Central Maryland's tree canopy faces a range of disease and pest threats — some native, some invasive. Knowing what to look for enables early intervention, which is the difference between a treatable condition and a lost tree.
Oak Wilt
Oak wilt is a fungal disease spread by sap beetles and through root grafts between neighboring oaks. Red oaks die within weeks of infection; white oaks may survive years before succumbing. Symptoms include rapid browning from the leaf margins inward. Never prune oaks April–October — this is when beetles are active.
Anthracnose
Anthracnose is a fungal disease that affects many species — dogwood, oak, maple, sycamore. It causes brown blotches along veins, leaf curling, and early defoliation. Most established trees survive repeated infections, but repeated defoliation weakens them over time.
Fire blight is a bacterial disease that primarily affects crabapple, apple, pear, and serviceberry. It causes a distinctive scorched appearance on new growth — like the branch was held over a flame. Infected wood must be pruned well below the visible infection.
Emerald Ash Borer
EAB has killed billions of ash trees across North America. In Maryland, virtually all untreated ash trees will eventually die from EAB. Signs include D-shaped exit holes in bark, S-shaped galleries under the bark, woodpecker damage, and crown dieback. Treatment with systemic insecticides is effective if started before the tree is more than 30% dead.
Bacterial Leaf Scorch
BLS is a bacterial disease spread by leafhoppers that causes progressive leaf scorching, typically starting on one branch and spreading over years. It affects oaks, sycamore, elm, maple, and others. There is no cure — management involves maintaining tree vigor and pruning dead wood.