Hektar

Pseudomonas syringae pv. lachrymans (cucurbit angular leaf spot).

Symptoms of the Disease (Diagnosis Characteristics)

The disease caused by Pseudomonas syringae pv. lachrymans is a bacterial infection that affects cucumbers and manifests on all aerial parts of the plant, including cotyledons, leaves, stems, and fruits throughout the entire vegetation period. Key diagnostic symptoms include:

1. Cotyledons:

   • Small, angular, dark green to brown, water-soaked spots form towards the tip or spread across the entire surface.
   • The affected cotyledons often become brown, dry, and stunted in growth.

2. Leaves:

   • Angular, water-soaked dark green spots (2-7 mm) appear along the veins.
   • In high humidity conditions (above 90%), these spots enlarge and merge, covering large areas of the leaf.
   • A mucilaginous bacterial exudate may form on the underside of the leaves in wet conditions, drying into a white-gray crust.
   • Over time, the spots turn brown, the surrounding tissue dries and crumbles, leaving the leaf with perforations.
   • If the infection reaches the main vein, the leaf becomes deformed.

3. Petioles and Stems:

   • Similar symptoms, including angular spots, appear on the petioles and stems.
   • Depending on the weather (rainy or dry), the attacked tissues either rot or dry out.

4. Fruits:

   • The fruits develop small, irregular or circular spots (1-3 mm) that are dark green with a whitish center.
   • These spots eventually dry and crack, and in wet weather, they become covered with whitish bacterial exudate.

Plants suffering from this bacterial attack often exhibit stunted growth and reduced productivity.

Factors Favoring Disease Occurrence and Spread

1. Optimal Conditions:

   • Atmospheric temperatures between 18-28°C (optimum at 23°C) and humidity above 90% favor the onset and evolution of this bacterial disease.

2. Primary and Secondary Infections:

   • The bacterium is transmitted through seeds, both as an endophyte and epiphyte.
   • In the soil, the bacterium survives in plant debris for nearly a year, making the decomposition of plant tissues critical to its persistence.

3. Spread:

   • The bacterium spreads through rain, sprinkler irrigation, insects, and even via fungicide or insecticide applications meant to control other pathogens or pests in the cucumber crop.

Prevention and Control Measures

1. Cultivation Practices:

• Plant resistant or tolerant cucumber varieties or hybrids to reduce the risk of infection.
• During the vegetation period, foliar treatments should be applied both in solariums and open fields to limit secondary infections.

2. Early Intervention:

• At the stage of 1-2 true leaves, thin the plants to the recommended density, removing any that show signs of infection.
• Immediately following this thinning, apply the first foliar treatment with one of the copper-based products:
  • Funguran OH 0.2% or
  • Champion 50 WP 0.25%.
• Subsequent treatments (1-2 more) should follow at 8-10 day intervals, depending on weather conditions, as dry weather naturally inhibits disease progression.

3. Foliar Treatments:

• Copper-based fungicides provide effective control of secondary infections. Recommended products include:
  • Funguran OH 300 SC 0.15%
  • Bouille Bordelaise 0.75%
  • Melody Compact 49 WG 0.2%
  • Champ 77 WG 0.2%
  • Novozir 0.2%.

These treatments, along with good agricultural practices such as crop rotation, debris removal, and selecting disease-resistant varieties, will help control the spread of Pseudomonas syringae pv. lachrymans and maintain healthier cucumber crops.