common tree diseases in wisconsin

5 of the Most Common Tree Diseases of Wisconsin

Whether it’s a fruit tree or a conifer, your trees are a crucial part of your back yard’s ecoscape. They provide shade, comfort, and aesthetic appeal. But, when things go wrong, common disease can wreak havoc on your trees. 

You need to implement proper tree care if you want to keep your landscape healthy and hardy for years to come.  Learn about some of the main plant diseases to look out for in Wisconsin and surrounding areas. 

What Types of Tree Disease Should You Worry About In Wisconsin? 

Here in the midwest, there are different types of tree and shrub diseases that can infect plants. These conditions fall into various categories: 

  • Evergreen Diseases – infect evergreen trees like spruce, pine, and most other conifers. 
  • Deciduous Diseases – infect deciduous trees such as maple, ash, or fruit trees. 
  • Leaf Diseases – infect the leaves of a tree. 
  • Stem Diseases – target the trunk, branches, or “stem” of a plant or tree. 
  • Vascular Diseases – affect the entire vascular system of a tree. 
  • Fungal Diseases – caused by a fungal infection, generally brought on by too much moisture. 
  • Bacterial Diseases – caused by the overgrowth of harmful bacteria. 
  • Infestation – caused by an infestation of insects or other destructive parasites. 

You need to watch for all types of infections when caring for trees in your yard. Here are some of the most common plant diseases that can infect your trees. Check them out! 

1. Verticillium Wilt

Verticillium Wilt is a tree disease that will start by turning a plant's leaves brown.
[Image source: Wisconsin Horticulture]

Deciduous ornamental trees are particularly prone to Verticillium Wilt. This is a vascular disease that has no cure. It will eventually kill any infected plant. If you have maples or ash trees in your yard you need to pay especially close attention to them. These are the most commonly infected species.  

The first identifier of a Verticillium Wilt infection is leaf spots. Next, you will see yellowing, wilting, and dying of tree and shrub leaves and branches. Upon closer inspection, you will find internal streaking in the sapwood of branches.  

Yellowing inside the twig caused by the plant disease Verticilium Wilt.
[Image source: Wisconsin Horticulture]

While there is not a cure, you can prevent this type of infection with your species selection. Plant resistant trees like apple, sycamore, walnut, and willow. To extend the life of an infected tree, proper water and fertilization are crucial.  

2. Dutch Elm Disease

Dutch Elm Disease destroying the bark of a tree.
[Image source: Forestry News]

Spread by elm bark beetles, Dutch Elm Disease is a deadly fungal disease that can spread to other trees. This disease particularly affects Elm trees. In fact, it has led to the decline of this species as decorative street trees in most of the United States. The fungi responsible are Ophiostoma ulmi and Ophiostoma novo-ulmi.

The first indicator of Dutch Elm Disease is the sudden wilting or yellowing of leaves. An infection can be isolated to a single branch for many years before spreading to the rest of the tree. You can tell if elm bark beetles have been in your tree by lifting the bark. If you notice a creative display of artistic trails, you can be sure they have. An indicator of infection is dark brown streaks that follow the wood grain. 

To prevent Dutch Elm Disease, you must keep pruning tools clean when moving from elm tree to elm tree. Infected trees should be completely removed from the area. This will prevent its spread by bark beetles.

3. Fire Blight

Fire blight is a bacterial infection affecting trees and shrubs.
[Image source: Good Fruit Grower]

The most harmful bacterial infection affecting plants in the rose family, Fire Blight can kill or disfigure trees and shrubs. It is caused by an overgrowth of Erwinia amylovora. The following plants’ blossoms, leaves, and branches can be most susceptible. 

  • Rose
  • Apple
  • Crabapple
  • Pear
  • Hawthorn
  • Quince
  • Mountain Ash
  • Cotoneaster
  • Pyracantha
  • Spirea

In addition to the susceptibility of the species, the weather has an impact on the intensity and rate of spread of a Fire Blight infection. 

You can identify fire blight by the scorched or burnt look of clusters of leaves that do not drop from the plant. Infected plants look as though they have been burnt by fire. Eventually, “cankers” with a bacterial ooze can develop on the branches of the tree. 

While Fire Blight cannot be cured, pruning affected branches from the tree can help contain the spread of the infection. It is best to prune during dormant winter months. Be sure to disinfect your pruning tools in a bleach or alcohol solution with each cut to prevent further spread of this common plant disease. 

4. Rhizosphaera Needle Cast

Rhizosphaera Needle Cast
[Image source: Wisconsin Horticulture]

A fungal evergreen disease, Rhizosphaera Needle Cast can cause unsightly damage. It primarily affects spruce, fir, pine and hemlock species. Most commonly, this fungus affects Colorado Blue spruce and is caused by one of several bacteria in the Rhizosphaera family. 

You can identify this type of Needle Cast by looking at the base of the tree. If you notice discoloration, browning, and death of needles on the lower branches of a tree, this is probably what you’re seeing. Get a magnifying glass and check the needles you believe to be infected for small, black, spherical growths. If you find them, you’re certainly looking at Needle Cast. 

University of Massachusetts
[Image source: University of Massachusetts

Fungicides can help maintain and cure this disease. Look for copper or chlorothalonil as the active ingredient. This way, you will be sure the mixture is effective at eliminating Rhizosphaera. Cover all needles when spraying and reapply every several weeks. 

5. Oak Wilt

Oak leaves impacts by Oak Wilt, a tree disease cause by a fungus.
[Image source: Michigan State University]

Oak Wilt is a vascular disease caused by the fungal invader Bretziella fagacearum and infects both red and white oaks. The disease is contagious and spreads quickly by insects who carry the fungus from one oak to another. 

The first sign of Oak Wilt is usually a slight bronzing or discoloration of oak leaves. Soon, single branches will begin to fall off. Eventually, the diseased tree will die as there is no cure. 

One of the best ways to prevent the spread of Oak Wilt is to keep pruning tools clean between uses. And, to eliminate an infection, it is best to remove infected trees. Always burn stumps and roots after falling a tree. If you decide to keep the wood, keep it stored well away from other susceptible trees. 

Final Thoughts

These aren’t the only tree diseases to watch for, but they are the most common. If you suspect your trees are infected with a harmful illness, it is a good idea to ask an expert for a solid diagnosis before you try remedies at home. If you need help with your trees, contact us today! We would love to help.