Tree Insects & Diseases

The Parks and Forestry Division are committed to the urban forest canopy and part of that commitment is managing insects and diseases to the best of our available resources. We are proactively monitoring our urban forest for insects and diseases and basing management decisions on past and present practices, research and available funding to ensure a healthier urban forest.

Emerald Ash Borer

City staff has found and confirmed with the Department of Agriculture, Trade and Consumer Protection (DATCP) and with the DNR that Emerald Ash Borer (EAB) is in Oconomowoc. The Emerald Ash Borer (EAB) is an exotic woodborer that was found attacking and killing ash trees in Michigan during 2002. Since its detection, EAB has killed millions of ash trees and is now found in Illinois, Indiana, Iowa, Kentucky, Maryland, Michigan, Minnesota, Missouri, New York, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, Wisconsin and Ontario and Quebec Canada. EAB is easily spread through the movement of firewood, logs and nursery stock. The City of Oconomowoc has an estimated 463 public ash trees (streets/parks/open space) that were located and cataloged during public tree inventories conducted in 2006 and 2011. We do not have an inventory of private trees in the community, but the impact will be significant. The community will see the impact of EAB of the next 10+ years.

The Parks and Forestry Division is proactively checking ash trees for this destructive insect and has an Emerald Ash Borer Readiness Plan in place to help us be more prepared when this insect arrives. Preventative measures such as not planting ash trees and not transporting firewood long distances can really help to contain this insect.

If you suspect that your ash tree has an infestation or you think you have found an insect, please refer to the following website for key information on what the insect looks like, who to call, etc. 

You can also fill out a form to have Oconomowoc Parks, Recreation & Forestry staff inspect a city street tree if you think it is infected. You can download the form here.

Don't delay in your decision to remove a tree. Even if you think a tree is healthy, it can become more costly to remove an infested tree that has been standing longer than removing a healthy looking tree and replacing it. Read more on this here.

Emerald Ash Borer Sightings should be reported by calling the EAB Reporting Line at 1-800-462-2803 or online. If you call in a report of EAB, make sure to identify yourself by name.”  

Japanese Beetles

Japanese beetles are destructive insects native to Japan and was first discovered in New Jersey in 1916. It has since spread to nearly every state East of the Mississippi River. Japanese beetles affect over 300 species of woody and herbaceous plants that include turf, trees and ornamentals making it one of the most damaging pests of urban landscapes. Japanese beetle has a one year life cycle, spending most of its time underground as a grub and is prevalent with heavy populations in the Oconomowoc area. Adults are active generally from June to August.
Japanese beetle traps are not effective and are not recommended for use unless special conditions can be met. The traps have been demonstrated to be effective in reducing damage and populations only when landscapes are isolated from other Japanese beetle breeding areas or when mass trapping, all home owners in the neighborhood, use them.
For more information on Japanese beetles: 

Gypsy Moth

Gypsy moth is a destructive insect that is native to Europe, Asia and North Africa. It was introduced in North America in 1889 and has been spreading West ever since its arrival. It reached Wisconsin in the late 1980s and their natural populations can explode to very high numbers. Outbreaks like this occur about every 10 years or so. Gypsy moths feed on about 500 different species of trees and shrubs. Many counties participate in an annual gypsy moth suppression program to keep potential defoliation to a minimum.
For more information on gypsy moth: 


Oak Wilt

Oak wilt is a fungal disease that affects the red and white oak group and it inhibits the tree’s ability to pass water throughout the canopy from the. Oak wilt is spread by sap feeding beetles that fly from fungal mats on infected oak trees to healthier oak trees to feed on sap flowing from fresh wounds. It is also transferred through interconnected oak roots and from moving firewood infected with oak wilt.
For more information on oak wilt: 

Dothistroma Needle Blight

Dothistroma needle blight is a fungus that causes needle spots, discoloration and needle loss in heavily infected areas to several species of pine trees. Dothistroma has been observed in the Oconomowoc area.
For more information on Dothistroma needle blight: 

Rhizosphaera Needle Cast

Rhizosphaera needle cast is a fungal disease that primarily deteriorates the appearance of pines and spruces, especially Colorado blue spruce. The disease is prevalent in Oconomowoc and one preventative measure would be to plant tree species other than Colorado blue spruce.
For more information on Rhizosphaera needle cast: 

Additional information

What Insect is This?    
This website has great information on insect identification for indoor or outdoor insects.

UW Department of Entomology Click Here
This website also has great information on insect identification for indoor or outdoor insects.

UW Plant Disease Diagnostic Clinic
This website provides assistance and education on plant diseases and how to submit samples for testing.

What’s Wrong With My Deciduous Plant?
What’s Wrong With My Coniferous Plant?