2026 Disease Management for Wild Blueberry

Prepared by Seanna Annis, Professor of Mycology and Extension Professor.
Published February 2026.

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2026 Disease Management for Wild Blueberry Chart (PDF for printing)

This revised version replaces all previous charts.

Questions About Disease Management?

Contact Seanna Annis, Professor of Mycology and Extension Professor, at sannis@maine.edu.

Cultural Disease Management

Cultural disease management is the foundation of an effective, long-term plant health strategy in wild blueberry production. Rather than relying solely on fungicides, cultural practices focus on reducing disease pressure by modifying the field environment and interrupting pathogen life cycles. By integrating cultural controls with timely chemical applications when needed, growers can improve disease control, reduce resistance risk, protect pollinators and beneficial organisms, and support the long-term sustainability of Maine’s wild blueberry production systems. Explore cultural management strategies for the diseases commonly encountered in wild blueberry fields below.

Cultural Management Methods by Disease

Fire Pruning, use efficient harvesting techniques. Burn pruning can decrease approximately 50% of mummy berries (pseudosclerotia). If litter is too wet, then sanitation will be incomplete.

Mulching with material to a depth of 2″ to 3” before plant emergence after pruning will help to prevent mummy berries from germinating. Mulching under clones with lots of mummy berries visible at harvest can decrease inoculum for following years.

Reducing the number of infected fruits on the ground by high temperature composting or disposing of winnower refuse away from the field can reduce mummy berries in the field.

The fungus can attack hundreds of different plants. Removing early flowering weeds and red sorrel can decrease early infections in those sources. Scouting of early blooming clones for this disease is important.

Fire pruning to decrease infected plant material.

To remove the fungus from infected areas, do intensive fire pruning to destroy all leaf litter in the infected area and within 10 feet of infection. All leaf litter must be eliminated to remove the fungus that can survive in dead leaves for years.

The spores are not carried by wind or water, but can be transported on leaf contaminated equipment, clothing or shoes. If you have infected areas, avoid walking through them in wet conditions. Cleaning equipment before moving it to a new field will help prevent spread.

Fire pruning to decrease infected plant material.

Avoid walking through infected areas when the fungus is spreading spores. The spores appear as white patches on the underside of infected leaves. The spores are produced from approximately middle of June through August.

Fire pruning to decrease infected plant material. Avoid spreading spores (white patches on underside of lesions on leaves) by not walking through diseased areas in the middle of July through August.

None at this time.

Chemical Disease Management

Important: This guide is not a substitute for reading and following pesticide labels. It is unlawful to use any pesticide inconsistently with its label. The user assumes all responsibility for misuse. Trade names are used for identification only. No endorsement is implied. Check with your processor regarding PHI restrictions or MRL restrictions for export sales.

Group 3

Disease(s) Managed:

  • Mummy berry
  • Leaf spots (powdery mildew, Sphaerulina leaf spot, leaf rust)
  • Botrytis blossom blight

Active Ingredient(s): Metaconazole
Signal Word: Caution
Crop Stage(s): Crop Year

Rate:

  • 2.5 oz
  • Maximum: 3 applications, 7.5 oz (0.234 lb ai) per year
  • No more than 2 sequential applications

PHI: 7 days
REI: 12 hours
Aerial/Drone Application: Can be aerially applied.

Important Notes:

  • For mummy berry, apply when >30% stems have blossoms at crown stage.
  • Follow the mummy berry forecast method to time applications or apply every 7–14 days following the calendar method.
  • Demethylation inhibition.
  • Locally systemic.

Human & Environmental Risk:

  • Moderately toxic to fish.
  • Moderately toxic to people.

Disease(s) Managed:

  • Mummy berry
  • Leaf spots (powdery mildew, Sphaerulina leaf spot, leaf rust)

Active Ingredient(s): Propiconazole
Signal Word: Warning
Crop Stage(s): Crop Year

Rate:

  • 6 oz
  • Maximum: 30 oz (0.84 lb ai all propiconazole products) per year
  • No more than 2 sequential applications

PHI: 30 days
REI: 24 hours
Aerial/Drone Application: Can be aerially applied.

