Disease & Pest Management
Disease & Pest Management Overview
The City of Saint Paul remains committed in its efforts to manage tree losses to pests diseases such as emerald ash borer, bur oak blight, Dutch elm disease, oak wilt, and Nectria canker. Learn about the identification, treatment, and management of these diseases below.
Emerald Ash Borer
The emerald ash borer (EAB) is a non-native insect of major concern that was discovered in the Saint Anthony neighborhood of Saint Paul in 2009 and the Parks department immediately implemented a plan to address the issue. Forestry is collaborating with local, state and federal agencies on efforts to mitigate the effects of this destructive pest.
What's Happening with EAB in Saint Paul?
- Structured Removal of EAB infested ash trees:
- The EAB Management Plan calls for the removal, stump grinding, and replacement of public ash trees throughout the city. Most of the ash trees are removed via the Structured Removal portion of the EAB Management Plan.
- Structured Removal has been done annually since 2010.
- These removals generally take place early in the year (January - April), with stump grinding and replacement following immediately after.
- 2017, in comparison to previous years, has presented a new challenge as the total number of infested trees is growing at a more rapid rate. Therefore, the primary focus right now is removing trees before they pose a public safety threat.
- How this changes plans for 2017:
- Stump grinding and replanting will take place, but not immediately following removals as has been the case in previous years.
- Residents will be notified when a timeline for stump removal and replacement tree installation has been determined.
- New EAB FAQ - click on the link to read answers to our most commonly asked questions.
- Updated Homeowner's Guide to EAB - deciding what to do with your private ash tree(s) is a tough decision. Check out this page for help in your decision making.
- The green flagging on ash trees is an outreach effort to create awareness of the large number of ash trees throughout the City. All of these trees are threatened by EAB. The ribbons do not indicate that the tree is scheduled for removal, but since it is susceptible to EAB, it will eventually need to be removed.
Common EAB Questions
- How is the City of Saint Paul managing EAB?
- Where are known emerald ash borer infestations in Saint Paul and Minnesota?
- View the state-wide EAB infestation details from the Minnesota Department of Agriculture.
- How can I help slow the spread of EAB?
EAB Resources and Links
Bur Oak Blight
Bur oak blight (BOB) is a native plant disease caused by the fungus Tubakia iowensis. First identified in Iowa, BOB is a leaf disease that is beginning to affect more bur oaks in Saint Paul. More frequent precipitation over the last few years has increased the severity of the fungus which causes purple-brown lesions on the leaves.
Symptoms of this disease include late season leaf death starting in the bottom of the crown and moving upwards. If a tree is seriously infected one year, it tends to be severely infected the next year. Bur oaks infected with BOB generally decline and may die after several years as secondary pests such as two-lined chestnut borer invade the stressed trees. The combination of BOB and other stressors will eventually overwhelm the tree and cause mortality.
Compared to oak wilt in red oak trees, BOB does not spread rapidly. Healthy trees can be found adjacent to BOB-infected trees. Fungicides injections to control the fungus have shown to be effective when applied in low doses in the spring.
At this time, Forestry is not performing fungicide treatments on bur oaks infected with BOB. Forestry staff will continue to monitor the disease and assess trees with BOB.
Dutch Elm Disease
Dutch elm disease (DED) has killed hundreds of thousands of elms in Saint Paul since the late 1960s. Most of these elms were large trees lining the boulevards that created a tunnel-like effect down city streets. Management of the disease has allowed some of these iconic elm trees to remain scattered throughout the city. Continued management of this disease is necessary to mitigate the effects of this disease. Information on the DED lifecycle, vectors, signs, symptoms, and damage can be found here.
Public Property Management
Forestry uses a sanitation approach, which is the prompt removal of infested elm trees, to prevent the spread of DED. Forestry locates diseased elm trees as soon as possible so that they can be removed before further spread occurs. Tree inspectors licensed by the Minnesota Department of Natural Resources perform a tree survey of Saint Paul every summer to locate and mark diseased elm trees for removal. Inspectors use identification characteristics of the DED to determine whether or not an elm tree is diseased. In questionable situations, a sample may be taken and brought to the University of Minnesota's Plant Health Disease Clinic to determine whether or not the tree is diseased.
Private Property Management
City ordinance gives Forestry staff the right to actively pursue, identify, and require the removal of diseased elm trees and wood piles within Saint Paul on private property. Tree inspectors licensed by the Minnesota Department of Natural Resources locate and mark diseased elm trees and wood piles on private property for removal.
- Forestry will mark infested elm trees or wood piles with a painted red ring.
- An orange slip is left at the residence that informs the property owner of the diseased elm tree or wood pile and states that an official letter with removal specifications will be arriving in the mail.
- Once the letter is sent, the property owner will have 20 business days to remove the diseased elm tree or elm wood and properly dispose of the diseased wood including debarking the stump to ground level.
- If the work is not done in the time allotted, Forestry will have a hired contractor remove the tree and assess related costs to the property owner.
Fungicidal Treatment of Elms
Forestry does not use fungicidal treatments to help prevent DED in public elm trees. However, property owners may work with a licensed tree care company and apply for a free permit if they wish to treat boulevard elm trees.
Forestry also encourages property owners to treat their highly valued private property elms. A permit is not required when treating privately owned elm trees. However, Forestry recommends that property owners use a company with an ISA Certified Arborist® on staff.
- Dutch Elm Disease Identification, Biology, Management, and more
- Dutch Elm Disease Resistant Elm Trees
- Minnesota Department of Agriculture
Oak wilt is a fungal infection (Ceratocystis fagacearum), which causes oak mortality primarily in the red oak family. Oak wilt is spread by many species of sap beetles, but is most often transmitted via root grafting.
Public Property Management
Forestry only prunes oak trees in the winter in order to help prevent the spread of this disease.
Private Property Management
Tree inspectors identify and mark diseased oaks during the late summer or early fall. On private property, property owners have until the end of the calendar year to remove diseased trees.
Management of oak wilt is primarily focused in the Highwood/Battle Creek area where there are higher concentrations of red oaks and the disease is more prevalent. Forestry staff are available to advise property owners how to best manage and contain oak wilt. Forestry recommends that private property owners not prune oaks between April and October in order to help prevent infection from this fungus.
Nectria canker is a fungal infection which can cause tree mortality, especially in honey locusts. Forestry manages this disease by pruning honey locusts during winter, as the disease is dormant during this time and the chance of infection is greatly reduced. Pruning honey locust during winter has proven to be an effective management strategy for this disease.