Tree illness is a condition of a tree’s health that is caused by biotic (fungi, bacteria, and pests) or abiotic (nutrient deficiency, environmental stresses) factors. Early detection of a tree disease is important for the homeowner, as many are communicable and can spread throughout a landscape if not addressed by a professional arborist such as Monkeyman’s Tree Service.
What are the most common tree diseases in the Pacific Northwest?
The Pacific Northwest (PNW) presents a unique environment for tree illness due to its high moisture levels and temperate winters, which create an ideal breeding ground for fungal and bacterial pathogens. Monkeyman’s Tree Service frequently encounters a specific set of diseases that target our native and ornamental species.
10 Common PNW Tree Diseases: Identification and Treatment
To protect your landscape, it is essential to recognize the specific pathogens common to our region. Here are the ten most frequent illnesses we diagnose:
1. Anthracnose (Fungal):
Symptoms: The “dead” spots are irregularly shaped and brown or black, and are grouped along the veins of the leaves. It is usually found on Sycamore, Maple, and Oak.
So what can be done: Monkeyman’s Tree Service suggests “sanitation,” which means raking and burning down fallen leaves to prevent the spores from overwintering. Early spring fungicide sprays may help to safeguard new growth.
2. Verticillium Wilt
Symptoms: Sudden wilting of branches, frequently on one side of the tree. Dark olive green sapwood streaks are visible when you peel off the bark.
Solution: There is no chemical treatment for the fungus after it is in the soil. We work on “stress management,” and deep-root fertilize the tree and water it regularly so it can tolerate the disease.
3. Dutch Elm Disease (DED)
Symptoms: Leaves on one branch may develop “flagging” with a yellowing and wilting in mid-summer. This is a very virulent variant of the vascular wilt.
So what can be done? The removal of infected branches must be done immediately. High-value trees will receive macro-infusion fungicide trunk injections to prevent infection by Monkeyman’s Tree Service.
4. Thousand Canker Disease (Black Walnut)
Caused by a fungus transported by the walnut twig beetle. Symptoms are represented by small “pin-sized” holes in the bark and thinning of the upper canopy.
What can be done: Early detection is key. Our emphasis is on keeping trees alive and in healthy condition, and in some instances, removing the tree to reduce the chance of the fungus spreading to other walnuts.
5. Armillaria Root Rot (Honey Fungus)
Identification: Look for clusters of honey-colored mushrooms at the base of the tree in autumn. Under the bark at the root flare, you will find white, fan-shaped fungal mats.
What can be done: We use “air-spading” to expose the root flare to oxygen, which can slow the fungus. If the tree is structurally unstable, removal is often necessary for safety.
6. Coryneum Blight (Shot Hole Disease)
Identification: Common in stone fruit trees (Cherry, Plum). It creates small reddish spots on leaves that eventually drop out, leaving a hole that looks like it was hit by a shotgun.
What can be done: Pruning during the dormant winter season and applying copper-based fungicides before bud break is the most effective treatment.
7. Needle Cast (Evergreens)
Hosts: Douglas Firs and Pines. Needles become reddish-brown and fall off, typically from the bottom of the tree to the top.
What can be done: This can be accomplished in at least two ways: Professional thinning and pruning improve air circulation, which will help to reduce the moisture that the fungus requires for growth.
8. Powdery Mildew
Leaves of Maples, dogwoods, and Lilacs are covered with a white, flour-like powder, which is called powdery mildew. It is very tolerant of warm, damp conditions and low air circulation.
Treatment: It is not usually fatal, but it can reduce the strength of the tree. During the growing season, horticultural oils or sulfur-based sprays are used to control the spread.
10. Oak Fruit Fly (S. leucocephala)
Signs of identification: “bleeding” cankers on the trunk exuding dark reddish-brown oozing sap. Can kill a mature Oak in a few weeks.
These are regulated pathogens, what can be done? Monkeyman’s Tree Service is also subject to strict quarantine procedures and can apply preventative phosphonate treatment to adjacent healthy trees.
11. Bacterial Canker
Common in Cherries, Maples. It produces oval wounded areas on the trunk, which often bleed a foul-odoured amber-coloured gum (gummosis).
Solutions: Cankers are surgically removed in dry periods when bacteria are not active and systemic antibiotics are administered to help the tree’s immune system control the bacteria.
What are the primary causes of tree illness?
Tree illness is rarely the result of a single isolated event; rather, it is typically caused by a combination of biological pathogens and environmental stressors that overwhelm the tree’s natural defenses. Monkeyman’s Tree Service categorizes these causes into two main groups: biotic (living) and abiotic (non-living) factors.
