In 2021, the City  experienced an increase in spongy moth (formerly known as gypsy moth) populations in concentrated areas of the city. Spongy moth is an invasive pest that is capable of feeding on over 300 different species of trees and plants, however, their preferred species are oaks. While healthy trees can withstand and recover from mild defoliation, stressed trees are more likely to succumb to high levels of defoliation during these outbreak years.

Based on the severity of the outbreak in 2021, the City conducted an aerial spray of the core impacted area located in the Dee-Devon Forest Preserve area, commonly referred to as Southwest Woods in spring of 2022. While control of the pest was successful in the treatment area, the pest had naturally spread into adjacent residential properties resulting in defoliation of mature oak trees and nuisance caterpillars impacting the quality of life of our residents.  This triggered a winter egg mass survey which indicated a very high population of spongy moth present resulting in additional aerial treatments in spring of 2023.

February 2024 Update
Visual surveys were conducted in summer 2023 to determine effectiveness of the treatment and feeding pressure on trees in both treated and non-treated areas. These surveys indicated extremely effective caterpillar control and minimal leaf feeding pressure. Additional winter surveys indicated that spongy moth pressure was expected to remain low in 2024.  Effective treatments and the build up of natural disease is likely contributing to the declining spongy moth population which usually occurs within 1-3 years of an infestation's peak. 

While there still may be isolated concentrations of spongy moth present in the city, overall, there has been minimal feeding pressure on the city's trees and a noticeable decline in the abundance of caterpillars. Therefore, the City will not be conducting aerial treatments for spongy moth in 2024.  

What should I do about trees on my property?
Check out the Illinois Department of Agriculture's webpage for additional spongy moth information and homeowner recommendations. 

Keeping a tree healthy is the best defense against spongy moth caterpillars. Properly mulching and feeding trees along with making sure they receive enough water (1 inch per week when dry) will help keep your trees healthy and viable.

If you have experienced moderate to severe defoliation, treatment might be a good option. Many local tree care companies deliver safe and effective treatments for trees on private property. Tree-äge® is one product used by tree care professionals to control spongy moth and it is the same product we use to treat ash trees for emerald ash borer. The product is simply injected into the tree’s vascular system in the most effective and environmentally responsible way possible. As a preventative treatment, it can protect the entire canopy for up to two years so in many cases one treatment is all that is needed since spongy moth populations naturally decline within 1-3 years. 

Note: Injections are performed as a preventative treatment and should take place in early spring before caterpillar emergence. Once caterpillar feeding begins, treatments will not be effective.

For more information, please visit the follow resources:
Illinois Department of Agriculture (IDA) - Lymantria Dispar/Spongy Moth
Michigan State University Extension - Spongy Moth IPM
University of Wisconsin-Madison - Spongy Moth in Wisconsin
United States Department of Agriculture (USDA) - Gypsy Moth
United States Department of Agriculture (USDA) - Leaflet 162 - Spongy Moth
National Slow the Spread Program

Btk Information
Btk: One Management Option for Spongy Moth - Michigan State University 
Foray 48B - Valent BioSciences - Product Label
Foray 48B - Valent Biosciences - Safety Data Sheet

In recent years, there has been a noticeable decline of established and mature oak trees across Park Ridge and the Midwest. These oaks, estimated to be 100-200 years old, are a keystone species and the last remaining remnants of the oak-prairie that existed where Park Ridge now sits. While recent droughts, climate effects, and other environmental variables have contributed to oak decline, researchers continue trying to find more conclusive reasons for the problem.

In 2023, additional soil samples were taken near declining oaks in Park Ridge with all samples testing positive for water molds including Phytophthora. Common site characteristics between those in Park Ridge and others in northern Illinois included poorly drained clay soils, flat slopes, and low levels of calcium and phosphorous which help suppress phytopthora. While these fungi are contributing to oak decline, they are also found in soils near healthy trees making this problem more complex.

Multi-year studies are currently being conducted statewide by researchers from the Morton Arboretum.

Management
Unfortunately, oak decline is typically not reversible. Therefore, it is important to prevent oak decline by keeping your tree healthy. This includes supplemental watering during periods of drought, proper mulching, nutrient feeds (tree fertilizer), and soil modifications if compacted and clayey. Contact a local Certified Arborist for additional management options.

History
Dutch Elm Disease (DED) is the most destructive disease amongst shade trees in the United States and is caused by a fungus called Ceratocystis ulmi or also called Ophiostoma ulmi. It entered North America in the 1930s by elm logs from Europe, used to make veneer. And by the 1960’s, the disease made its way into Park Ridge. The devastating history of DED in Park Ridge was recorded by then-City Forester John Morrell and can be found in numerous memos and newspaper articles.

Earliest records indicate that in 1969, elm trees made up over 50% of Park Ridge’s parkway tree canopy with over 10,000 elms. In the following decades, nearly all the native elm population would succumb to the disease. Today, many of the massive elms that once formed a cathedral-like canopy over the streets of Park Ridge are gone. 460 American elms can still be found in the City’s parkways, many of which are being treated as these mature trees hold a value for our community that is worth preserving. Additionally, new American elm cultivars with high tolerance to DED are still being planted in the City in an effort to restore these majestic specimen trees.