Important Notes:

  • For mummy berry, apply when >30% stems have blossoms at crown stage.
  • Follow the mummy berry forecast method to time applications or apply every 7 to 10 days following the calendar method.
  • For Sphaerulina leaf spot, make first application prior to bloom and again after petal fall.
  • If needed, repeat application just after harvest.
  • Demethylation inhibition.
  • Locally systemic.

Human & Environmental Risk:

  • Moderately toxic to fish.
  • Moderately toxic to people.

Disease(s) Managed:

  • Mummy berry
  • Leaf spots (powdery mildew, Sphaerulina leaf spot, leaf rust)
  • Valdensia leaf spot
  • Botrytis blossom blight

Active Ingredient(s): Prothioconazole
Signal Word: Caution
Crop Stage(s): Prune Year, Crop Year

Rate:

  • 5.7 oz
  • Maximum: 2 applications, 11.4 oz (0.356 lb ai) per year

PHI: 7 days
REI: 12 hours
Aerial/Drone Application: Not permitted.

Important Notes:

  • For mummy berry, apply at green tip when >30% stems have blossoms at crown stage.
  • Follow the mummy berry forecast method to time applications or apply every 7 to 10 days following the calendar method.
  • For leaf spot, apply before disease onset and then every 7 to 10 days.
  • Demethylation inhibition.
  • Locally systemic.

Human & Environmental Risk:

  • Moderately toxic to fish.
  • Moderately toxic to people.

Group 3 and 9

Disease(s) Managed:

  • Mummy berry
  • Leaf spots (powdery mildew, Sphaerulina leaf spot, leaf rust)

Active Ingredient(s): Cyprodinil (9) & Difenoconazole (3)
Signal Word: Caution
Crop Stage(s): Prune Year, Crop Year

Rate:

  • 16 to 20 oz
  • Maximum: 80 oz per year
    • 1.3 lb ai cyprodinil
    • 0.46 lb ai difenoconazole
  • No more than 2 sequential applications.

PHI: 7 days
REI: 12 hours
Aerial/Drone Application: Can be aerially applied.

Important Notes:

  • For mummy berry, apply at green tip/when >30% stems have blossoms at crown stage.
  • Follow the mummy berry forecast method to time applications or apply before disease onset.
  • Apply on a 7 to 14-day schedule.
  • No more than 2 sequential applications before alternating to a fungicide with a different mode of action.
  • Demethylation inhibition.
  • Locally systemic.

Human & Environmental Risk:

  • Extremely toxic to aquatic life.

Group 3 and 7

Disease(s) Managed:

  • Mummy berry
  • Botrytis blossom blight

Active Ingredient(s): Fluxapyroxad (7) & Mefentrifluconazole (3)
Signal Word: Caution
Crop Stage(s): Crop Year

Rate:

  • 7 to 10 oz
  • Maximum: 30 oz per year
    • 0.39 lb ai fluxapyroxad
    • 0.39 lb ai mefentrifluconazole
  • No more than 3 applications per year.

PHI: 0 days
REI: 12 hours
Aerial/Drone Application: Can be aerially applied.

Important Notes:

  • For mummy berry, apply at green tip/when >30% stems have blossoms at crown stage.
  • Follow the mummy berry forecast method to time applications or apply before disease onset.
  • Apply at a minimum interval of 7 days.
  • Demethylation inhibition.
  • Locally systemic.

Human & Environmental Risk:

  • Moderately toxic to people.
  • Extremely toxic to aquatic life.

Group 7

Disease(s) Managed:

  • Leaf spots (powdery mildew, Sphaerulina leaf spot, leaf rust)

Active Ingredient(s): Benzovindiflupyr
Signal Word: Danger
Crop Stage(s): Prune Year, Crop Year

Rate:

  • 10.5 oz
  • Maximum: 2 applications; 21 oz per year (0.136 lb ai all benzovindiflupyr products)

PHI: 1 day
REI: 12 hours
Aerial/Drone Application: Can be aerially applied.

