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Pests & Diseases
Pest and Disease Prevention
Wauwatosa's Forestry Section is committed to maintaining a healthy urban forest by following all cost-effective means to minimize diseases and pest infestations.

Dutch Elm Disease
Dutch elm disease (DED) is a fatal fungal disease that attacks American elms and is spread by Elm Bark beetles, which feed on healthy trees. One treatment that can help stop the spread of DED by elm bark beetles is the use of fungicides, which can be injected into the elm tree any time after leaves reach their full size. This treatment should be performed every year. The fungicide injection is not guaranteed effective, due to conditions within the tree and the environment, but it is one of the few viable options available. 

We presently use the fungicide Arbotect 20-S to help reduce the risk of infection to healthy trees from elm bark beetles. At the homeowner's request, we will inject your city elm tree (sorry, yard trees are not included) if it can be done safely and without excessive harm to the tree. We ask the resident to pay the cost of the chemical while we will provide labor and equipment. The chemical cost generally runs between $30 and $55 per tree. 

If you have a city elm tree, we will automatically send you a postcard in early spring reminding you to call us if you are interested in receiving the treatment. 

Emerald Ash Borer
Emerald Ash Borer (EAB) is a newly introduced insect that attacks and kills all species of ash trees. First discovered in Detroit in 2002, EAB has caused severe damage to ash populations in Michigan, Ohio, Illinois, Indiana, and the U.P. Four infestations are currently identified in Wisconsin, including one in southern Milwaukee County. It is a near certainty that Wauwatosa will have to deal with this pest in the near future. The Forestry section is kept abreast of the latest developments with EAB through weekly electronic newsletters from the Department of Agriculture, Trade and Consumer Protection,  (DATCP),  Department of Natural Resources (DNR), and the US Animal and Plant Health Inspection Service (APHIS). Our plan to combat this insect is to remove infested trees as quickly as possible to minimize the impact on neighboring trees. We are also exploring all cost effective methods of chemical control.

Gypsy Moth
This defoliating caterpillar has permanently established itself in our area. Populations fluctuate from year to year with corresponding fluctuation in leaf damage. Most trees can withstand a year or two of significant defoliation without permanent damage, however, beyond that the tree’s energy reserves can be depleted beyond its ability to recover. When gypsy moth populations have reached this damaging level, Wauwatosa has participated in the DNR’s aerial spray suppression programdesigned to drastically reduce the population by use of a chemical called BTK. The chemical is specific to caterpillars. Spray areas are determined by egg mass counts taken in the fall. Spraying takes place in early to mid-May. All residents in prospective spray areas are contacted by mail and given opportunities to attend public hearings well in advance of spraying. Report gypsy moth activity or egg masses to the Forestry Section.

You are strongly urged to sign up for the DNR’s Gypsy Moth Spray Notification Service by email. Once you are signed up, you will receive emails prior to spray activities in your area and when spray activity is completed, or cancelled for that day because of weather. You can subscribe from the Wisconsin Gypsy Moth webpage at In the “Who To Contact” box below two state maps on that page, click on the link Gypsy Moth Spray Email Signup. You will be directed to the Gypsy Moth Spray Email Signup page. (This page is at Read the directions and click the link to subscribe. 

If you do not have an email address or immediate access to an internet connection, you can find out about gypsy moth spray activities by calling the Wisconsin Cooperative Gypsy Moth Information Line at 1-800-642-6684 or 1-800-642-MOTH. The line is available 24 hours a day, 7 days a week and is updated frequently. You will need to call each day until the area you are interested in has been sprayed. 

Other sources of information include: 

Other Common Problems
There are many other diseases and pests that cause minor to insignificant damage to trees. If you discover something unusual on your city tree feel free to contact the Forestry Section. If we can’t diagnose it over the phone, someone will come out to inspect the tree. 

If you have a problem with your private tree, the UW Extension website may offer some help.

For information on Invasive Species, you can also visit the University of Wisconsin Weed Science page.

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