Common Tree Diseases in Wisconsin

Updated June 5th, 2023

Common Tree Diseases

We use a process called macro-infusion at the base of the tree to protect your trees from common tree diseases such as Oak Wilt, Dutch Elm’s disease, & Sycamore/Ash Anthranose. These treatments can deliver up to 3 years of protection. Timing of these treatments are critical. We apply fungicide treatments to trees with other common diseases such as apple scab, rhizosphaera, fire blight, cytospora canker, & others. Timing of these treatments is critical as well.

Insect Control

We perform soil applied, basal drenches & soil injections with systemic insecticides to treat insect problems such as Emerald Ash Borer (EAB), Bronze birch borer, ash plant bug, ash flower gall, gypsy moth, Japanese beetles, aphids, leafhoppers, caterpillars, mites, gall insects,& an array of other sucking insects, defoliators, & borers. Basal drenches can be done without any spraying or wounding of the tree. Timing is critical for applying insecticides.

NOTE: In regards to Emerald Ash Borer, preventatively treating your ash trees is the best defense.

Other Disorders

We use a process called macro-infusion at the base of the tree to treat trees w/ chlorosis (yellowing of the leaves from a mineral deficiency or from root system health). Results from this treatment can last up to 3 years. You will have a healthier, greener tree (you will definitely see the results). We perform soil applied, basal drenches to apply growth regulators to trees. Growth regulators are used to achieve the following:

(1) To slow the growth of a tree that is in a confined area,

(2) To slow the growth of a tree that is close to a building, driveway, or deck.

(3) They can also be used to help stabilize declining trees or trees with injured root systems by encouraging root growth. Other tree disorders could be caused from things such as girdling roots,herbicide drifting, & salt, animal, or winter damages.

About Tree Diseases

Nothing is more horrific to any gardener, hobbyist, or professional than seeing a beloved tree dying from disease. Trees can become infected with disease, just like people and animals, and there are many different bacterial and fungal infections from which the trees might suffer. Tree disease is caused by varying factors, including the tree’s geographical location, weather, soil conditions, and the overall health of the tree and other plant life surrounding it. Where a person lives and plants a tree, will dictate the tree diseases that one should worry about.

If caught in time, tree disease is not necessarily a death sentence. Many common tree diseases can be treated by the grower once the specific bacterial or fungal culprit is identified. In worst-case scenarios, professionals can be brought in to cure the tree or remove it completely, if it is too late to save the plant. Damage can also be avoided by knowing the common tree diseases prevalent in the geographic area and purchasing and planting trees resistant to the area’s problematic types. Diligently monitoring the tree’s fertilizer, light, soil, and watering conditions will also help keep disease at bay.

Here are some of the more common tree diseases…

Canker Disease

  • Canker tree disease comes in three common forms, Cytospora, Nectria, and Phomopsis, and resembles a blister on the tree’s bark or branch much like a canker sore.
  • Cytospora canker commonly infects pine, poplar, spruce, and willow trees; Nectria canker is known to infect honey locust, maple, and oak trees; Phomopsis canker might attack arborvitae, Douglas fir, juniper, and Russian olive trees.
  • Canker tree disease is caused by an open wound on the tree’s branches that has become infected with one of dozens of bacteria or fungus of numerous classifications.

Heart Rot Disease

  • Heart rot tree disease can infect many deciduous trees, such as beech, birch, cedar, dogwood, and maple trees, that are improperly pruned, left with broken branches, or damaged by fire, insects, or animals.
  • Much like canker disease, heart rot tree disease is also caused by several species of fungus, such as the Fistulina hepatica, that has grown on the tree’s open wound or bare wood.
  • Tree growers suspecting heart rot infection should look for conk or mushroom bodies growing on the tree, as these are true sign of the presence of fungus.

Powdery Mildew Disease

  • Catalpa, chokeberry, crabapple, and linden trees are most likely to suffer powdery mildew disease, although the mildew is known to attack nearly all vegetation in the right conditions.
  • Tree growers noticing a white or gray powdery growth resembling talcum powder on the leaves of their trees might have a powdery mildew problem.
  • Powdery mildew is most common in warm, dry climates, and the fungi responsible for powdery mildew are of the Erysiphale classification.

Root and Butt Rot Disease

  • Three forms of root and butt rot disease – Armillaria, Hypoxylon deustum, and black root rot – can infect hardwood trees at their roots and butt, which is the base of the tree’s trunk at ground level.
  • Armillaria attacks the roots and butts of weakened conifer and broad-leaved trees; Hypoxylon deustum attacks tree roots and butts through mechanical wounds on hardwood trees; black root rot decays the roots of stressed hardwoods.
  • Root and butt rot disease is a black, leathery fungus, such as the viral Serpula himantioides fungus, that spreads up the tree’s trunk from the ground; mushrooms might also be present growing in the soil at the base of the tree.

