest. Group 9 + 12 fungicide. 12-hr reentry.
- Vacciplant at 14 to 22 fl oz/A. Can be used day of harvest. Unknown efficacy in the PNW. Group P4 fungicide. 4-hr reentry.
- Ziram 76 DF at 3 lb/A. Do not apply after 3 weeks from full bloom. Moderate control ranking. Group M3 fungicide. 48-hr reentry.
Note Although Bravo products are registered on blueberry, they have not been shown effective against this disease and cannot be applied after early bloom.
Some registered products offer only suppression of this disease and thus are not recommended for use. These products include Aliette.
- Serenade ASO (Bacillus subtilis strain QST 713) at 2 to 4 quarts/A. Active ingredient is a small protein and may be used on day of harvest. Serenade Garden Disease Control is available for home use. 4-hr reentry. H O
References Bristow, P.R. and Windon, G.E. 1998. Epidemiology of Alternaria fruit rot in the Pacific Northwest. pp. 176-179. In W.O. Cline,. and J.R. Ballington (eds.). Proc. 8th North American Blueberry Research and Extension Workers Conf. May 27-29, 1998. Wilmington, NC. 293 pp.
Mehra, L.K., MacLean, D.D., Savelle, A.T., and Scherm, H. 2013. Postharvest disease development on southern highbush blueberry fruit in relation to berry flesh type and harvest method. Plant Disease 97:213-221.