Angular leaf spot

(Pseudomonas syringae pv. lachrymans)

Credits: Biovision-Infonet

Spots on leaves angular in shape and variable in size due to leaf veins that limit their enlargement. Initially, spots are water-soaked. In moist weather, bacteria ooze from the spots in tear-like droplets, which dry making the tissue white. Affected leaf dries and shrinks, and it may tear away from the healthy portion leaving irregular holes. Leaves approaching maturity are more susceptible than older leaves. Fruits may also be attacked. Fruit spots are small, nearly circular and superficial. The bacteria survive in association with seed. When infected cucumbers are used for seed extraction, the seed can be contaminated during fermentation process. The bacteria can also survive in soil or infected crop debris. Drainage water can spread the bacteria in the soil.

Angular leaf spot disease is favoured by wet conditions, frequently associated with rainfall and overhead irrigation. Optimum temperature for disease development is 23.9 to 27.8⁰C. The disease attacks watermelon, gherkin, muskmelon, pumpkin, squash, and vegetable marrow.

What to do:

• Use resistant varieties, if available.
• Use certified disease-free seed.
• Practise crop rotation. A crop rotation of 1 to 2 years is recommended.
• Avoid run-off water from nearby cucurbit fields and overhead irrigation.