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Beginner

Scientific Name
Diplocarpon earlianum

Identification

• Infects leaves, runners, flowers, fruit and calyx.
• Infected leaves initially appear to have numerous purplish-brown blotches.
• Lesions join together and may turn bright red.
• Leaves eventually turn brown, dry up and curl up at the edges giving a burned or “scorched” appearance.

Often Confused With
Powdery mildew

Period of Activity
Leaf scorch can infect strawberry leaves at all stages of development.  Most infections take place in early spring, or mid-August to late September- when most leaves are young and frequent rains or heavy dews provide good conditions for infection.  The optimal temperature for germination occurs between 20 and 25°C (68- 77°F) but germination can occur at temperatures between 5°C and 30°C (41- 86°F) with a sufficient wetting period (at least 6- 9 hours).  Symptoms appear within 7- 9 days after infection and spores are produced within 10- 14 days.

Scouting Notes
Monitor for leaf scorch in early spring to assess whether early sprays are needed.  Check susceptible cultivars such as Allstar, Kent and Micmac for first 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
Diplocarpon earlianum

Identification
Leaf scorch usually infects leaves and calyces; occasionally it infects runners, flowers and fruit.  Leaves develop numerous purplish-brown blotchy lesions.  These lesions join together and may turn bright red.  Leaves gradually turn brown, dry up, and curl at the edges giving them a burned or scorched appearance.

Often Confused With
Powdery mildew (Powdery mildew produces purple spots that are variable in size, from specks to flecks to larger spots.  There is slight yellowing in purpled areas.  Leaf edges curl and large areas of the lower leaf surface become discoloured- pink or grey.)

Biology
The fungus, Diplocarpon earlianum, overwinters in both living and dead strawberry leaves.  In Ontario, both conidia and ascospores may be initial sources of leaf scorch in the spring and germinate under wet conditions leading to the infection of new strawberry tissue.  Leaf lesions produce conidia throughout the growing season which allows for repeated infections.  Younger leaves tend to be more susceptible to infection than older leaves.  Inoculum and disease pressure are higher in older plantings because there is more leaf litter and the disease has had to time to build up on the older leaves.

Period of Activity
Leaf scorch can infect strawberry leaves at all stages of development.  Most infections take place in early spring, or mid-August to late September- when most leaves are young and frequent rains or heavy dews provide good conditions for infection.  The optimal temperature for germination occurs between 20 and 25°C (68- 77°F) but germination can occur at temperatures between 5°C and 30°C (41- 86°F) with a sufficient wetting period (at least 6- 9 hours).  Symptoms appear within 7- 9 days after infection and spores are produced within 10 - 14 days.

Scouting Notes
Monitor for leaf scorch in early spring to assess whether early sprays are needed.  Check susceptible cultivars such as Kent, Wendy, St. Pierre and Valley Sunset for 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.  Susceptible varieties and/or fields with high levels of disease the previous year should be treated early the following spring. Wet weather combined with the presence of the disease increases the need for fungicides.

Management Notes

• Plants affected by leaf scorch do not overwinter well, and yields the following year may be reduced.
• Conditions which favour the disease are susceptible cultivars, perennial plantings, and repeated leaf wetness periods of 5- 9 hours or longer.
• Use resistant cultivars where practical.
• On susceptible cultivars, fungicides are recommended in early spring, and again in later summer and early fall.
• Choose crop management practices that keep rows narrow and encourage air flow in the row.