Hello everyone,
As we move into May, we will begin publishing regular
blog updates to provide producers with timely information on field development
and seasonal management outlooks. Particular attention will be given to blight
disease management, including Monilinia Blight (Mummy Berry) and Botrytis
Blossom Blight (Grey Mould).
Season Progress and Crop Development
This season’s first blight update is being released on
May 4, approximately one week later than last year’s first post (April
27, 2025). As many growers experienced, April brought alternating periods of
mild temperatures followed by cooler, late-winter-like conditions. These
fluctuating weather patterns slowed spring crop development compared with last
season.
Despite the slow start, warmer conditions are expected
to accelerate wild blueberry growth in the coming weeks, bringing many fields
into the critical blight-management period.
Mummy Berry Risk and Monitoring
Late-April weather conditions were
favourable for the germination of mummy berries and the development of small
cup-like structures known as apothecia. These structures produce primary
spores that infect susceptible blueberry fruit bud stages (Figure 1).
Producers are encouraged to closely
monitor:
- Fruit bud stage progression in crop fields
- Local temperature and moisture conditions
- Field history and disease risk levels
Careful monitoring will help
determine optimal timing for effective fungicide applications targeting blight
diseases.
Figure
1. Susceptible Fruit Bud Periods
Additional Field Management Reminders
This post also includes early-season updates on
growing degree day (GDD) accumulation and crop F2-stage development in
production fields.
In sprout fields, the window for pre-emergence
herbicide application is approaching. Growers may wish to begin planning
spray operations and take advantage of suitable field and weather conditions
expected over the next several weeks.
In This Update
- Wild
Blueberry Weather Station GDD and Crop F2 Stage Updates
- General
Information on Monilinia Blight and Management Considerations
Have a great week, everyone!
Hugh Lyu
May 4, 2026
Wild Blueberry Weather Station GDDs and Crop F2 Stage Updates
During the 2026 growing season, we will provide
periodic Growing Degree Day (GDD) updates using selected wild blueberry
weather stations located across the province (Figure 2). These updates are
intended to support producers in tracking seasonal crop development and
improving the timing of key management decisions.
Figure
2. Selected Wild Blueberry Weather Stations for GDD Updates in 2026
A summary of selected wild blueberry weather stations and their accumulated
GDD totals from April 1 to May 3
is presented below (Figure 3).
Figure
3. Accumulated Growing Degree Days (April 1–May 3, 2026)
When compared with the local wild blueberry GDD model for F2 stage development (Figure 4), it is
important to note that we are currently in the early stages of F2 development,
during which fungicide applications are generally not required.
Based on the current 14-day weather forecast,
several potential infection periods are expected across most Mainland wild
blueberry production areas. During this time, many crop fields are expected to
reach a stage in which more than 40% of fruit buds have separated their bud
scales, indicating increased susceptibility to Monilinia blight.
To support management decisions, we have
included additional information below outlining key wild blueberry crop stages
and practical guidance on Monilinia Blight biology and management for those
interested in reviewing the fundamentals of this disease and its effective
control strategies.
Figure
4. Wild Blueberry F2% and GDDs
We will continue
providing updates on F2 stage percentages across different production
regions as information becomes available throughout the season.
Table 1. Percentage of Wild Blueberry Floral
Bud F2 stage
light green (0-20% F2), dark green (20-30% F2), yellow
(30-40% F2) and red (40-100% F2)
|
Wild blueberry production regions, NS |
The average percentage of floral buds at
F2 |
|
|
|
|
Cape Breton |
|
|
|
|
|
Cumberland County |
|
|
|
|
|
South West Nova Scotia |
|
|
|
|
|
Hants County |
|
|
|
|
|
Halifax County |
|
|
|
|
|
Guysborough County |
|
|
|
|
|
Colchester County |
|
|
Murray Siding/ Truro |
25% F2 |
|
|
|
|
|
|
|
Pictou and Antigonish County |
|
|
|
|
General Information about Monilinia Blight and Management
The following recommendations are
intended to support producers in managing Monilinia Blight (Mummy Berry)
during the early infection period of the wild blueberry crop.
Key
Management Considerations
1. Field History and Risk Awareness
Fields with a known history of Monilinia blight require close monitoring each
season. Where infections have persisted for multiple years, producers should carefully track F2-stage development alongside local weather conditions
to prepare for timely fungicide applications.
2. Determining F2 Percentage in Your
Field
Knowing the F2 percentage is essential for proper spray timing (Figure 5).
To estimate F2 development:
- Walk the field in a random “W” pattern.
- Collect 20–30 stems representing different areas
of the field.
- For each stem:
- Count the total number of floral buds.
- Count the number of buds at the F2 stage or beyond.
Calculate F2% for each stem using
the following formula:
F2% = (Number of F2 or more advanced
buds ÷ Total floral buds) × 100
The overall field F2% is obtained by
averaging the F2 percentages from all sampled stems.
3. Infection Risk Threshold
Once crop fields reach approximately 40% F2, wild blueberry
tissues—including fruit buds and emerging leaf tissue—become susceptible to
infection when environmental conditions favour mummy berry cup development,
spore release, and infection events.
4. Fungicide Timing
When fields exceed 40% F2, fungicide protection is recommended:
- Before forecast wet periods, or
- Shortly after an identified infection period.
5. Protection Window
Most registered fungicides provide approximately 7–10 days of protection.
A second application may be required if favourable infection conditions
persist.
6. Fungicide Selection
Before finalizing a fungicide program, producers should consult their
processor’s approved chemical list for the season.
Perennia’s Online Pest Management
Guides can assist with product selection and application planning:
- Online Pest Management Guide: https://www.perennia.ca/onlinepestmanagementguide/
7. Resistance Management
To reduce the risk of fungicide resistance development, rotate fungicide groups
and modes of action whenever possible.
8. Factsheet Resources
- NS Monilinia Blight Factsheet: https://cdn.dal.ca/content/dam/dalhousie/images/sites/wild-blueberry/pdfs/Monilinia_Blight_Lowbush_Blueberry.pdf.
- NB Monilinia Blight Factsheet: https://www2.gnb.ca/content/dam/gnb/Departments/10/pdf/Agriculture/WildBlueberries-BleuetsSauvages/C310-E.pdf.
Figure
5. Wild Blueberry Floral Buds in F1 and F2 stages.