How does DED spread?
The disease spreads mostly by native and non-native elm bark beetles. As parts of an elm tree dies, the beetle utilizes the dead area as breeding grounds. The female beetle will lay eggs under the bark of dead and dying elm trees, or logs. When the eggs hatch, larvae tunnel their way through infected wood and later emerge from the tree carrying spores of the fungus on their body. They then are attracted to the scent of healthy elms and/or dying elms, which in turn start the process over again.

DED Detection
The earliest detection of DED is wilting leaves in a portion of the tree. As the leaves wilt, the healthy green leaves turn a dull yellow, then finally brown. The leaves curl up, and drop prematurely. DED can kill a tree within weeks and up to several years. An easy detection method you can do while sampling for DED is to peel the outer bark from a branch where wilting and yellow leaves are observed. If it has DED, there will be brown stripes, in contrast to the clear yellow wood of healthy trees (see photo). This discoloration is an accurate indicator of DED. 

Prevention & Treatment
While there are no cures for DED, treatment options, such as Arbotect injections, are available as a preventative measure. Additionally, chemical insecticides can be used to control the elm bark beetle. Contact a local certified arborist for more information about treatment options.

It is recommended that elm trees only be pruned during the dormant season, November 15 – March 15. These dates may fluctuate due to unseasonal temperatures.

Additional Information
Dutch Elm Disease - USDA National Invasive Species Information Center

There are many common leaf diseases that can have striking visual affects on trees. Fortunately, most common leaf diseases do not cause significant harm to tree health. Knowing the signs of these common ailments can help you identify small nuisances or alert you to more severe issues that may need to be addressed. A local Certified Arborist or tree care company can help diagnose these issues and recommend any treatment options if necessary. 

The City does not treat parkway trees for common leaf diseases.

Anthracnose is a fungal disease that commonly affects the leaves of many species of shade trees. Anthracnose is characterized by tan or brown spots on the leaves of the lower and inner branches of an infected tree. Leaves may also appear cupped, curled, or generally distorted in nature. In severe cases, infected leaves can drop prematurely. After dropping infected leaves, trees will produce a second set of leaves by midsummer.

Anthracnose is most common in years with prolonged cool, wet weather in the spring. Anthracnose infections can persist and spread as long as these weather conditions remain. As the weather warms and dries throughout the summer, disease spread ends and affected trees will replace any lost leaves.

 Anthracnose infected oak leaves (extension.umn.edu).

Tar Spot of Maples
Tar spot is a fungal disease that commonly affects the leaves of maple trees. Tar spot begins to appear in early spring, manifesting as light green or yellow spots on leaves. As the summer progresses, spots will darken in color until they are dark brown or black. There are multiple pathogens that cause tar spot in maples, and the size of the spots may vary. In some cases, spots may remain relatively small (often referred to as “specked tar spot”) and in others spots may grow up to an inch in diameter.

Tar spot infected maple leaves (ag.umass.edu)

Other Leaf Spot Diseases

There are numerous other leaf spot diseases that can be found in the landscape, many of which do not cause serious harm to tree health. Other leaf spot diseases can present in various forms, including large or small spots, blotches, or blisters, and in colors including yellow, green, red, orange, brown, or black. If you believe your tree has a leaf spot disease, raking and disposing of infected leaves before the first snow can help prevent infections in future seasons. Fungicides, although effective at controlling some leaf diseases, are typically not warranted. 

• Apple and crabapple (apple scab, rust, fire blight)
• Horsechestnut (leaf blotch)
• Serviceberry (rust, fire blight)
• Hawthorn (rust, fire blight)
• Pear (rust, fire blight) 
• Maple (tar spot, anthracnose)
• Sycamore (anthracnose)
• Oak (anthracnose, bacterial leaf scorch, blister)
• Linden (leaf blotch, anthracnose)

Additional information on other leaf spots and disease can be found here.

Similar to leaf spots and disease, there are many common pests that can leave tree leaves looking unsightly, tattered, or like swiss cheese. Fortunately, most common pests do not cause significant harm to tree health. Knowing the signs of these common pests can help you identify small nuisances or alert you to more severe issues that may need to be addressed. A local Certified Arborist or tree care company can help diagnose these issues and recommend any treatment options if necessary. 

The City does not treat parkway trees for common tree pests.

While there are pesticides available to deter elm flea weevil populations from feeding, treatment for this cosmetic issue is unnecessary.

Elm flea weevil damage (extension.umn.edu).

Leaf Galls
Plant galls are abnormal growths that can occur on many parts of a tree; most visibly on leaves and twigs. Most galls are caused by feeding or egg-laying activity by insects, commonly aphids, mites, wasps, or midges. Irritation caused by the insects stimulates production of both larger and faster growing cells, leading to the abnormal growths we know as galls. If galls begin to form, they will continue to grow, even after the insect that caused them dies.

The appearance of galls can vary from small bumps on leaf blades, to swollen areas or knots on twigs. While galls can be unsightly, they rarely are numerous enough to cause harm to trees. If galls are localized to one area of a tree, the affected limb or branch may be removed, but this is generally unnecessary as galls rarely cause permanent injury to a tree. Once galls have formed, treatment is ineffective as the insects are already protected within the gall itself.

Jumping Oak Gall on oak leaves (extension.umn.edu)

Maple spindle gall on sugar maple (canr.msu.edu)

Linden gall mite on linden (Zubrik, Forest Research Inst, bugwood.org)