Effective Control Methods for Bacterial Soft Rot in Calla and Arum Lilies

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Calla lilies (Zantedeschia spp.) and Arum lilies are popular ornamental plants known for their striking appearance. However, these plants are susceptible to bacterial soft rot, a disease that can devastate crops if not managed properly. This comprehensive guide explores effective methods for controlling bacterial soft rot in Calla and Arum lilies through pathogen exclusion, elimination, and removal.

Understanding Bacterial Soft Rot

Bacterial soft rot is caused by bacteria that infect the plant tissues, leading to decay and rotting. This disease thrives in warm, moist conditions and can spread rapidly, causing significant damage to both the aesthetic and structural integrity of the plants.


  • Initial Signs: The first signs of bacterial soft rot include water-soaked lesions on the leaves and stems.
  • Advanced Symptoms: As the disease progresses, the infected areas become soft and mushy, emitting a foul odor. The plant may collapse as the tissues break down.

Pathogen Exclusion

Prevention Through Sanitation

  • Sterile Tools: Always use sterilized tools when handling Calla and Arum lilies. This includes pruning shears, knives, and any other instruments that come into contact with the plants.
  • Clean Growing Medium: Use sterile potting soil and avoid reusing old soil that may harbor pathogens.

Environmental Control

  • Moisture Management: Since bacterial soft rot thrives in moist conditions, manage moisture levels carefully. Avoid overwatering and ensure that the plants have good drainage.
  • Humidity Control: In greenhouse environments, control humidity levels to reduce the risk of disease spread. Use fans or ventilation systems to maintain airflow and prevent stagnant, moist air.

Pathogen Elimination

Chemical Treatments

  • Bactericides: Apply bactericides specifically formulated for ornamental plants. These can help reduce the bacterial load on the plants and prevent the spread of the disease.
  • Preventative Sprays: Use copper-based sprays as a preventative measure. These sprays can create a protective barrier on the plant surfaces, reducing the likelihood of bacterial infection.

Biological Control

  • Beneficial Microorganisms: Introduce beneficial microorganisms into the soil that can outcompete or inhibit the pathogenic bacteria. These can include certain strains of Bacillus and Trichoderma.
  • Natural Extracts: Utilize natural plant extracts with antibacterial properties, such as neem oil or garlic extract, to reduce bacterial populations on the plants.

Pathogen Removal

Removal of Infected Plants

  • Early Detection: Regularly inspect plants for signs of bacterial soft rot. Early detection and removal of infected plants can prevent the disease from spreading.
  • Disposal: Remove and destroy infected plant material away from the growing area. Do not compost infected plants, as this can spread the bacteria to other plants.

Pruning and Disposal

  • Pruning: Prune away any affected parts of the plant immediately. Make clean cuts well below the infected area to ensure that all diseased tissue is removed.
  • Sanitation: Disinfect pruning tools after each cut to prevent the spread of bacteria to healthy parts of the plant or other plants.

Best Practices for Prevention

Cultural Practices

  • Crop Rotation: Rotate crops in the growing area to prevent the buildup of pathogens in the soil. Avoid planting susceptible plants in the same location consecutively.
  • Proper Spacing: Ensure proper spacing between plants to promote air circulation and reduce humidity around the plants.

Regular Monitoring

  • Inspection: Conduct regular inspections of the plants, focusing on the base of the stems and areas where moisture tends to accumulate.
  • Record Keeping: Keep detailed records of any disease outbreaks, treatments applied, and the outcomes. This can help in identifying patterns and improving management practices.


Effective management of bacterial soft rot in Calla and Arum lilies involves a combination of pathogen exclusion, elimination, and removal strategies. By implementing these practices, gardeners and growers can significantly reduce the incidence and impact of this destructive disease. Regular monitoring, proper sanitation, and the use of both chemical and biological controls are key to maintaining healthy, vibrant lilies.

By adhering to these guidelines, you can protect your Calla and Arum lilies from bacterial soft rot, ensuring they thrive and continue to add beauty to your garden or landscape.

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