As autumn arrives in St. Louis and St. Charles, your trees’ vibrant foliage may be the envy of your neighborhood. But beneath those beautiful leaves, several pests are making their moves, ready to feast on your hardwoods and evergreens. Read one to learn about the most common fall invaders, how to spot them, and how to protect your trees, shrubs and landscaping with proper care.

Fall Webworms – The Fuzzy Foliage Intruders Invading the St. Louis Area

What to look for: Late summer through fall, you may spot swollen, silken nests (sometimes two or more feet across) on branch tips closely tied together with webbing. Inside, fall webworm caterpillars feed on leaves until they’re nearly skeletal.

Trees affected: Hickory, walnut, persimmon, pecan, and more than 120 hardwood species are susceptible.

Impact: Mostly aesthetic. Healthy large trees typically recover easily. However, intense infestations on young or small trees may weaken them.

What you can do:

• Manually prune out webs and drop them into soapy water.
• Or tear them open to allow natural predators like birds and wasps to help.
• In severe cases, treat early with bacillus thuringiensis or spinosad.

Fall Cankerworms – The Subtle Leaf Skeletonizers Common to St. Louis and St. Charles

What to look for: Tiny inch‑worms chewing holes or skeletonizing leaves, often starting in spring but occasionally noticeable in early fall. The larvae feed until mid‑season, dropping to the ground to pupate.

Trees affected: Oaks, hickories, ash, elm, basswood, maple, apple, and more.

Impact: Outbreaks can defoliate trees, causing stress or weakened condition over several years, especially in repeated infestations.

Prevention and control:

• Handpick larvae if possible.
• Encourage parasitic wasps to naturally reduce populations.

Bagworms – The Tiny Travelers in Mini Silk Tents

What to look for: Small, spindle‑shaped silk bags dangling from branches, made from leaves, twigs, and debris, that house feeding caterpillars.

Trees affected: Juniper, arborvitae, cedar, maple, elm, oak, apple, and more than 100 other species.

Impact: Severe infestations strip foliage and can kill small trees or shrubs if not controlled.

Control tips:

• In fall, remove and destroy the brown bags from fall and winter before larvae hatch in spring.
• Early infestations can be treated with bacillus thuringiensis, spinosad, or other targeted insecticides.

Scale Insects and Spider Mites – The Sap Suckers

While not always obvious, sap-feeding insects can leave lasting effects, even in fall.

• Scale insects (walnut scale or oystershell scale): Form small, dome-like bumps on branches, often causing yellowing, stunted foliage, and sticky residue.
• Tulip and Magnolia Scale: A major fall pest. Look for black, shiny material (sooty mold) on the foliage, an overall unthrifty appearance, and swarming bees, wasps, or hornets attracted to the honeydew they excrete._
• Spruce spider mites: Fine webbing on needles and yellowing often signal their presence, particularly on evergreens like arborvitae, fir, and spruce.  

Control advice:

• Monitor for presence in fall.
• Treat infestations during crawler stages with horticultural oils or insecticidal soaps.

Invasive Pests on the Radar, throughout Missouri

Missouri faces threats from several dangerous non-native invaders that can disrupt even healthy landscapes:

• Asian Longhorned Beetle: Attacks maples and other hardwoods, leaving round exit holes and sawdust.
• Spongy Moth (Formerly Known as the Gypsy Moth): Strips leaves from oaks and other trees; look for fuzzy egg masses on bark or vehicles.
• Spotted Lanternfly: Prefers maple, but feeds on many trees and vines. They often travel on smooth surfaces, making them easy hitchhikers. Removing their mud-like egg masses helps curb spread.

What to do: Report sightings to local authorities such as the Missouri Department of Conservation. Scrape off and properly dispose of egg masses to help prevent introduction and spread.

Fall Foes at a Glance

Pest	Signs	Threat Level	Best Response
Fall Webworms	Webs at branch tips	Low (aesthetic)	Prune/remove webs or treat early
Fall Cankerworms	Skeletonized leaves	Medium to high	Handpick, encourage natural predators
Bagworms	Debris bags hanging on limbs	High (if unchecked)	Remove bags, early treatment
Scale & Spider Mites	Sticky/honeydew residue, webbing	Medium	Monitor, treat crawler stages
Invasive Species (e.g., ALB, SLF, Gypsy Moth)	Egg masses, holes, feeding damage	High, landscape-altering	Report, remove eggs, professional help

 

Why Early Fall Monitoring Matters Throughout the St. Louis Region

The St. Louis and St. Charles areas experience a seasonal shift; summer warmth slows, insects move in, and your trees shift energy from foliage to roots. Fall is a vital time to scout and act:

• Identifying pests early allows targeted, effective responses before damage worsens.
• Many infestations are more cosmetic than harmful, but smaller or young trees may not bounce back without care.
• Integrated pest management practices, like hand-removal, encouraging beneficial insects, or light treatments, can reduce chemical use and protect local ecosystems.

How Hansen’s Tree Service Can Help You This Fall

Don’t go it alone. Hansen’s Tree Service offers:

• Fall tree inspections for pests and health hazards across the St. Louis, St. Charles, and Lake of the Ozarks areas.
• Safe, species‑appropriate treatments (organic or conventional as needed), including removal of webs, bags, egg masses, and more.
• Integrated care, including mulching, watering plans, pruning, and monitoring, for long-term tree health.

Have you Spotted Pests or Need Advice this Fall?

Let us protect your trees, so your landscape stays vibrant and resilient this season and beyond. Contact us; we’re here to help!