Willow Scab: Symptoms, Causes, Treatment, and Prevention

Willow scab is a destructive fungal disease that primarily targets willow trees, although it can also affect other members of the Salicaceae family. The disease, caused by the fungus Venturia saliciperda, can be severely detrimental to the health of a tree if left unchecked. This in-depth guide explores the symptoms, causes, treatments, and preventative measures for willow scab.

Symptoms of Willow Scab

Willow scab presents itself in various ways, often making it challenging to diagnose. Here’s a rundown of the common symptoms:

  1. Leaf Lesions: Early symptoms include small, dark spots on the leaves. As the disease progresses, the lesions enlarge, turning into oily-looking, black spots.
  2. Leaf Curling and Wilting: Infected leaves often curl and wilt. Severe infections can cause premature leaf drop.
  3. Twig Infections: The fungus can infect young shoots and twigs, leading to dieback and causing a distorted appearance.
  4. Defoliation: Severe infections can lead to widespread defoliation, weakening the tree and reducing its growth and vigor.
  5. Secondary Infections: Infected tissues can serve as entry points for other pathogens, leading to secondary diseases like black canker.

Causes and Spread of Willow Scab

  1. Fungus Origin: The fungus Venturia saliciperda causes willow scab. Spores produced by the fungus can spread to other plants through wind, rain, or human activity.
  2. Weather Conditions: Humid and wet weather conditions are highly favorable for the development and spread of the disease. Rain and overhead irrigation can aid the spread of spores to healthy tissues.
  3. Poor Air Circulation: Densely planted willows with poor air circulation can create a microclimate that favors fungal growth.
  4. Infected Tools: Pruning tools that have been used on infected trees without proper sanitization can spread the disease to healthy trees.

Treatment of Willow Scab

  1. Pruning: Prune infected branches and twigs during the dormant season, being sure to sanitize tools between cuts.
  2. Fungicides: Application of appropriate fungicides can help control the disease. Consult a local horticulturist or tree specialist for specific recommendations.
  3. Improved Watering Practices: Avoid overhead watering, as it can spread the disease. Instead, use drip irrigation or water the soil directly.
  4. Regular Monitoring: Regularly inspect trees for signs of infection, particularly during wet seasons.

Preventive Measures

  1. Plant Resistant Varieties: If available, choose willow varieties that are resistant to scab.
  2. Proper Spacing: Plant trees with adequate spacing to ensure good air circulation, reducing the likelihood of fungal growth.
  3. Site Selection: Choose a planting site with well-draining soil to minimize standing water, which encourages fungal development.
  4. Sanitize Tools: Always sanitize pruning tools between use on different trees to prevent cross-contamination.
  5. Proper Disposal: Dispose of infected plant material properly, as it can harbor spores that could reinfect the tree or spread to others.


Willow scab is a formidable adversary for willow trees, but understanding its symptoms, causes, and the measures to treat and prevent it can go a long way in managing this disease. Regular monitoring, appropriate cultural practices, and preventive strategies are key to maintaining healthy willow trees.

By taking a holistic approach and integrating these strategies, gardeners, arborists, and homeowners can ensure that their willow trees remain vigorous, beautiful, and free of willow scab. Collaboration with local horticulture experts and following region-specific guidelines can further assist in managing this disease effectively.