Olive Knot: A Comprehensive Guide to Recognizing and Managing This Pervasive Disease

Olive knot is a widespread and destructive disease that affects olive trees worldwide. Its characteristic galls or “knots” can be easily identified, and yet the disease itself can be challenging to manage. Understanding olive knot, its causes, symptoms, and ways to control it, is vital for olive growers. In this in-depth blog post, we’ll delve into everything you need to know about olive knot, whether you are an avid home gardener or a commercial olive producer.

What is Olive Knot?

Olive knot is a bacterial disease caused by the pathogen Pseudomonas savastanoi pv. oleae. It primarily affects olive trees, causing abnormal growths or galls to form on branches, twigs, leaves, and sometimes even on fruit. If left unchecked, the disease can lead to reduced productivity, poor tree health, and even death of branches.

Symptoms of Olive Knot

The most prominent symptom of olive knot is the formation of galls or knots:

  • Initial Stage: Small, light-green galls appear, usually at leaf scars or wounds.
  • Mature Galls: The galls grow and become more prominent, turning dark brown or black. They may range in size from pea-sized to larger, irregular masses.
  • Leaf Curling: Affected leaves may curl and become distorted.
  • Stunted Growth: In severe cases, the growth of new shoots can be stunted, leading to a decline in tree vigor.

Causes and Spread of Olive Knot

  • Bacterial Infection: The bacterium Pseudomonas savastanoi pv. oleae is the causative agent.
  • Transmission: The bacteria can be spread by rain, pruning tools, infected plant material, or insects.
  • Entry Points: Wounds or natural openings, such as leaf scars, provide entry points for the bacteria.


While the galls are usually distinctive, professional lab testing can confirm the diagnosis. Testing might include:

  • Visual Inspection: Examining the characteristic galls.
  • Microscopic Examination: Observing bacterial streaming from infected plant tissues.
  • Culture and PCR Tests: Isolating the bacterium and identifying it through laboratory methods.

Management of Olive Knot

1. Cultural Practices

  • Pruning: Remove infected branches and twigs, well below the galls, during dry weather to minimize the spread.
  • Disinfect Tools: Regularly sanitize pruning tools to prevent transmission between trees.
  • Avoid Overhead Watering: Overhead irrigation can facilitate the spread of the bacteria.

2. Chemical Control

  • Copper Sprays: Applying copper-based fungicides during the dormant season can help reduce infection.
  • Antibiotics: Some regions may allow the use of specific antibiotics as a control measure.

3. Resistant Varieties

  • Planting Resistant Trees: If available, plant olive varieties that are known to be less susceptible to olive knot.

4. Monitoring and Early Intervention

  • Regular Inspection: Early detection and removal of infected material can reduce the spread.
  • Professional Help: Consulting with local agricultural extension services or plant pathologists can provide specific recommendations.


  • Careful Planting: Start with certified disease-free planting material.
  • Avoid Injury: Minimize wounding trees, as wounds can provide entry points for the bacteria.
  • Quarantine Measures: Follow regional guidelines for quarantining and handling infected material.

Conclusion: An Ongoing Battle with Hope

Olive knot is a formidable disease that requires ongoing vigilance and careful management. With proper cultural practices, judicious use of chemical controls, early detection, and cooperation with local agricultural authorities, it is possible to limit its impact.

Remember, understanding the disease is the first step in its management. By implementing the practices outlined in this guide, olive growers can protect their trees from this pervasive disease and enjoy healthy, productive olive orchards. Whether you are tending a single beloved tree or overseeing a vast commercial operation, awareness, and proactive care are the keys to triumphing over olive knot.