Common Tree Pests, Diseases, and Problems

Emerald Ash Borer (EAB) is an invasive beetle that kills ash trees within a few years. Signs include canopy thinning, trunk sprouts, bark splits, D-shaped exit holes, S-shaped larval tunnels, and woodpecker damage.
Emerald ash borer (EAB) Factsheet

Two-Lined Chestnut Borer (TLCB) is a native beetle that attacks stressed oaks and other hardwoods, especially after drought. It causes canopy thinning, branch dieback, and gradual tree death. Look for D-shaped exit holes, S-shaped larval galleries beneath bark, and crown dieback starting at the top. Working to eliminate environmental stressors will help mitigate this pest.
Two-lined Chestnut Borer Fact Sheet

Diseases

Oak Wilt is a serious fungal disease that spreads rapidly killing red oaks within weeks and affecting white oaks more slowly. Symptoms include rapid leaf wilting, browning from the leaf edges inward, premature leaf drop, and branch dieback. Avoiding pruning during the growing season to prevent spread of disease and remove infected trees.
Oak Wilt Factsheet (PDF)

Crabapple trees are commonly affected by various diseases such as apple scab, fire blight, and powdery mildew. Apple scab causes dark, velvety spots on leaves and fruit, often leading to early leaf drop. Fire blight is a bacterial infection that blackens blossoms, shoots, and branches, giving them a “burned” appearance. Powdery mildew produces a white, powdery coating on leaves, shoots, and buds, stunting growth. Proper sanitation, pruning, and planting disease-resistant varieties can help manage these problems.
Crabapple Diseases Factsheet (PDF)

Spruce are often impacted by several insects, fungal diseases, and environmental stress. Spruce budworms, aphids, and spider mites can damage needles and reduce growth. Fungal diseases like Rhizosphaera needle cast and cytospora canker cause needle browning, branch dieback, and cankers on the trunk. Environmental stresses such as drought, soil compaction, or winter injury can weaken trees, making them more susceptible to pests and disease. Proper site selection, watering, and monitoring can help prevent these issues.
Common Spruce Problems

Girdling Roots occur when roots encircle the trunk or other roots, constricting nutrient and water flow. This can lead to stunted growth, canopy decline, and eventual tree death. Signs include a “flared” trunk at the base, uneven growth, or roots visible above or circling the soil surface. Prevention involves careful planting, proper root pruning when necessary, and avoiding deep planting that encourages roots to circle.
Girdling Roots Factsheet