Common Tree Diseases & Pests

Common Diseases for Trees in St. Louis & Missouri

Trees in St. Louis are vulnerable to a number of fungal, bacterial, and environmental diseases that can compromise their appearance, weaken their structure, and even lead to tree death if left untreated. Early detection is key and while many of these diseases show subtle signs at first, but our certified arborists know what to look for. Below are some of the most common tree diseases affecting our region, along with a brief description of each.

• Anthracnose
  A fungal disease that causes irregular brown or black spots on leaves, especially during wet spring weather. It affects sycamores, oaks, dogwoods, and maples, often leading to premature leaf drop.
  
  
• Fire Blight
  A fast-spreading bacterial infection that primarily targets fruit trees like pear and crabapple. It causes blossoms, leaves, and branches to turn black and look scorched, hence the name.
  
  
• Bacterial Leaf Scorch
  Common in oaks, elms, and maples, this disease causes browning around leaf edges and early leaf drop. It slowly reduces tree vigor over several years.
  
  
• Bur Oak Blight (BOB)
  A fungal disease specific to bur oaks that leads to dark leaf spots, browning, and twig dieback, often showing up in late summer and worsening annually.
  
  
• Root Rot (Armillaria)
  Caused by fungi that thrive in overly wet or compacted soil. It weakens root systems from the inside out, often without clear above-ground symptoms until the tree is unstable or dying.
  
  
• Dogwood Anthracnose
  A severe fungal disease is impacting flowering dogwoods. It causes purple-bordered leaf spots, wilting, and dieback, especially in shaded, moist environments.
  
  
• Oak Wilt
  A deadly vascular disease that disrupts water flow in oak trees, causing sudden wilting, browning, and rapid death, particularly dangerous for red oaks.
  
  
• Apple Scab & Cedar-Apple Rust
  These fungal diseases affect apple, crabapple, and hawthorn trees. They create lesions on leaves and fruit, leading to deformity, early defoliation, and weakened health over time.
  

• Heart Rot‍
  A decay that affects the internal wood of older trees, especially maples and hardwoods. Though not always visible, it compromises structural stability and increases the risk of trunk failure.

Common Tree Pests For Trees in St. Louis & Missouri

Alongside fungal and bacterial diseases, trees in the St. Louis area also face serious threats from invasive and native insect pests. These pests can damage leaves, bark, branches, and root systems, weakening the tree and leaving it vulnerable to other problems. Some pests are simply a cosmetic issue, while others can kill a tree if left untreated. Below are the most common insect pests that affect trees in St. Louis and surrounding Missouri communities.

• Emerald Ash Borer
  ‍An aggressive, invasive beetle that has devastated ash trees across Missouri. Larvae burrow beneath the bark, cutting off the tree’s ability to move water and nutrients. Infected trees often die within a few years without treatment.
  

• Oak Gall Wasps
  Tiny wasps that lay eggs on oak trees, causing the tree to form abnormal growths called galls on leaves, twigs, or branches. While typically not fatal, heavy infestations can cause stress, branch dieback, and aesthetic damage.
  
  
• Bagworms
  These pests build silk bags covered in bits of leaves and twigs and feed on the foliage of evergreens and deciduous trees. Large populations can defoliate and severely weaken trees, especially arborvitae, spruce, and juniper.
  
  
• Japanese Beetles
  Metallic green beetles that skeletonize leaves of trees like lindens, elms, and crabapples. Damage peaks in midsummer and can reduce a tree’s ability to photosynthesize effectively.
  
  
• Scale Insects
  These small, sap-sucking insects attach themselves to bark or leaves and can cause yellowing, leaf drop, and stunted growth. Heavy infestations often go unnoticed until trees show signs of stress.
  
  
• Caterpillars and Cankerworms
  Various leaf-chewing larvae feed on a wide range of trees in the spring and early summer. While a healthy tree can recover from defoliation, repeated attacks can lead to long-term damage.
  
  
• Aphids
  Tiny insects that cluster on new growth and suck sap from leaves and stems. They produce a sticky residue called honeydew that can lead to mold growth and attract other insects.
  

• Boring Insects (e.g., Bark Beetles)
  These pests tunnel into the bark and cambium layer of stressed or weakened trees, disrupting nutrient flow and introducing fungi. Common in declining oaks and conifers.

Common Trees in St. Louis and Common Problems They Face

St. Louis is home to a beautiful mix of native hardwoods, ornamentals, and evergreen trees. Each species has its strengths, but they also face unique challenges depending on the local climate, soil conditions, and their natural resistance to pests or disease. Below is a list of some of the most common trees you'll find in the St. Louis area, along with the most frequent problems we see affecting each.

• Red Maple
  A fast-growing shade tree popular in residential areas. Prone to anthracnose, verticillium wilt, leaf scorch, and girdling roots. Aphids and scale insects can also be a concern.
  
  
• Pin Oak
  Commonly planted for its upright shape and fast growth. Vulnerable to bacterial leaf scorch, oak wilt, iron chlorosis (especially in alkaline soil), and oak gall wasps.
  
  
• Sugar Maple
  Known for brilliant fall color, but sensitive to heat and compacted urban soil. Susceptible to verticillium wilt, anthracnose, tar spot, and leaf scorch.
  
  
• Dogwood (Flowering Dogwood)
  A St. Louis favorite for spring blooms. Frequently affected by dogwood anthracnose, powdery mildew, borers, and leaf spot, especially when planted in shaded or moist areas.
  
