Cause Diaporthe vaccinii (asexual Phomopsis vaccinii), a fungus that overwinters in infected plant debris. In the spring, spores are dispersed from fruiting bodies (pycnidia) embedded in diseased tissue by rain splash and irrigation water. Infection occurs through flower buds from budbreak to bloom. The disease spreads from flowers into shoots and twigs. The fungus can also infect through injuries such as wounds from pruning, harvest equipment, frost cracks and herbicide injury and produces girdling cankers. The fungus can also cause a fruit rot. Historically the disease was not common in the Pacific Northwest but has grown in importance in British Columbia with the planting of 'Draper' and 'Liberty'. The disease can get established in newly planted fields where fungicides are not regularly used. 'Duke', 'Legacy' and 'Powderblue' were, on the average, more susceptible while 'Rubel' was more resistant under controlled conditions.
Symptoms Dieback of flowers, twigs, and shoots. Cankers may be present at the base of infected canes. Cankers are seen as elongated, flattened areas that become covered with small, pinpoint-sized fruiting bodies (pycnidia) that produce spores. Tissue around the canker can appear silvery and speckled with black dots. Infected stems will wilt during the summer and the leaves turn color earlier, causing a red flagging. Can be confused with bacterial canker.
- Purchase healthy planting material and/or do not use plants with injured branches.
- Prune out, remove, and destroy infected and dead branches. Prune 5 to 6 inches below symptoms.
- Avoid wounding or injuring plants.
- Encourage plants to harden off in winter to avoid frost damage.
- Provide adequate plant spacing and manage canopy size to promote good air circulation.
Chemical control The fungus may be active anytime it rains in the spring from bud break to harvest but focus applications during bloom.
- 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 plus spreader-sticker. May be applied up to day of harvest. Group M4 fungicide. 48-hr reentry.
- Fontelis at 16 to 24 fl oz/A. Can be used day of harvest. Group 7 fungicide. 12-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.
- Miravis Prime at 9 to 13.4 fl oz/A. May be used day of harvest. Group 7 + 12 fungicide. 12-hr reentry.
- Omega 500 F at 1.25 pint/A. Do not use with an adjuvant or within 30 days of harvest. 12-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.
- Quash at 2.5 oz/A. Do not use within 7 days of harvest. Group 3 fungicide. 12-hr reentry.
- QuiltXcel at 14 to 21 fl oz/A. Do not use within 30 days of harvest. Sprayers should not be used on apples. Group 3 + 11 fungicides. 12-hr reentry.
- 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.
- Tilt at 6 fl oz/A. Do not use within 30 days of harvest. Group 3 fungicides. 12-hr reentry.
- 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. Unknown effectiveness in the PNW. 4-hr reentry. O
References Parker, P.E. and Ramsdell, D.C. 1977. Epidemiology and chemical control of phomopsis canker of highbush blueberry. Phytopathology 67:1481-1484.
Polashock, J. J., and Kramer, M. 2006. Resistance of blueberry cultivars to botryosphaeria stem blight and phomopsis twig blight. HortScience 41:1457-1461.