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Trees: Insects and Diseases


Table 1: Contact information.
Contact Telephone
Public Works Department (630) 434-5460
Kerstin von der Heide, Village Forester (630) 434-5475

The Public Works Forestry Division continually monitors the parkway trees throughout the year looking for problems that may seriously impact tree health or threaten public safety. Residents are encouraged to report any unusual insects near parkway trees or declines in tree health.

Emerald Ash Borer Beetle (EAB)

Emerald Ash Borer is a serious pest which has caused the death of millions of native North American ash trees. Since it was first discovered in Michigan in 2002, the beetle has quickly spread across several states. Infestations have been found in all communities adjacent to Downers Grove, including Darien, Lombard, Westmont, Woodridge and Naperville.

Village ash trees are being inspected and monitored for this beetle pest. Along Village streets, ash trees make up 6% of the total parkway tree population, with some blocks consisting of all ash trees. In addition, declining and unhealthy ash trees are being removed to reduce potential breeding areas for the beetle.


Forestry staff is carefully scrutinizing all the ash trees in the Village inventory and is looking for any of eight identifiable signs and symptoms that an ash tree may be infested with EAB:

  • Dieback
  • Sprouting
  • Bark splits
  • D-shaped holes
  • S-shaped larvae galleries
  • Presence of larvae
  • Woodpecker damage
  • Presence of adult EAB beetles

If two or more signs and symptoms are present or the ash tree is at least 50% dead, trees will be removed.

Treatment of Village Ash Trees

In 2022, the Village will treat approximately 800 parkway ash trees.

There are also a number of ash trees that have been marked for removal with red spray paint markings on the trunk. Affected residents have been notified.

  • Interactive Forestry Map (select Village Trees)
    This map allows residents to view the species and size (diameter) of village parkway trees.

Related Links

Gypsy Moth

The Gypsy Moth is a serious pest that has been gradually spreading westward into Illinois. Since it was first accidentally introduced in Massachusetts in 1869, the Map of Gypsy Moth in US illustrates how far the insect has spread and extended its range. Forest and shade trees are vulnerable to this defoliating pest. In the last decade, Gypsy Moth has become a permanent resident of northeastern Illinois and parts of Downers Grove.

The Gypsy Moth and Control Measures document describes the insect and treatment plans by the Village in order to suppress their numbers. The Gypsy Moth Aerial Spray map outlines the locations in the Village which were sprayed in May 2009. The 2009 spraying was so effective that no further spraying has been necessary to date. Staff will continue to monitor for gypsy moth caterpillars throughout the Village using Burlap bands and reported sightings.

Over the past few years, parts of northeastern Illinois have sustained such large increases in Gypsy Moths numbers that eradication is no longer an option for state and federal Gypsy Moth spread programs. Because of this, Lake County was quarantined for Gypsy Moth in 2000. In 2007, McHenry, Cook and DuPage Counties were added to the quarantine area. A quarantine requires all nursery stock and firewood being shipped out of the regulated counties to be inspected and certified to be free of gypsy moth. All nurseries and nursery dealers are also required to treat their property and/or stock, and persons leaving quarantined counties have to have all of their outdoor equipment inspected. More information about the quarantine can be found at the Illinois Department of Agriculture Gypsy Moth website.

Though Downers Grove is now included in the quarantine area, residents can take several steps to protect their trees and reduce Gypsy Moth numbers. The easiest method involves putting up Burlap bands on tree trunks and collecting caterpillars every couple of days. Destroying Gypsy Moth egg masses by scraping them off surfaces or spraying them with a soybean oil product is also effective. Insecticides are also an option and should be applied by tree professionals to limit adverse environmental impacts.

More information about Gypsy Moth can be found at the USDA Forest Service Gypsy Moth website.

Honeylocust Tree Insects

Honeylocust Tree Insects were very numerous in 2009, but have been present in moderate numbers ever since. Because honeylocust trees represent more than 12% of the parkway tree population, insect feeding activities that cause foliar damage to honeylocust are noticeable throughout the Village. The Downers Grove Parkway Honeylocust Trees map shows the distribution of honeylocust trees with each olive green dot representing a honeylocust tree. There are several streets blocks colored almost a solid olive green due to the high numbers of honeylocust trees which were planted there.

Dutch Elm Disease

Dutch Elm Disease is a fungal disease which has been devastating elm trees in Downers Grove since the 1950’s. Once numbering in the thousands, American elms on Village parkways now number less than 360.

Fungus Growths

Fungus Growths on trees can indicate the presence of advanced tree and wood decay. Though the rest of the tree may appear normal and healthy with green foliage, fungus growths indicate the tree has lost structural strength and that it may break apart at the point where the growth is present. When sigificant growths are discovered on parkway trees, the trees are removed for public safety.

Additional Information on Pests and Diseases

The Morton Arboretum's Plant Clinic  helps homeowners, gardeners and landscape professionals throughout the Chicago region.