Sooty Mold Disease

  • Boxelder, elm, linden, and maples are most likely susceptible to sooty mold tree disease. However, this disease is known to attack several species of trees where a feeding insect population is prevalent.
  • The sooty mold fungus – which includes molds of the Antennariella, Aureobasidium, Capnodium, Cladosporium, Limacinula, and Scorias varieties feeds off the insect honeydew and is a black, powdery coating found on the tree’s leaves and surrounding soil.

Verticillium Wilt Disease

  • Verticillium alboatrum, or Verticillium wilt, is a soil-borne disease that is known to most commonly attack catalpa, elm, maple, and stone fruit trees.
  • The disease is particularly problematic because it infects the tree via its root system.  This causes the tree leaves to turn a lighter color, look somewhat disheveled, and eventually wilt and drop from the branches.
  • Verticillium wilt is a highly contagious tree disease. The fungus can spread quickly through the soil to other garden life.


As the owner of this award-winning tree service company, Chris Voss has a wealth of knowledge and extensive experience in the tree service industry dating back to 1999. Chris is an ISA Certified Arborist, ISA #WI-0567A, which certifies he has a professional level of knowledge and skill in the field of arboriculture. 

Chris is also licensed and certified for the application of pesticides including fungicides and insecticides by the State of Wisconsin Department of Agriculture, Trade and Consumer Protection.

Tree Diseases

Understanding Tree Diseases in Wisconsin

By understanding the common causes of tree diseases in Wisconsin and implementing preventive measures, you can protect your trees from potential harm and ensure their longevity. Our team of experts is ready to assist you with any tree-related concerns and provide professional advice tailored to your specific needs. 

Let’s delve into the main causes of tree diseases in Wisconsin and how you can prevent them. 

Leaves With Apple Scab, Germantown, Wi.

Fungal Infections

Fungal infections are one of the leading causes of tree diseases in Wisconsin. Moisture and warm temperatures create favorable conditions for fungi to thrive. Common fungal infections include anthracnose, powdery mildew, and root rot. These infections can weaken the tree’s immune system, making it more susceptible to other diseases and insect infestations.

Leaves With Fireblight, Ozaukee, Wi.

Bacterial Infections

Bacterial infections can also affect trees in Wisconsin. They often enter through wounds, such as pruning cuts or insect damage. Once inside the tree, bacteria multiply and cause various diseases, such as fire blight and bacterial leaf scorch. These infections can spread rapidly and have detrimental effects on the tree’s overall health.

Tree With Leaf Scorch, Elm Grove, Wi.

Environmental Stress

Trees that are subjected to environmental stress are more vulnerable to diseases. Harsh weather conditions, such as drought, excessive heat, or severe cold, weaken the tree’s defenses and make it more susceptible to infections. Additionally, poor soil conditions, improper planting techniques, and inadequate nutrition can also contribute to tree stress and disease development.

Elm Bark Beetles, Brookfield, Wi.

Disease Transmission

Insects play a significant role in spreading diseases among trees in Wisconsin. Certain insects act as carriers, transferring pathogens from infected trees to healthy ones. For example, the elm bark beetle is a notorious insect that spreads devastating tree diseases. It’s essential to monitor and control insect populations to prevent the transmission of diseases.

Common Tree Diseases in Wisconsin: Cause and Treatment

Elm With Flagging Leaves, Elm Grove, Wi. Common Milwaukee County Trees.

Dutch Elm Disease

Dutch Elm Disease is one of the most prevalent tree diseases in Wisconsin, affecting the majestic elm trees that add charm to the landscape. It is caused by a fungus that is spread by elm bark beetles. Infected trees often display symptoms such as yellowing and wilting leaves, as well as the development of brown streaks on the bark. 

Treatment: Early detection and prompt action are crucial in managing Dutch Elm Disease. Professional arborists can provide pruning and insect control measures to prevent the spread of the disease. In severe cases, tree removal might be necessary to prevent further contamination. 

Diseased Leaves That Require Tree Health Care, Ozaukee, Wi.

Oak Wilt

Oak Wilt is a devastating disease that primarily affects oak trees, including the iconic species found in Wisconsin. It is caused by a fungus that disrupts the water-conducting vessels within the tree, leading to wilted leaves and eventual tree death. The disease spreads through root grafts between adjacent oak trees or by sap-feeding beetles. 

