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Ministry of Agriculture, Food and Rural Affairs

Leaf Blight

Symptoms of leaf blight showing v-shaped lesion and red and yellow colours Symptoms of leaf blight on cultivar MalwinaLeaf blight symptoms Leaf blight early lesions on leaf
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Beginner

Scientific Name
Phomopsis obscurans

Identification

  • Begins as 1 to 6 nearly circular, reddish-purple spots on a leaflet.
  • Spots expand and develop zones:
    • a purple, red or yellow outer margin,
    • a light-brown inner zone,
    • a dark-brown central zone.
  • Infected areas near a major vein are often oval or V-shaped.

Often Confused With
Leaf spot
Leaf scorch
Angular leaf spot

Period of Activity
Symptoms are found most commonly on plants after harvest.

Scouting Notes
Scout for the disease a few days after a rain period that is followed by warm, humid weather during pre-bloom and post harvest.

Thresholds

None established.

Advanced

Scientific Name
Phomopsis obscurans

Identification
This disease begins as 1 to 6 nearly circular, reddish-purple spots on a leaflet.  These spots expand and develop zones:

  • a purple, red or yellow outer margin, which gradually shades off into the normal green leaf colour,
  • a light-brown inner zone,
  • a dark-brown central zone dotted with black pycnidia.

Infected areas near a major vein are often oval in shape, while older spots develop into large, characteristic V-shaped lesions that include a leaf edge.  Dark, sunken lesions can develop on petioles.  Calyces and ripening fruits may also be infected.  The soft fruit rot caused by Phomopsis has characteristic light-pink, water-soaked to light-brown lesions, and is more serious in warmer climates.

Often Confused With
Leaf scorch
Leaf spot
Angular leaf spot

Biology
Spores are produced in pycnidia located in the centers of older leaf lesions.  High temperatures and damp weather cause these spores to ooze from the fungal bodies and splashing water enables the spores to reach new leaf tissue.  Germination occurs when there is water available on the leaf and fruit surface; the plant becomes infected.  The fungus can overwinter on infected leaves or dead tissue.

Period of Activity
Infection is found most commonly on plants after harvest.

Scouting Notes
Scout for the disease a few days after a rainy period that is followed by warm, humid weather during pre-bloom and post harvest.

Thresholds
None established.

Management Notes

  • There are no highly resistant or immune cultivars.
  • Control measures for leaf spot and leaf scorch will probably control leaf blight indirectly.
  • Choose crop management practices that keep rows narrow and encourage air flow in the row.
  • Losses caused by Phomopsis leaf blight have not been measured.