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Bacterial leaf spot

Scientific name: Pseudomonas spp.
Causal organisms: Bacteria
Important species:

  • Bacterial leaf spot of cole (P. syringae pv. maculicola)
  • Bacterial leaf spot of cucurbits, Angular leaf spots (P. syringae pv. lachrymans)
  • Chocolate spot, Bacterial brown spot of beans (P. syringae pv. syringae)
  • Chocolate spot of corn (P. syringae pv. coronafaciens)
  • Host plants

    Cucurbits, beans, cereals and many other plants

    Affected plant stages

    All growth stages

    Affected plant parts

    Leaves, stems, fruits, pods, seeds


    Bacterial leaf spot of cole crops

    Infected leaf has small dark spots and as the disease develops, plenty of watersoaked leaf spots appear. The spots remain small and are visible on both sides of the leaf. When they become older, they have tan color and may or may not have purple borders

    Bacterial leaf spot of cucurbits; Angular leaf spots

    Infected leaf has initially small and nearly circular yellow spots that eventually enlarge to irregular, water-soaked areas. The underside of the leaf has dried whitish crusts of bacterial discharges which the bacteria emit during wet weather. As the bacteria progress, the infected areas turn gray, die and shrink, often torn and leaving large irregular holes on the leaf. Infected fruit shows small, almost circular spots that are usually superficial, but when the infected tissues die, the spots turn white and cracked-open. Other pathogens may enter the wound and rot the whole fruit. Infection on young fruits causes deformation and extensive fruit drop.

    Bacterial leaf spot of pepper

    Infected leaf develops small spots that later turns yellow and drops. The leaf spots are at first small, yellow-green lesions with a watersoaked border. They may join together, giving a blighted appearance. Eventually, they turn brown and dry up, leaving holes and showing a tattered look. Corky lesions develop on fruits.

    Chocolate spot, Bacterial brown spot of beans

    Infected leaf has ovate-shaped spots of dead tissues surrounded with yellow-green to lemon-yellow margins. As the spots enlarge, they may join together often having torn out dead tissues, developing a shot-hole appearance. An infected pod has initially tiny water-soaked spots that later enlarge and join together, become sticky, and develop tiny crusty area on its center during rainy days. Later, the infected area turns brown and dies causing the pod to twist or bend.

    Chocolate spot of corn

    Infected leaf has elongate dark-brown streaks, about 3 cm long surrounded by thick yellow margins found near the leaf margin or near the tip. As the spots joined together, the plant gives a blighted (dried but not rotten) appearance.

    Conditions that favor development

    1. Warm temperature, frequent rain, and high relative humidity
    2. Diseased-seeds and planting materials
    3. Over-crowded plants with poor air flow and low sunlight penetration among plants
    4. Improper soil nutrient and irrigation management
    5. Poor soil drainage

    Preventive control

    1. Rotate crops
    2. Heat water seed treatment
    3. Use diseased-free seeds or use resistant cultivars
    4. Removal and proper disposal of infected plants. Burn infected plant tissues when possible.
    5. Clean contaminated equipment
    6. Avoid working when plants are wet
    7. Mint extract

    External links


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