Treatment: If diagnosed early, some trees infected with Oak Wilt can be treated with appropriate fungicide injections to control the disease’s progression. However, preventive measures such as trenching and removing infected trees are often necessary to safeguard nearby oaks from contamination. 

Leaves With Apple Scab, Germantown, Wi.

Apple Scab

Apple Scab is a common fungal disease that affects apple trees in Wisconsin. It causes dark, scaly lesions on the leaves, fruit, and even the tree’s twigs. Infected trees may experience defoliation, leading to reduced fruit quality and yield. 

Treatment: Regular inspection and maintenance practices are vital in managing Apple Scab. Fungicides, proper pruning, and removal of fallen leaves can help control the spread of the disease. Planting disease-resistant apple tree varieties can also be an effective preventive measure. 

Cedar Apple Rust, Germantown, Wi.

Cedar Apple Rust

Cedar Apple Rust is a fungal disease that has a complex life cycle involving both cedar or juniper trees and apple family trees like Crabapples and Hawthorns.

The disease causes unsightly deformities on the leaves, affecting the tree’s aesthetics and reduces its ability to photosynthesize. Infected trees tend to grow slower and weaker, and fruit may drop prematurely.  

Fungicide sprays applied during spring and summer create a protective barrier on the leaves and fruit, preventing the fungus from taking hold.

Chlorotic Leaves, Big Bend, Wi.

Chlorotic Leaves

Chlorotic leaf disease manifests as the yellowing of leaves due to a deficiency in essential nutrients, most notably iron. This disease can significantly damage the health and appearance of oak trees if left untreated. 

Deep root fertilization involves injecting essential nutrients, including iron, directly into the tree’s root zone, bypassing alkaline soil and ensuring optimal absorption.

Diplodia Tip Blight, Big Bend, Wi.

Diplodia Tip Blight

Diplodia Tip Blight primarily targets the new growth of Austrian Pine trees. This means it infects the shoots and the developing pine cones. It manifests as brown or tan needles at the tips of branches, giving the tree a “flagged” appearance and stunted growth. The fungus infiltrates and kills the young shoots and produces spores, which can spread to neighboring trees. 

Regular applications of specially formulated fungicides, especially during the spring when new growth is emerging, create a protective barrier against the fungus. Insecticides can help manage bark beetles or other insects that create entry points for the fungus.

Leaves With Fireblight, Ozaukee, Wi.

Fire Blight

Fire Blight is a highly contagious bacterial disease that affects several tree species, primarily crabapple and pear trees. The open blossoms in spring provide an entry point for the disease.

Fungicides create a protective barrier on tree surfaces, inhibiting bacterial growth. Insecticides can help deter insects like bees and flies can inadvertently carry Fire Blight bacteria from tree to tree.

Rhizosphaera Needlecast On A Spruce Tree, Muskego, Wi.

Rhizosphaera Needlecast

Rhizosphaera Needlecast is a common fungal disease that primarily targets the needles of Spruce trees, causing them to turn brown and eventually fall off. This can lead to a noticeable thinning of the tree canopy and a weakened overall appearance. It interferes with the normal photosynthesis process, turning the needles from a healthy green to a discolored brown or purple.

Applying fungicides preventatively and curatively can slow and stop the disease from spreading, allowing the tree to recover and produce healthy new growth.


Preventing Tree Diseases

Taking preventive measures is crucial to maintaining the health of your trees. By understanding the common causes of tree diseases in Wisconsin and implementing preventive measures, you can protect your trees from potential harm and ensure their longevity. Our team of experts is ready to assist you with any tree-related concerns and provide professional advice tailored to your specific needs. 

Here are some proactive steps you can take to prevent tree diseases:

Anlts Tree Diseases Pine Tree Gloves Magnifying Glass 600X450 Compressed

Regular Inspections:

Schedule regular inspections with a certified arborist to identify early signs of disease and address them promptly.


Professional Care:

Seek professional tree care services, including regular maintenance and disease prevention programs, to ensure the well-being of your trees.

A New Leaf Tree Service Tree Trimming After 1

Proper Trimming:

Ensure trees are pruned correctly to minimize wounds and create optimal airflow, reducing the risk of infections.

Man Performing Preventative Tree Care In Germantown, Wi.

Insect Control:

Proper pruning reduces the risk of infestations. Insects or other pests can serve as carriers of disease, leading to infection.


Promote Tree Health:

Ensure trees are trimmed correctly to minimize wounds and create optimal airflow, reducing the risk of infections.

By understanding the common causes of tree diseases in Wisconsin and implementing preventive measures, you can protect your trees from potential harm and ensure their longevity. Our team of experts is ready to assist you with any tree-related concerns and provide professional advice tailored to your specific needs. 

A New Leaf Tree Service