Willow Leaf and Twig Spot: Marssonina Fungus Management

A weeping willow shows brown spots on new growth (leaves and branches). Owner asks if it's a disease and how to treat.

Diagnosis: Marssonina Leaf/Twig Spot

Fungal disease (Marssonina spp.) favored by wet spring weather. Symptoms:

• Small brown-black irregular spots on leaves/twigs
• White centers with spore masses (visible in moisture)
• Twig lesions can kill small branches
• Primarily aesthetic—rarely threatens tree health

Cultural Management

• Rake and destroy fallen leaves all season, especially fall
• Prune out dead/diseased twigs (impractical on large trees)
• Improve air circulation if possible

Fungicide Option (If Warranted)

Bordeaux mixture (6-6-100) applied 2-3 times starting at leaf emergence, 10-14 day intervals. Generally not recommended for large landscape willows—disease is cosmetic.

Bottom Line

Monitor. The tree will outgrow it as weather dries. Focus on overall vigor: water during drought, mulch, avoid unnecessary stress.