Watermark disease is caused by the bacterium (Brenneria salicis).
Watermark disease is caused by the bacterium (Brenneria salicis). This bacterium causes a blockage of the wood vessels, causing leaves and branches to dry out and ultimately the tree to die.
The first symptoms are summer browning of the tree’s outer leaves, after which they die. Affected branches show watery reddish-brown tree sap. The disease process is slow, with the tree becoming progressively weaker. Dried branches can easily break off in strong winds or storms.
Watermark disease mainly affects trees older than 10 years.
Infested wood release infected moisture that can infect other trees. Rain and wind also spread the bacteria.
Where to find
- Willow
- White willow (Salix alba) in particular
Control
Remove affected branches. Best to burn these – not on the compost heap or kerbside garden / food waste bin (contamination hazard).
Prevention
Do not replant areas where willows affected by watermark disease have stood with willows.