Important Notes:

  • For leaf spot, apply at first sign of disease.
  • Non-ionic surfactant or vegetable-based crop oil concentrate recommended.
  • Second application may be made 10 to 14 days later.
  • Do not mix with oxidizing agents.
  • Locally systemic.

Human & Environmental Risk:

  • Extremely toxic to aquatic life.
  • Moderately toxic to people.
  • Moderately toxic to birds.

Disease(s) Managed:

  • Leaf spots (powdery mildew, Sphaerulina leaf spot, leaf rust)

Active Ingredient(s): Isofetamid
Signal Word: Warning
Crop Stage(s): Prune Year

Rate:

  • 13.5 to 15.5 fl oz
  • Maximum:
    • 3 applications at high rate
    • 4 applications at low rate
    • 54 fl oz per year (1.4 lb ai)
  • No more than 2 sequential applications

PHI: 0 days
REI: 12 hours
Aerial/Drone Application: Can be aerially applied.

Important Notes:

  • Start applications prior to disease development.
  • Continue on a 14-day interval if necessary.
  • Locally systemic.

Human & Environmental Risk:

  • Extremely toxic to aquatic life.

Group 7 and 11

Disease(s) Managed:

  • Leaf spots (powdery mildew, Sphaerulina leaf spot, leaf rust)

Active Ingredient(s): Fluopyram (7) & Trifloxystrobin (11)
Signal Word: Caution
Crop Stage(s): Crop Year

Rate:

  • 6 to 7.6 oz
  • Maximum: 27.1 oz per year
    • 0.445 lb ai all fluopyram products
    • 0.445 lb ai all trifloxystrobin products
  • No more than 2 sequential applications.

PHI: 1 day
REI: 12 hours
Aerial/Drone Application: Can be aerially applied.

Important Notes:

  • For leaf spot, apply at critical timings for disease control every 7 to 14 days.
  • Locally systemic.

Human & Environmental Risk:

  • Extremely toxic to aquatic life.
  • Moderately toxic to people.

Group 7 and 9

Disease(s) Managed:

  • Mummy berry
  • Leaf spots (powdery mildew, Sphaerulina leaf spot, leaf rust)

Active Ingredient(s): Fluopyram (7) & Pyrimethanil (9)
Signal Word: Caution
Crop Stage(s): Crop Year

Rate:

  • 16 to 27 oz
  • Maximum: 54.7 oz per year
    • 0.446 lb ai all fluopyram products
    • 2.1 lb ai all pyrimethanil products
  • No more than 2 sequential applications.

PHI: 1 day
REI: 12 hours
Aerial/Drone Application: Can be aerially applied.

Important Notes:

  • For leaf spot, apply at critical timings for disease control every 7 to 14 days.
  • For mummy berry, apply at green tip/when >30% stems have blossoms at crown stage.
  • Follow the mummy berry forecast method to time applications or apply every 7 to 14 days following the calendar method.
  • Locally systemic.

Human & Environmental Risk:

  • Moderately toxic to people.
  • Moderately toxic to fish.

Group 7 and 11

Disease(s) Managed:

  • Mummy berry
  • Leaf spots (powdery mildew, Sphaerulina leaf spot, leaf rust)
  • Botrytis blossom blight

Active Ingredient(s): Pyraclostrobin (11) & Boscalid (7)
Signal Word: Caution
Crop Stage(s): Crop Year

Rate:

  • 18.5 to 23 oz
  • Maximum:
    • 4 applications per year
    • 92 oz per year for all Group 7 or 11 products
    • 23 oz per application for all Group 7 or 11 products
  • No more than 2 sequential applications.

PHI: 0 days
REI: 12 hours
Aerial/Drone Application: Can be aerially applied.

