Wisconsin is home to a range of native coniferous and deciduous trees that provide many benefits to your property. Well placed trees can reduce your cooling costs in summer by providing shade, act as a windbreak against bitter winter winds, decrease stormwater runoff to minimize erosion, and add aesthetic appeal to your landscape that can increase your property value. With all these benefits, keeping your trees healthy is important. Early detection and treatment of tree fungal diseases are crucial to protect your trees.

Wachtel Tree Science has put together this simple guide to help you identify common types of fungus on trees in Wisconsin and the signs of an infected tree. This guide also contains preventive measures you can take to protect trees against these issues along with treatment options to help affected trees. While this guide is a helpful resource, it is important to have your tree diagnosed by a Certified Arborist if you suspect your tree is affected. At Wachtel Tree Science, we have over 8 decades of experience in practicing the art of science-based tree care, and can start a custom health care plan for your trees.

How to Identify the Common Types of Tree Fungal Disease Found in Wisconsin

In the Midwest, there are a variety of tree fungi that can be dangerous to your trees. Various types of fungi impact different parts of a tree. Some will only impact the leaves, others can be much more severe causing a sudden decline in health or impact the structural integrity of a tree. Learn how to identify some common types of fungus on trees below.

Oak Wilt Disease

Oak wilt disease is a fatal fungal infection of oak trees that is widespread in southern Wisconsin according to the Wisconsin Department of Natural Resources. The fungus grows through the tree’s water conducting system. This, in turn, causes the tree’s defenses to respond eventually causing the water movement to be blocked within the tree which leads to wilted leaves and tree mortality.

Causes:

• Sap-feeding beetles carry oak wilt spores to fresh wounds, spreading the disease
• Interconnected root systems transmit the disease into nearby infected oak trees

Signs:

• Dull green/bronze leaves
• Rapid loss of leaves (often mid-summer)

Prevention:

• Avoid pruning or cutting oak trees at least from April through July (better to avoid cutting from April through September)
• Keep firewood local

Treatment:

• Trunk injection of systemic fungicide every two years (preventatively)
• Root graft trenching

Apple Scab

Apple scab is a fungal disease that infects leaves of ornamental crabapple trees, apple trees, and trees in the rose family. While the disease is not fatal, repeated infections and leaf loss can reduce a tree’s overall health and cause stress. Increased stress can leave it more susceptible to other diseases and insect infestations.

Causes:

• Transported by wind and rain
• Rainy, wet springs and summers

Signs:

• Small brown to olive green spots on leaves
• Early leaf drop

Prevention:

• Plant more resistant varieties such as Royal Raindrops, ‘Tina’ and ‘Red Jewel’
• Clean up infected leaves
• Prune tree for better air circulation through the canopy

Treatment:

• Fungicide treatment 2-3 times per year

Needlecast

Similar to needle blight, needle cast is a fungal disease that primarily infects pine and spruce trees that are common in southeastern Wisconsin. There are several species of needlecast fungi which cause inner needles to prematurely fall off, which results in your tree looking thin or sick. If your evergreens are looking a little “off”, your tree may have needle cast disease.

Causes:

• Rains or heavy dews
• Spread from infected needles by wind

Signs:

• Slow or rapid development of inner needle browning
• Loss of innermost needles on lower branches

Prevention:

• Avoid planting Colorado blue spruce as they are more susceptible
• Allow adequate spacing between trees when planting
• Remove and destroy diseased branches and needles

Treatment:

• Protective fungicide spray program
• Improving soil conditions and tree health

Dutch Elm Disease

A lethal fungal disease that infects elm trees is Dutch elm disease. The disease has led to the loss of the American elm as a primary street tree.

Causes:

• Elm bark beetles which transmit the fungal disease to elm trees
• Root grafts from adjacent infected elm trees

Signs:

• Symptoms typically arise in late spring or early summer
• Curling/wilting leaves on outer branches that turn gray-green or yellow, then brown and rapidly fall off

Prevention:

• Destroy infected parts of a tree including branches
• Preventative trunk injections
• Avoid pruning susceptible elms during the growing season

Treatment:

• Trunk injection
• Trenching to break root grafts

Anthracnose

Anthracnose is a common disease caused by several different kinds of fungi that affect foliage of trees found in Wisconsin. Species commonly at risk include maple, ash, oak, sycamore and walnut. It is generally a cosmetic disease that affects a tree’s appearance.

Causes:

• Reinfection from fungi lingering in leaf litter (host tree specific)
• Cool and moist conditions in the early growing season

Signs:

• Tan or brown spots on leaves
• Curling or premature drop of leaves
• Twig dieback in some tree species

Prevention:

• Removing and disposing fallen, infected leaves in fall
• Water and fertilize trees to maintain good vigor

Tar Spot

A cosmetic fungal leaf spot disease is tar spot. This disease is visually distinctive and can affect tree species such as maple, boxelder, and willow trees.

Causes:

• Tar spot fungi reinfection from leaf litter
• Spreads from tree to tree
• Spores commonly produced in spring

Signs:

• Early in the growing season, these will appear as yellowish spots on infected leaves
• As these infections mature the spots blacken, resembling blobs of tar

Prevention:

• Collect and dispose of fallen leaves in fall
• Fungicides can be utilized to deter tar spot

Science-Based Treatment of Tree Fungus Disease

To protect your trees from fungal diseases, early detection and intervention is crucial. Now that you know some signs to look for, the next step is to have your tree diagnosed by a local Certified Arborist if you suspect your tree is affected.

At Wachtel Tree Science, science is in our name! Our Certified Arborists have extensive experience managing tree disease and fungal issues. Whether your tree calls for trunk injections, soil treatments, or something else, we can prescribe a treatment plan to keep your trees healthy and beautiful!

Contact us today to assist your tree’s recovery.

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The crew conversed with us about exactly what they were going to do. We are very pleased with your team.

Susan – Wauwatosa, WI

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