St. Louis is a climate crossroads. Its humid summers, variable winters, and wet springs create conditions that favor a wide range of fungal, bacterial, and vascular tree diseases year-round. These pathogens are worsened by the city’s increased drought conditions, construction damage, and urban stress.
Early pest and disease detection is key to saving trees. Davey’s certified arborists serving the St. Louis area are local experts homeowners can call at the first sight of trouble.
Why St. Louis Trees Are Especially Vulnerable to Disease
St. Louis is positioned at the convergence of humid subtropical and humid continental climates, creating year-round disease pressure. Urban heat island effects, compacted soils in residential areas, and the diversity of ornamental tree species planted across the metro area all contribute to susceptibility.
With disease pressure lasting year-round, knowing which ones are most common during each season can help with early detection and treatment.
Spring Tree Diseases in St. Louis: What Starts Attacking Your Trees in March and April
Spring is the highest risk window for fungal disease. Cool, wet conditions accelerate spore germination and spread, making it a critical time to inspect trees as they leaf out.
Anthracnose: Why St. Louis Sycamores, Oaks, and Maples Get Brown Blotches Every Spring
Anthracnose is one of the most misidentified diseases in St. Louis. Homeowners often confuse it with frost damage or drought stress. Commonly found on sycamores, oaks, dogwood, and maples, Anthracnose often results in:
Brown blotches along leaf veins
Irregular dead patches
Early defoliation
On sycamore and dogwood trees, anthracnose can cause serious shoot dieback and cankers over time, making it one of the most serious spring disease concerns in the St. Louis region.
Cool, wet spring weather often drives outbreaks of anthracnose. Mature trees usually recover from the disease, but repeated infections weaken them over time.
Learn more about anthracnose here.
Apple Scab in St. Louis: Why Your Tree Drops Leaves Early Every Year
Apple scab is highly visible on ornamental crabapples, which are among the most popular residential street trees in St. Louis. Symptoms of this disease often look alarming, making residents believe their trees are dying. Keep an eye out for:
Brown velvety lesions on leaves and fruit
Premature defoliation
Yellowed, curled, and puckered-looking leaves
"Susceptibility to apple scab varies widely by cultivar. Planting disease-resistant cultivars of ornamental crabapples, like Prairifire, Donald Wyman, and Adirondack, is the long-term solution for avoiding this disease."
Learn more about apple scab here.
Fire Blight in St. Louis: How to Spot the Bacterial Disease That Makes Branches Look Burned
Fire blight is a bacterial disease that spreads rapidly during warm, wet spring weather, making St. Louis’s ideal for fire blight conditions. Its bacteria multiply rapidly in blossom nectar and infect flowers through natural openings. Warm temperatures, between 60 and 75 degrees Fahrenheit, and wet conditions during bloom are the primary triggers. Symptoms of fire blight include:
“Shepherd’s crook” branch die-back
Burned appearance of new growth
Cutting out infected wood with sterilized tools is critical to containing spread.
Learn more about fire blight here.
Cedar-Apple Rust in St. Louis: Why Your Crabapple and Eastern Red Cedar Both Seem Sick at the Same Time
Rust diseases require two host plants to complete their life cycle: eastern red cedars and a rosaceous host like crabapple, hawthorn, or apple. This disease is common in St. Louis since both host species are present in residential and natural areas. Symptoms include:
Orange, gelatinous spore horns on cedar trees in spring
Yellow-orange lesions on hawthorn and crabapple leaves in the spring and summer
Learn more about cedar-apple rust here.
Cytospora Canker in St. Louis: Why Your Blue Spruce Is Dying From the Bottom Up
Cytospora canker is a stress-induced fungal disease that primarily attacks spruce trees during wet spring weather. Common stressors in St. Louis, like wounds, drought damage, or mechanical injury, can cause Cytospora canker. Symptoms include:
White resin-soaked bark
Progressive lower branch dieback, especially in Colorado blue spruces
Learn more about Cytospora canker here.
Summer Tree Diseases in St. Louis: Heat and Humidity Create a Second Wave of Challenges
Summer is the season of stress in St. Louis. High heat and humidity compound existing disease pressure, and trees weakened by spring infections become targets for additional pathogens and boring insects. Oftentimes, diseases that appear in the summer were actually contracted earlier in the year.
Oak Wilt in St. Louis: How This Vascular Disease Can Kill a Red Oak
Oak wilt is one of the most serious tree diseases in the St. Louis area. It spreads to red oaks primarily through sap-feeding beetles called nitidulids that are active from April to June and through root graft transmission between neighboring oaks. It’s important to avoid pruning oak trees from April through June and sealing wounds immediately to mitigate spread. Symptoms include:
Premature leaf drop, including leaves that are still pretty green
Rapid branch die-back, often within a single season
Partial leaf scorch that appears brown on leaf tips and green at the base
In red oaks, rapid defoliation can occur within two to six weeks of initial infection, and death occurs within a year.
