Management of Blueberry Anthracnose and Fungicide Resistance Survey Participants Needed for 2026

Authors: Erica Pate, Jason Lemay and Katie Goldenhar

Blueberry Anthracnose, primarily caused by Colletotrichum fioriniae, causes fruit rot, and to a lesser extent blossom rot and shoot blight. The fungus overwinters on old fruiting spurs and infected twigs and spreads in the spring and summer by rain and wind to infect blooms and fruit. Fruit infections remain latent, and symptoms often show up after harvest once berries are ripe. Infected fruit may begin to soften and shrivel on the bush near harvest time and sticky, orange or salmon-coloured spore masses (Figure 1) will develop on the fruit, reducing yields, marketability, and shelf-life. While fruit rot is the biggest issue, anthracnose can also cause blossom rot and shoot blight. Shoot blight is more common on rapidly growing shoots and on more susceptible cultivars including Bluecrop.  In a 2023 survey of twig blights in Ontario highbush blueberries, 14% of symptomatic shoots were identified as Colletotrichum fioriniae. Twig infections can serve as inoculum for fruit rot infections.

Figure 1: Blueberry anthracnose (Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org).

Most fruit infections occur during bloom to green fruit, especially when weather is warm and wet; there needs to be a minimum of 8 h of leaf wetness at 25°C for infection. Longer leaf wetness is required for infection at lower temperatures. Infections remain latent until the fruit begins to ripen.

Like disease management on other crops, fungicide resistance is also a concern for anthracnose management on blueberries. Colletotrichum fioriniae isolates collected from blueberries in Michigan have been confirmed resistant to group 11 fungicides (Adaskaveg et al., 2025) as well as multiple other US states (Oliver, 2024). No surveys have investigated the presence of fungicide resistance in blueberry anthracnose in Ontario but for 2026 and 2027, OMAFA is leading a survey for detection of the G143A mutation in Ontario blueberry anthracnose.

If you are a blueberry grower and are interested in participating in this survey, please contact Katie Goldenhar, Pathologist- Horticulture (katie.goldenhar@ontario.ca).

Fungicide Management

•  Begin with a preventative spray program in fields with a history of anthracnose fruit rot, applying fungicides starting at pink bud.
• Apply fungicides every 7-10 days during bloom, especially during warm, wet weather.
• Rotate with products from different fungicide (FRAC) groups.
• Do not apply more than 2 consecutive applications of the same FRAC group.
• Fungicides at the fruit ripening stage are not necessary if good control was achieved earlier.
• See registered fungicides and efficacy on the Ontario Crop Protection Hub or in the table below.

Table 1. Fungicides registered in Canada for blueberry anthracnose fruit rot. Always read and follow the label.

Cultural Management

• Choose cultivars with resistance, including Elliott, Draper, Legacy or Liberty. Susceptible cultivars include Bluecrop, Blueray, Patriot, and Toro.
• Prune bushes during dry weather to remove infected twigs and increase airflow and improve drying and pesticide coverage.
• Remove and destroy pruned twigs and canes.
• Use drip irrigation instead of overhead irrigation. If using overhead irrigation, adjust the timing to minimize wetness- irrigate early in the day when dew is already present.
• Harvest regularly to ensure over ripe fruit are not spreading spores.
• Cool fruit as soon as possible after harvest (2°C).
• Avoid harvesting during rain or wet periods.
• Work in areas with known infection last to prevent spreading the disease.
• Disinfect flats and totes between uses.

References

Adaskaveg, A., Neugebauer, K. A., Oudemans, P. V., Hu, M., Gillett, J., & Miles, T. D. (2025). First Report of 129‐L and 143‐A alleles of cytB Conferring QoI Resistance in Colletotrichum fioriniae From Highbush Blueberry in the United States. New Disease Reports, 52(1). https://doi.org/10.1002/ndr2.70058

Oliver, J. (2024). Blueberry disease management: fungicide resistance findings and tools for managing fruit rot. Online presentation: https://extension.uga.edu/content/dam/extension-county-offices/bacon-county/anr/Blueberry-Disease-Update.pdf