Weeping willow, known botanically as Salix, is an ornamental deciduous tree prized for its shade and elegant growth form. As a species, it is susceptible to a strain of cotton root rot caused by the fungus Phymatotrichum omnivorum. The fungus can attack the tree causing its appearance to decline or kill portions of or the entire tree over time or sometimes, fairly quickly. The symptoms of cotton root rot are most prevalent in the summer and early fall when soil temperatures have warmed above 82 degrees Fahrenheit. The fungus will persist in the soil for several years after a tree has been infected or killed.
Foliage Discoloration and Wilt
Root rot will cause the leaves of the weeping willow to change from their natural medium green tone to yellow, tan or brown starting in the upper canopy with the color change cascading down the canopy as the infection progresses. By the time the leaves become discolored, the disease is likely to be well-established.
Wilted and Dying Leaves
Weeping willow leaves in the upper canopy will begin to wilt roughly 48 hours after they turn to a sickly color. Within 72 hours after discoloration, the lower leaves can begin to show signs of wilt. The leaves will be permanently wilted and begin to die in as soon as three to four days. The dead leaves will remain attached to the branches, preserved in place even though they are dead.
Decaying Root Bark and Loose Footing in the Soil
The root bark of infected willow trees will look as though it is breaking down, turning brown in color and growing fine bronze brown hair-like strings of fungal spores that can be seen when looking at the roots. The skin of the roots will tear and slip off easily when touched. As the roots rot they lose their grip in the soil slowly making the tree unstable in the grown either in one area or eventually entirely when the tree will fall under its own weight or with a strong wind.