Wilt

Wilt diseases are caused by pathogens that colonize and block the vascular (water-conducting) system of trees. As the xylem vessels become clogged with fungal growth, bacterial masses, or the tree's own defensive tyloses, water can no longer reach the canopy, causing progressive wilting, leaf scorch, and branch death. Wilt diseases are among the most serious tree ailments because they attack the fundamental transport system.

Major wilt diseases include Dutch elm disease (caused by Ophiostoma fungi spread by bark beetles), oak wilt (caused by Bretziella fagacearum), verticillium wilt (caused by Verticillium species affecting many tree species), and laurel wilt (caused by Raffaelea lauricola spread by ambrosia beetles). Each has specific hosts, vectors, and management approaches.

Diagnosis of wilt diseases often involves checking for vascular discoloration. Cutting into affected branches typically reveals dark streaking in the sapwood as the pathogen colonizes the xylem. Laboratory culture or molecular testing may be needed for definitive identification. Treatment options vary by disease but may include fungicide trunk injections, disrupting root graft connections between trees to prevent underground spread, and removing infected trees to reduce inoculum. For some wilt diseases, there is no cure, and management focuses on prevention and containing spread.