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Beginner

Scientific Name
Mycosphaerella fragariae

Identification

• Leaf infections first appear as small, deep-purple, round spots, 3- 6 mm (1/8- ¼ in.) in diameter, on the upper leaf surface.
• As the disease progresses, the centres of the spots turn brown, then grey and eventually white on older leaves.
• A definite reddish to rusty brown border surrounds the grey, necrotic centre area of the disease lesion.

Often Confused With
Leaf scorch
Leaf blight

Period of Activity
Infections can occur throughout the growing season.  Lesions can develop at temperatures from 5- 30°C (41- 86°F), the optimum being 15- 25°C (59- 77°F).  At least 12 hours of leaf wetness are needed for leaves to become infected.  Lesions appear anywhere from 8- 18 days after infection.  Sporulation on these lesions starts about 14 days after infection and lasts for 2- 3 days.

Scouting Notes
Scout fields after prolonged rainy periods, high humidity (98- 100% RH), and warm temperatures (20- 25°C or 68- 77°F).  Monitor for leaf scorch in early spring to assess whether early sprays are needed.  Check susceptible cultivars, such as Kent, first for disease symptoms.  Examine middle-aged leaves during the harvest period to assess whether a protectant spray is needed after renovation.  Monitor from mid-August to early October to determine disease pressure for next year.

Thresholds

None established.

Advanced

Scientific Name
Mycosphaerella fragariae

Identification
Leaf infections first appear as small, deep-purple, round spots, 3- 6 mm (1/8- ¼ in.) in diameter, on the upper leaf surface.  As the disease progresses, the centres of the spots turn brown, then grey and eventually white on older leaves.  A definite reddish-to-rusty brown border surrounds the grey, necrotic centre area of the disease lesion.  In wet years, and in the presence of abundant overwintering inoculum on diseased leaves, leaf spot may infect sepals, leading to secondary infection by grey mould.

Often Confused With
Leaf scorch
Leaf blight (Common leaf spot can be distinguished by the grey centers.)

Biology
The main source of inoculum is the overwintering leaf lesions.  Spores are produced on living and dead leaves, and are spread by wind and splashing rain.  The duration and intensity of the rain are the major weather factors influencing disease development.  Spores germinate and enter the leaf through stomata on the lower leaf surface.  Leaves less than 10 days old are most susceptible to infection.  Leaves more than 15 days old are almost completely resistant.  The disease cycle continues as long as conditions are favourable.

Period of Activity
Infections can occur throughout the growing season.  Lesions can develop at temperatures from 5– 30°C (41- 86°F), the optimum being 15– 25°C (59- 77°F).  At least 12 hours of leaf wetness are needed for leaves to become infected.  Lesions appear from 8– 18 days after infection.  Sporulation on these lesions starts about 14 days after infection and lasts for 2– 3 days.

Scouting Notes
Scout field after prolonged rainy periods, high humidity (98- 100% RH), and warm temperatures (20- 25°C or 68- 77°F).  Monitor for leaf scorch in early spring to assess whether early sprays are needed.  Check susceptible cultivars, such as Kent, first for disease symptoms.  Examine middle-aged leaves during the harvest period to assess whether a protectant spray is needed after renovation.  Monitor from mid-August to early October to determine disease pressure for next year.

Thresholds
None established.

Management Notes

• Use resistant cultivars where practical.
• Choose crop management practices that keep rows narrow and encourage air flow in the row.
• On susceptible cultivars, fungicides are recommended in early spring, and again in late summer and early fall.
• Sprays should be applied to protect plants during periods of rapid leaf growth.  Good spray coverage of both upper and lower leaf surfaces is required.
• Susceptible cultivars include: Kent, Micmac, Sparkle, Startyme, and Veestar.