The Importance of Recognizing Diseased Trees

By MNR News posted 04-29-2022 11:33

As a Realtor® you have a solid understanding of a home’s big-ticket items, from the furnace and plumbing to the roof and foundation.

But there’s another big-ticket item that sometimes gets overlooked: trees. Specifically, diseased trees. While we’re fortunate to live in a state that is home to beautiful trees such as oak, ash, birch, and maple, Realtors® and homeowners alike need to be aware of the threats that an unhealthy tree may pose.

Know the Risks

When a tree becomes diseased, it’s a hazard to the property. Diseased trees are more likely to drop branches than healthy ones, and if the tree covers any part of the home in question, the risk of damage to the roof or other parts of the structure increases. And of course, the larger the tree, the greater the risk—both to the inhabitants and the property itself.

What follows is a list of some of the most common tree diseases in Minnesota. While by no means comprehensive, Realtors® should at least be aware of these diseases to help clients make informed decisions when buying or selling real estate.

Oak Wilt

Every species of oak tree in Minnesota is susceptible to Oak Wilt. This disease, caused by an invasive fungus, will eventually kill the infected tree. Some of the tell-tale signs of a tree infected by oak wilt are:

  • Discoloration of leaves, around the edges in particular
  • Total drop of leaves by midsummer
  • Dying upper portions of the tree
  • The onset of “suckers”—branches growing from the tree’s base

Healthy oak trees are beautiful, and properties with them are sought after for good reason. But a diseased oak tree can be a major liability, so recognizing the infection will help you advise your clients accordingly.

Dutch Elm Disease

Another fungi-related infection is Dutch Elm disease (DED). It most commonly occurs in American elm, Red elm, and Rock elm trees. As with Oak Wilt, this disease causes an infected tree to die. However, if caught early, the affected areas can be pruned, and the tree can be saved. Signs of Dutch Elm disease include:

  • Out of season yellowing/browning of outer leaves, eventually spreading towards trunk
  • Late spring/early summer drop of leaves
  • Brown streaking underneath bark of infected branches

As noted above, some Elm trees can be treated with fungicides to prevent trees from DED-related death.

Emerald Ash Borer

Perhaps one of the most insidious pests, the Emerald Ash Borer (EAB) is an invasive insect that is hard to detect until it’s too late. If left unchecked, EABs will kill trees they infest. EABs are beetles that affect ash trees. Signs of EABs on a tree are difficult to spot, making this a tough one for any Realtor® or homeowner. Here are a few things that may indicate their presence:

  • Excessive woodpeckers on a tree
  • Spotting the actual beetle —which has a metallic green color—on a tree, (not always easy to do, but it’s possible)
  • Thinning and yellowing leaves
  • D-shaped holes in the bark

If you suspect a tree has been invaded by the Emerald Ash Borer, it’s advisable to call an arborist. They can assess the tree and provide expert analysis and recommendations.


Another common disease to trees native to Minnesota is anthracnose. This fungus can infect several species of Minnesota trees, but most commonly infects oak, ash, and maple trees. Signs of anthracnose include:

  • Curling/darkening edges of leaves
  • Early leaf drop

Here’s some good news: anthracnose does not result in the death of the tree. Therefore, the risk of a tree falling or causing other damage to a property is extremely low. Nonetheless, given how common anthracnose is, Realtors® and homeowners should be aware of this disease. Recommended treatment includes pruning diseased branches and raking up fallen, diseased leaves soon after dropping.

Apple Scab

The most common disease affecting apple and crabapple trees in Minnesota is apple scab. If you’ve been to an apple orchard in the fall, you’ve likely encountered trees infected with apple scab. Signs are usually easy to spot, and include:

  • Olive green spots visible on leaves
  • Apples that have black lesions and/or brown spots

In most cases, fungicides can treat a tree with apple scab. Proper timing of treatment is important, so it’s helpful to consult an arborist.

Stay Informed and Connected

As with any potential problems on a property, knowledge is power. Educating yourself on common things to look for concerning diseased trees will help you advise your clients. You could also consider partnering with a local arborist to seek expert advice when needed. When it comes to homeownership in Minnesota, buying and selling property with healthy trees will help you and your clients in the long run.