Oak Wilt and Fall Webworms: Identifying and Treating Illinois Tree Threats This Fall

As summer winds down and fall arrives in Illinois, trees begin to show seasonal changes that signal the transition to cooler weather. Unfortunately, some signs homeowners notice in September and October aren’t just natural autumn color shifts—they may be indicators of pests and diseases. Two of the most common late-season problems we see at Homer Tree Care are oak wilt and fall webworms. Both can cause stress to your trees, though in very different ways. Here’s what you need to know to keep your landscape healthy this fall.

Oak Wilt: A Serious Threat to Oaks

What it is:

Oak wilt is a lethal fungal disease that affects oaks throughout Illinois and the Midwest. The fungus, Bretziella fagacearum, spreads quickly, either underground through root grafts between neighboring trees or aboveground via sap-feeding beetles.

What to watch for in fall:

• Rapid leaf wilting and bronzing, often starting at the top of the canopy.
• Sudden leaf drop, sometimes while leaves are still green.
• A distinct line of discoloration between healthy and diseased tissue if you look at a cross-section of a branch.

Why it matters:

Oak wilt is often fatal, especially to red oaks, which can die within weeks of showing symptoms. White oaks may decline more slowly but still require attention. Once a tree is infected, there are limited treatment options, so early diagnosis and preventative measures are critical.

Management strategies:

• Avoid pruning in summer and early fall. Fresh wounds attract beetles that spread the fungus.
• Remove infected trees promptly. Dead oaks should be cut down and properly disposed of to limit further spread.
• Consider fungicide treatments. For high-value oaks not yet showing symptoms, certified arborists can apply preventative fungicides that help protect trees in high-risk areas.
• Disrupt root grafts if necessary. In some cases, specialized trenching may be used to separate root systems and stop underground spread.

At Homer Tree Care, our ISA Certified Arborists are trained to recognize oak wilt and guide you through the best course of action for your property.

Fall Webworms: Unsightly but Manageable

What they are:

Fall webworms are caterpillars that spin large, messy webs at the ends of tree branches in late summer and fall. Unlike spring tent caterpillars, which start at tree trunks, webworms spread out along branch tips. They feed on leaves inside the protective webbing, leaving a tattered appearance behind.

What to watch for in fall:

• Silky webbing covering branch ends, sometimes spanning several feet.
• Clusters of small caterpillars feeding inside the web.
• Defoliation in localized sections of the tree canopy.

Why it matters:

The good news is that fall webworms rarely cause permanent damage to healthy, established trees. Most of the feeding happens late in the season, when trees are already preparing for dormancy. However, heavy infestations can weaken young or stressed trees, and the webs are unattractive in a well-kept landscape.

Management strategies:

• Prune out affected branches. Small webs can be removed with careful pruning or even cut out by hand.
• Encourage natural predators. Birds and beneficial insects feed on webworms, helping keep populations in check.
• Professional treatment. For large infestations or sensitive trees, arborists can apply targeted insecticidal sprays to suppress webworm populations.

Protecting Your Trees This Fall

As a homeowner, it’s important to recognize that not all fall tree issues are equal. Oak wilt is a deadly disease that requires swift professional action, while fall webworms are primarily a nuisance but can still stress your trees if left unchecked.

The best way to protect your landscape is with a professional tree health inspection. At Homer Tree Care, we provide detailed assessments, proper diagnosis, and tailored treatment plans to keep your trees safe and thriving year-round.

Call to Action

If you’ve noticed unusual leaf drop, canopy thinning, or webbing in your trees this September, don’t wait until the problem gets worse. Contact Homer Tree Care today to schedule a consultation with one of our certified arborists. We’ll help you identify the issue and take the right steps to keep your property looking its best this fall—and for many seasons to come.