Ceratocystis wilt of elms

Pathogen and Disease Type
The causal agent is the ascomycete fungus Ceratocystis smalleyi. It is a specialized pathogen that triggers vascular wilt in deciduous trees. By colonizing the xylem vessels, the fungus disrupts the upward movement of water and minerals, eventually leading to the death of the host tissue.

Susceptible Hosts
The disease primarily affects species of the genus Ulmus (elms). It is particularly notable for its impact on American elm populations. The fungus often targets trees that are stressed by environmental factors, poor site conditions, or previous physical injuries to the bark.

Symptoms and Signs
The most characteristic symptom is the wilting and yellowing of foliage, often appearing in specific sections of the canopy. Internally, a diagnostic sign is the presence of brown or dark discoloration in the sapwood, which can be seen as streaking or ring-like patterns when a branch is cross-cut.

Conditions for Development
The development of Ceratocystis smalleyi is favored by moisture and temperature regimes that support fungal growth. The disease spreads through natural root grafts between nearby trees or via insect vectors that wound the bark and introduce fungal spores into the vascular system of a healthy host.

Harmfulness and Management
This disease is highly destructive as it can kill a mature tree within a short period once the vascular system is heavily compromised. Essential management strategies include:

• Systematic monitoring and removal of infected branches or whole trees.
• Safe disposal of diseased material to prevent the spread of spores.
• Management of insect populations that may serve as vectors.
• Avoiding mechanical damage to the trunk and root zone during landscaping.