"Look out for sapwood streaking in red oaks. It often appears as a brown vascular discoloration under the bark and results in rapid canopy dieback and marginal leaf browning. This is a key indicator for diagnosing oak wilt."
Learn more about oak wilt here.
Powdery Mildew on St. Louis Trees: What That White Coating on Your Dogwood Actually Means
Powdery mildew thrives in St. Louis’s humid summers and affects a wide range of trees, including dogwood, oak, and maple. While rarely fatal on its own, repeated infections weaken trees and can make them more susceptible to other diseases. Symptoms include:
White, powdery coating on leaves and new growth
Foliage discoloration and early leaf drop if not treated
Learn more about powdery mildew here.
Biscogniauxia Canker (Hypoxylon) in St. Louis: The Stress-Triggered Disease That's Always Fatal Once It Appears
Biscogniauxia canker, formerly known as Hypoxylon, is a stress-triggered disease that becomes active in trees weakened by environmental issues such as summer drought, construction damage, or soil compaction. Typically, it’s triggered by a stress event that happens a few years prior and is common in oaks and maples across the St. Louis region. It is always fatal once symptomatic. Key features of Biscogniauxia canker include:
A silver-gray to black fungal mat that develops as bark sloughs away
Outbreaks tend to follow severe drought or other stress events
Only stressed or damaged trees develop cankers and are killed by this otherwise latent fungus
"To avoid outbreaks, keep trees healthy using proper care practices, such as watering, mulching, and providing adequate nutrition."
Learn more about Biscogniauxia canker here.
Fall Tree Diseases in St. Louis: Why Autumn Is the Right Time to Assess Damage Before Winter Sets In
Fall in St. Louis is the season for assessing cumulative damage from the year and identifying diseases that will overwinter or resurface in spring. Symptoms visible in fall may reflect infections from earlier in the season, making the season a critical time for certified arborist evaluations before winter.
Armillaria Root Rot in St. Louis: What Those Honey-Colored Mushrooms at Your Tree's Base Actually Signal
Armillaria root rot is common throughout Missouri and often appears in fall. It can infect more than 200 species of hardwoods and conifers, with oaks, elms, and maples being highly susceptible. Once established, the fungi can live for years on dead roots and spread to nearby living trees, making it difficult to establish new trees in infected areas. Symptoms include:
Clusters of honey-colored mushrooms at the base of infected trees
White, fan-like fungal mats beneath the bark of the lower trunk
Progressive canopy thinning
Branch dieback
Learn more about Armillaria root rot here.
Winter Tree Disease in St. Louis: What Certified Arborists Look for During the Dormant Season
Winter is the right time to schedule preventive care and inspect tree bark for signs of cankers, gall formations, and structural problems that are easier to see without leaves. Some diseases, like oak wilt, can still spread during mild winter periods through root grafts, but winter is still the safest time to prune oak trees.
Diplodia Tip Blight on St. Louis Pine Trees
Diplodia tip blight affects Austrian pines, Scots pines, and ponderosa pines, all of which are commonly planted in St. Louis landscapes. Infections begin in late winter when spores are released from infected cones and bark, but symptoms often don’t appear until spring. Repeated infections can cause progressive dieback from the lower branches upward. Symptoms include:
Brown, stunted new shoots in spring
Dead tips with small black fruiting bodies at the base of needles
Learn more about Diplodia tip blight here.
How Davey's St. Louis Arborists Diagnose Tree Disease — Including Lab-Confirmed Testing
Davey’s science-backed diagnostic approach prevents wasted treatment costs and ensures the right intervention for each disease by ensuring accurate diagnosis.
Certified arborists assess visual symptoms, gather leaves and small branch samples for testing at the Davey Institute Diagnostic Laboratory, and consider site history to make informed decisions on disease management.
Some diseases, like oak wilt, require immediate action while others allow a broader treatment window
Let Davey Protect Your St. Louis Trees Year-Round
Davey’s certified arborists have the expertise needed to properly diagnose and treat diseases year-round. Contact your local Davey office for a free consultation.
FAQ for St. Louis Homeowners
Sycamores and maples suffer heavily from anthracnose during wet springs, while red and pin oaks face severe threats from oak wilt.
Warm, wet spring weather accelerates fungal spores, while sap-feeding beetles actively spread lethal vascular pathogens during the growing season.
Early diagnosis and treatment are the keys to tree survival. If your tree is showing signs of disease, like leaf loss or branch dieback, contact your local arborist for an inspection.