  
• Eastern Redbud
  A small, ornamental tree often used in landscaping. Common issues include canker diseases, verticillium wilt, and leaf spot. Caterpillars and borers may also appear.
  
  
• White Oak & Bur Oak
  Native hardwoods with great shade value. Susceptible to oak wilt, bur oak blight, bacterial leaf scorch, and heavy oak gall infestations. Also at risk of root rot in poorly drained soil.
  
  
• Bradford Pear (Callery Pear)
  Once widely planted but now considered invasive in Missouri. Prone to fire blight, leaf spot, and limb breakage due to weak branching structure.
  
  
• Sycamore
  Common in parks and older neighborhoods. Often impacted by anthracnose (causing leaf drop and twig dieback), powdery mildew, and sycamore lace bugs.
  
  
• Ash (Green & White Ash)
  Ash trees have been devastated across Missouri by the emerald ash borer. Once infested, decline is rapid without immediate treatment.
  
  
• Elm (American Elm & Hybrids)
  Once a staple of city streets. Still vulnerable to Dutch elm disease and elm leaf beetles, although newer cultivars are more resistant.
  

• Eastern White Pine & Spruce (Evergreens)
  Used as privacy screens and windbreaks. Can suffer from needle cast diseases, bagworms, tip blight, and aphid infestations in dense plantings.

• Oak Gall Wasps
  Tiny wasps that lay eggs on oak trees, causing the tree to form abnormal growths called galls on leaves, twigs, or branches. While typically not fatal, heavy infestations can cause stress, branch dieback, and aesthetic damage.
  
  
• Bagworms
  These pests build silk bags covered in bits of leaves and twigs and feed on the foliage of evergreens and deciduous trees. Large populations can defoliate and severely weaken trees, especially arborvitae, spruce, and juniper.
  
  
• Japanese Beetles
  Metallic green beetles that skeletonize leaves of trees like lindens, elms, and crabapples. Damage peaks in midsummer and can reduce a tree’s ability to photosynthesize effectively.
  
  
• Scale Insects
  These small, sap-sucking insects attach themselves to bark or leaves and can cause yellowing, leaf drop, and stunted growth. Heavy infestations often go unnoticed until trees show signs of stress.
  
  
• Caterpillars and Cankerworms
  Various leaf-chewing larvae feed on a wide range of trees in the spring and early summer. While a healthy tree can recover from defoliation, repeated attacks can lead to long-term damage.
  
  
• Aphids
  Tiny insects that cluster on new growth and suck sap from leaves and stems. They produce a sticky residue called honeydew that can lead to mold growth and attract other insects.
  

• Boring Insects (e.g., Bark Beetles)
  These pests tunnel into the bark and cambium layer of stressed or weakened trees, disrupting nutrient flow and introducing fungi. Common in declining oaks and conifers.

Common Trees in St. Louis and Common Problems They Face

St. Louis is home to a beautiful mix of native hardwoods, ornamentals, and evergreen trees. Each species has its strengths, but they also face unique challenges depending on the local climate, soil conditions, and their natural resistance to pests or disease. Below is a list of some of the most common trees you'll find in the St. Louis area, along with the most frequent problems we see affecting each.

• Red Maple
  A fast-growing shade tree popular in residential areas. Prone to anthracnose, verticillium wilt, leaf scorch, and girdling roots. Aphids and scale insects can also be a concern.
  
  
• Pin Oak
  Commonly planted for its upright shape and fast growth. Vulnerable to bacterial leaf scorch, oak wilt, iron chlorosis (especially in alkaline soil), and oak gall wasps.
  
  
• Sugar Maple
  Known for brilliant fall color, but sensitive to heat and compacted urban soil. Susceptible to verticillium wilt, anthracnose, tar spot, and leaf scorch.
  
  
• Dogwood (Flowering Dogwood)
  A St. Louis favorite for spring blooms. Frequently affected by dogwood anthracnose, powdery mildew, borers, and leaf spot, especially when planted in shaded or moist areas.
  
  
• Eastern Redbud
  A small, ornamental tree often used in landscaping. Common issues include canker diseases, verticillium wilt, and leaf spot. Caterpillars and borers may also appear.
  
  
• White Oak & Bur Oak
  Native hardwoods with great shade value. Susceptible to oak wilt, bur oak blight, bacterial leaf scorch, and heavy oak gall infestations. Also at risk of root rot in poorly drained soil.
  
  
• Bradford Pear (Callery Pear)
  Once widely planted but now considered invasive in Missouri. Prone to fire blight, leaf spot, and limb breakage due to weak branching structure.
  
  
• Sycamore
  Common in parks and older neighborhoods. Often impacted by anthracnose (causing leaf drop and twig dieback), powdery mildew, and sycamore lace bugs.
  
  
• Ash (Green & White Ash)
  Ash trees have been devastated across Missouri by the emerald ash borer. Once infested, decline is rapid without immediate treatment.
  
  
• Elm (American Elm & Hybrids)
  Once a staple of city streets. Still vulnerable to Dutch elm disease and elm leaf beetles, although newer cultivars are more resistant.
  

• Eastern White Pine & Spruce (Evergreens)
  Used as privacy screens and windbreaks. Can suffer from needle cast diseases, bagworms, tip blight, and aphid infestations in dense plantings.