Pennsylvania’s diverse landscape, rich with forests and urban greenery, is susceptible to several tree diseases that can significantly impact both native and ornamental tree species. Here are five of the most common tree diseases affecting trees in Pennsylvania:

1. Anthracnose: Anthracnose is a fungal disease that affects many deciduous trees, such as sycamore, oak, maple, and ash. This disease is characterized by dark, irregular blotches or lesions on leaves, and it can cause early leaf drop. It is most prevalent during cool, wet spring conditions, which provide the ideal environment for the fungus to thrive. While anthracnose rarely kills trees outright, repeated infections can weaken them over time, making them more vulnerable to other stresses.
2. Dutch Elm Disease (DED): Dutch Elm Disease, caused by the fungus Ophiostoma novo-ulmi, has devastated American elm populations across Pennsylvania. It spreads primarily through elm bark beetles or through root grafts between trees. The disease clogs the tree’s vascular system, preventing water from reaching its leaves, leading to wilting, yellowing, and eventual death, often within a single growing season. Prompt removal of infected trees and use of resistant elm varieties are key to controlling DED.
3. Oak Wilt: Oak Wilt is a severe fungal disease caused by Bretziella fagacearum that affects oaks, particularly red and live oaks. The fungus spreads through root connections or by sap-feeding beetles carrying the spores. Infected trees show symptoms such as leaf discoloration (starting from the edges), rapid leaf drop, and crown dieback. Red oaks can die within weeks, while white oaks decline more slowly. Control methods include trenching to sever root connections and removing infected trees.
4. Armillaria Root Rot: Armillaria Root Rot, also known as “honey fungus,” is a soil-borne fungal disease that affects a wide range of tree species, including oaks, maples, and birches. The fungus attacks the tree’s roots and lower trunk, causing decay and eventual death. Symptoms include yellowing leaves, dieback, and white fungal growths under the bark. Trees weakened by drought, injury, or other stressors are particularly susceptible. Proper tree care, such as avoiding injuries and providing adequate water, can help prevent this disease.
5. Apple Scab: Apple Scab is a fungal disease caused by Venturia inaequalis that primarily affects apple and crabapple trees. It is characterized by dark, olive-green spots on leaves and fruit, which can become distorted and drop prematurely. Wet, cool conditions in spring favor the spread of apple scab. While this disease does not usually kill trees, it can significantly reduce fruit quality and tree vigor. Pruning for better air circulation, removing fallen leaves, and applying fungicides can help manage apple scab.

These common diseases highlight the importance of proper tree care and early intervention to maintain the health and vitality of Pennsylvania’s trees. By identifying symptoms early and implementing appropriate management practices, tree owners can help protect the region’s valuable tree populations from these destructive diseases.