ISA Certified Arborist Practice Exam

Which of the following is a common disease affecting trees?

1. Root rot

2. Black spot fungus

3. Dutch elm disease

4. Powdery mildew

The correct answer is: Dutch elm disease

Dutch elm disease is a significant tree disease caused by a fungus that is spread by bark beetles. It specifically targets elm trees, leading to their decline and eventual death. This disease is notable for its historical impact, having devastated elm populations across many regions, particularly in urban areas where these trees were once prevalent. Understanding Dutch elm disease is crucial for arborists and tree care professionals, as it requires knowledge of vector management, identification of symptoms, and appropriate disease management practices. Recognition of the early signs, such as wilting leaves and dark streaks in the xylem, is essential for managing and mitigating its spread. While the other options—root rot, black spot fungus, and powdery mildew—are indeed diseases that affect trees and plants, Dutch elm disease stands out due to its specific fungal infection and its significant ecological and aesthetic impact on urban forestry.