Common Tree Diseases and How to Spot Them
Healthy trees are one of the most valuable assets on any commercial property. They provide shade, improve air quality, enhance curb appeal, and contribute to a welcoming environment for employees, customers, tenants, and visitors. However, trees are susceptible to a variety of diseases that can compromise their health, create safety hazards, and lead to costly removals if left untreated.
Early detection is key. By recognizing the warning signs of common tree diseases, property managers and business owners can take action before minor issues become major problems. Here's what to look for.
Anthracnose
Anthracnose is a group of fungal diseases that commonly affects hardwood trees such as sycamores, maples, oaks, ash, and dogwoods during cool, wet spring weather.
Signs to Watch For
Brown or black spots along leaf veins
Curled or distorted leaves
Premature leaf drop
Dead twigs on lower branches
Sparse canopy growth
Although anthracnose rarely kills mature trees, repeated infections can weaken them over time and increase their susceptibility to other pests and diseases.
Powdery Mildew
Powdery mildew is one of the easiest tree diseases to identify because of its distinctive white appearance. It commonly affects crape myrtles, oaks, dogwoods, magnolias, and many ornamental trees.
Signs to Watch For
White or gray powdery coating on leaves
Distorted or curled new growth
Reduced leaf size
Premature leaf drop
While powdery mildew is often more cosmetic than life-threatening, severe infections can reduce tree vigor and affect overall appearance.
Leaf Spot Diseases
Many fungal and bacterial pathogens cause leaf spot diseases, which affect a wide range of ornamental and shade trees.
Signs to Watch For
Brown, black, or tan spots on leaves
Yellow halos surrounding leaf spots
Premature leaf drop
Thinning canopy
Leaf spot diseases are often more noticeable during periods of prolonged rainfall or high humidity.
Canker Diseases
Cankers are localized areas of dead bark and wood caused by fungi or bacteria entering through wounds, pruning cuts, or damaged bark.
Signs to Watch For
Sunken or cracked bark
Dead branches
Oozing sap
Discolored bark
Sections of the canopy dying back
As cankers expand, they can restrict the movement of water and nutrients throughout the tree, eventually causing branch or tree failure.
Root Rot
Root rot develops when soil remains excessively wet for long periods, allowing soilborne fungi to attack root systems.
Signs to Watch For
Wilting despite adequate watering
Yellowing leaves
Slow growth
Branch dieback
Mushrooms growing near the tree base
Soft or decaying roots
Because symptoms often appear only after significant root damage has occurred, prevention through proper drainage is especially important.
Dutch Elm Disease
Dutch elm disease is a destructive fungal disease spread primarily by elm bark beetles. It has devastated elm populations throughout North America.
Signs to Watch For
Yellowing leaves on individual branches
Leaves turning brown and curling
Branch dieback beginning near the top of the tree
Rapid canopy decline
Prompt removal of infected trees can help reduce the spread to nearby elms.
Oak Wilt
Oak wilt is a serious fungal disease that affects many oak species, particularly red oaks, and spreads through interconnected root systems and insect activity.
Signs to Watch For
Leaves browning from the edges inward
Premature leaf drop
Rapid canopy thinning
Branch dieback
Sudden tree decline
Because oak wilt spreads quickly, early diagnosis is essential for protecting surrounding trees.
Fire Blight
Fire blight primarily affects ornamental trees in the rose family, including crabapples, pears, and hawthorns.
Signs to Watch For
Blackened leaves that appear scorched
Shepherd's crook-shaped shoots
Oozing amber-colored sap
Dead blossoms and twigs
Fire blight spreads most readily during warm, humid spring weather.
General Warning Signs of Tree Disease
Not every unhealthy tree has a specific disease, but these symptoms often indicate that professional evaluation is needed:
Dead or dying branches
Sudden leaf loss outside normal seasonal changes
Yellowing or discolored foliage
Cracks in the trunk
Mushrooms growing at the base
Excessive deadwood
Peeling or loose bark
Unusual swelling or growths
Leaning trees with exposed roots
Regular inspections help identify these issues before they become safety concerns or require costly removal.
Preventing Tree Diseases
While not every disease can be prevented, proper tree care significantly reduces risk.
Healthy landscape management practices include:
Mulching correctly (2–3 inches deep, avoiding contact with the trunk)
Watering during extended dry periods
Pruning dead or damaged branches
Avoiding injuries from mowing and string trimming equipment
Improving soil health
Monitoring trees throughout the growing season
Scheduling routine professional inspections
Trees that experience less environmental stress are generally better equipped to resist disease.
Why Choose Yardnique?
At Yardnique, we know that healthy trees are essential to a beautiful and functional landscape. Our experienced commercial landscape professionals work hard to keep properties looking their best. When we, or our clients, spot potential concerns, we address them immediately to reduce costly damage while protecting the long-term health of trees and landscapes.