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Ministry of Agriculture, Food and Rural Affairs

Angular Leaf Spot

Symptom of angular leaf spot infection - white flaky dried up ooze Symptom of angular leaf spot - water-soaked lesions on lower leaf surface Symptom of angular leaf spot - infected calyx Symptom of angular leaf spot - yellowing on upper leaf surface Bacterial ooze on lower leaf surface Symptoms of angular leaf spot on lower leaf surface
Click to enlarge.

Beginner

Scientific Name
Xanthomonas fragariae

Identification

  • Symptoms develop on the leaves and the fruit calyx.
  • Tiny angular spots are first evident on the lower leaf surface.
  • Spots look wet when viewed from above, translucent when held up to the light.
  • Spots enlarge into angular shaped, dark green limited by small veins.
  • Lesions expand and join together to become irregular reddish-brown spots with necrotic areas on the upper leaf surface.
  • Bacteria ooze out of these spots in humid weather, dry up and leave flaky residue.
  • Infected sepals turn black.

Often Confused With
Leaf Spot
Leaf Scorch
Leaf Blight
Spray burn (calyces)  

Period of Activity
Disease pressure is highest where overhead irrigation has been used to protect against frost.  Symptoms are expressed in warm humid weather.

Scouting Notes
Scout pre-bloom, bloom and new plantings after prolonged periods of rain and high relative humidity.  Look for initial symptoms on lower leaves.  Make notes on the progress of the disease from older lower leaves to new growth and calyces
           
Thresholds

 None established.

Advanced

Scientific Name: Xanthomonas fragariae

Identification
Symptoms of angular leaf spot develop on the leaves and the fruit calyx. Tiny angular spots are first evident on the lower leaf surface.  Spots enlarge into angular shaped dark green, limited by small veins.  The spots look wet when viewed from above but are translucent when held up to the light.  Bacteria ooze out of these spots in humid weather.  When the ooze dries up, it leaves white flaky residue.  Lesions expand and join together to become irregular reddish-brown spots with necrotic areas, visible on the upper leaf surface.  Infected sepals turn black and make the fruit unmarketable.  This disease can be systemic on the plant; sometimes it causes plants to collapse.

Often Confused With
Leaf spot
Leaf scorch
Leaf blight (Angular leaf spot causes characteristic wet, angular-shaped spots on the lower leaf surface that are transparent when back-lit.  As the disease progresses, yellowing occurs on the upper leaf surface which can be confused with leaf blight.)
Spray burn (Dark or dry calyces can be caused by other leaf diseases or by spray burn.  Calyces infected with angular leaf spot have a darker brown to black, almost wet, colouration.)

Biology
Angular leaf spot is also known as bacterial blight.  The disease attacks cultivated and wild strawberries, but has no alternate hosts.  It is caused by the bacterium Xanthomonas fragariae.  The bacteria overwinter on infected plant debris in the soil, or on strawberry plants.  In the spring, bacteria become active and are spread around the plant and to new uninfected plants by splashing rain or irrigation.  The first infections are visible on older leaves near the base of the new plant.  New infections develop when the bacteria is splashed to new growth or the sepals.  The bacteria enter plants through wounds or natural plant openings.  The infection may become systemic and infect all plant parts except the roots.  Fruit can become infected which results in black calyces and hard, unattractive areas on the shoulder.

Period of Activity
The disease is present on plants all season long.  Conditions which favour its development are cool, wet days when highs are around 20°C (68°F) and lows around freezing (0°C or 32°F).  Disease pressure is highest where frost has been frequent during bloom and overhead irrigation has been used to protect against it.  Cool spring conditions with frequent rainy periods are ideal for the development and spread of this disease.  Symptoms are expressed in warm humid weather.  When warm, dry conditions prevail, activity and spread of the disease slows down until late summer and fall.

Scouting Notes
Scout established plantings at pre-bloom, bloom, late summer or fall.  Scout new plantings in spring, late summer and fall.  Scout after prolonged periods of rain and high relative humidity (RH > 90%).  Check the underside of older leaves in spring for signs of angular leaf spot.  Estimate the percent of plants infected and the severity of the infection.  Make notes on the progress of the disease from the older leaves at the base of the plant to the newer growth and calyces.

Symptoms develop within 5- 6 days at 20- 25°C (68- 77°F); 14 days at 10°C (50°F).  No symptoms are observed on infected plants at 5°C (41°F) but disease will develop when temperatures increase.

All varieties are susceptible to angular leaf spot; Cavendish, Annapolis, Kent, Allstar, Sable, Wendy, Honeoye and Jewel are extremely susceptible.

Thresholds
None established.

Management Notes

  • Angular leaf spot is a bacterial disease and is not controlled by fungicides.
  • Avoid excessive irrigation for frost protection.
  • Avoid excessive nitrogen because younger leaf tissue and leaves on very vigorous plants are most susceptible.
  • Clean up crop debris, especially on plastic-mulched beds.
  • Avoid work in fields when they are wet.
  • Bacteria can travel within the plant from leaves to crowns and can be spread to new fields on symptom-less propagation material. Purchase plants from a professional plant grower who uses an accredited plant propagation program.  
  • Within the field, the disease is spread by irrigation water, splashing rain, wet equipment, etc.