Important Notes:

  • For mummy berry, apply at green tip/when >30% stems have blossoms at crown stage.
  • Follow the mummy berry forecast method to time applications or apply every 7 to 14 days following the calendar method.
  • Avoid applying during bloom when bees are present.
  • May only be applied with water as the carrier.
  • May only be tank mixed with Captan.

Human & Environmental Risk:

  • Extremely toxic to aquatic life.
  • Moderately toxic to people.

Group 9 and 12

Disease(s) Managed: Mummy berry (MB), Botrytis blossom blight (BBB).
Active Ingredient(s): Cyprodinil (9) & Fludioxonil (12)
Signal Word: Caution
Crop Stage(s): Crop Year

Rate:

  • 11 to 14 oz
  • Maximum: 56 oz per year
    • 1.3 lb ai cyprodinil
    • 0.9 lb ai fludioxonil
  • No more than 2 consecutive applications

PHI: 0 days
REI: 12 hours
Aerial/Drone Application: Can be aerially applied.

Important Notes:

  • For mummy berry, apply at green tip/when >30% stems have blossoms at crown stage.
  • Follow the mummy berry forecast method to time applications or apply every 7 to 10 days following the calendar method.
  • Apply when Botrytis symptoms seen in early clones.
  • Apply at 7 to 10-day intervals when conditions favor disease development.
  • Systemic.

Human & Environmental Risk:

  • Extremely toxic to aquatic life.
  • Moderately toxic to people.

Group 17

Disease(s) Managed: Botrytis blossom blight (BBB)
Active Ingredient(s): Fenhexamid
Signal Word: Caution
Crop Stage(s): Crop Year

Rate:

  • 1.5 lb
  • Maximum: 6 lb (3 lb ai all fenhexamid products) per year

PHI: 0 days
REI: 12 hours
Aerial/Drone Application: Can be aerially applied.

Important Notes:

  • Apply at 10% bloom for Botrytis when symptoms seen in early clones.
  • Apply every 7–10 days when conditions favor disease development.
  • No more than 2 consecutive applications.
  • Locally systemic (LOS).

Human & Environmental Risk:

  • Moderately toxic to aquatic life.
  • Moderately toxic to people.

Group M5

Disease(s) Managed: Leaf spots (LS)
Active Ingredient(s): Chlorothalonil
Signal Word: Danger
Crop Stage(s): Prune Year

Rate:

  • 3 to 4 pt
  • Maximum: 12 pt (9 lb ai all chlorothalonil products) per year

PHI: 42 days
REI: 12 hours
Aerial/Drone Application: Can be aerially applied.

Important Notes:

  • Apply in prune year for Septoria (Sphaerulina) leaf spot or leaf rust at 10 to 14-day intervals.
  • Do not add pesticides, fertilizers, or adjuvants unless tested, as phytotoxicity may result.
  • Do not mix with Dipel, Foil, Triton, or Latron.
  • Do not apply after full bloom or may damage developing fruit.
  • High runoff potential for several days to weeks.
  • Not systemic.

Human & Environmental Risk:

  • Extremely toxic to aquatic life.
  • Moderately toxic to people.

Group BM 02

Disease(s) Managed: Mummy berry (MB), Botrytis blossom blight (BBB).
Active Ingredient(s): Bacillus subtilis
Signal Word: Caution
Crop Stage(s): Crop Year

Rate:

  • 2 to 4 qt
  • Maximum: Not specified

PHI: 0 days
REI: 4 hours
Aerial/Drone Application: Can be aerially applied.

Important Notes:

  • For Monilinia suppression, begin application at bud break and repeat every 7–10 days as needed.
  • For Septoria (Sphaerulina) leaf spot or leaf rust, begin application prior to disease and repeat every 7–10 days up to harvest.
  • Spray solution should be pH 4.5–8.5.
  • Not systemic.

Footnotes

Group Number

To reduce the likelihood of fungicide resistance developing in target fungi, growers should rotate between fungicides with different group numbers, ideally using multiple group numbers. Products with the same group number should not be used in consecutive sprays.