Biotic Causes (Living Pathogens and Pests)
- Fungal Pathogens: Fungi are the most common cause of tree illness, responsible for everything from leaf spots to deadly root rot. These organisms thrive in the damp Pacific Northwest climate, spreading through spores carried by wind, rain, or contaminated tools.
- Bacterial Infections: Bacteria can enter a tree through natural openings or wounds in the bark. Once inside, they can cause “fire blight” or bacterial cankers that disrupt the flow of nutrients and water.
- Insect Infestations: Pests like the Bronze Birch Borer or Aphids cause direct physical damage by feeding on leaves or boring into the wood. More importantly, many insects act as “vectors,” carrying diseases from a sick tree to a healthy one.
Abiotic Causes (Environmental Stressors)
- Nutrient Deficiencies: Trees require a specific balance of minerals to maintain their immune systems. A lack of nitrogen, iron, or magnesium in the soil can lead to chlorosis (yellowing) and increased susceptibility to disease.
- Soil Compaction and Poor Drainage: When soil is packed too tightly—often due to construction or heavy foot traffic – roots cannot access oxygen. This leads to “suffocation” and creates a perfect environment for root rot pathogens to take hold.
- Mechanical Damage: Improper pruning, lawnmower strikes, or “string trimmer blight” create open wounds in the tree’s protective bark. These wounds serve as entry points for pathogens that the tree would otherwise be able to resist.
- Climate and Weather Extremes: Sudden temperature fluctuations, prolonged drought, or excessive rainfall put trees in a state of chronic stress. A stressed tree redirects its energy from defense to basic survival, making it an easy target for opportunistic illnesses.
The Disease Triangle Concept
At Monkeyman’s Tree Service, we use the Disease Triangle to explain the cause of illness to our clients. For a tree to get sick, three things must be present simultaneously: a susceptible host (the tree), a virulent pathogen (the fungus or bacteria), and a favorable environment (such as a very wet spring). By altering even one of these factors—such as improving the environment through better drainage – we can often stop the illness from progressing.
What are the primary signs of tree disease to look for?
Homeowners should conduct a seasonal “walk-around” inspection of their property to check for signs of tree disease. Monkeyman’s Tree Service identifies the following as the most reliable indicators of a sick tree:
- Leaf Discoloration: Yellowing (chlorosis), browning (necrosis), or strange spotting on leaves outside of the autumn season.
- Cankers: Areas of dead or oozing bark on the trunk or branches, which often indicate a bacterial or fungal infection.
- Fungal Fruiting Bodies: The presence of mushrooms or “conks” growing directly on the trunk or at the base of the tree (the root flare).
- Stunted Growth: If a tree’s new spring growth is significantly smaller or sparser than in previous years, it is likely battling an internal illness.
- Early Leaf Drop: Trees that shed their leaves in mid-summer are often under extreme stress or suffering from a vascular infection.
How do you perform a professional tree disease diagnosis?
Diagnosis of a tree disease is more than a visual inspection; it requires a knowledge of the relationship between the host tree, the pathogen and the environment which may be referred to as the “Plant Disease Triangle”. Monkeyman’s Tree Service conducts a comprehensive examination that starts with the species of the tree — many diseases are tree species-specific.
Our arborists are able to assess the soil’s compaction, investigate for ‘girdling roots’ which could be causing the disease symptoms, and possibly collect samples of bark and/or leaves for laboratory examination. The diagnosis is crucial since the wrong treatment with a pesticide or a fungicide will not kill the tree and could even further suppress the tree’s ability to resist disease.
What are the most common sick tree symptoms?
Sick tree symptoms can be divided into “signs” (the actual pathogen, like a fungus) and “symptoms” (the tree’s physical reaction to the pathogen). Common symptoms include:
- Wilting: Even when the soil is moist, the leaves may droop because the tree’s internal “plumbing” is blocked.
- Dieback: The death of branches starting at the tips and moving toward the trunk.
- Epicormic Sprouting: Small, weak shoots growing directly out of the trunk, which is the tree’s “emergency” attempt to produce more foliage when the main canopy is failing.
- Thinning Canopy: A noticeable increase in the amount of light passing through the leaves, indicating a loss of foliage density.
How to save a diseased tree: Can it be done?
Knowing how to save a diseased tree depends entirely on the stage of the illness and the vitality of the specimen. Monkeyman’s Tree Service utilizes a multi-step recovery protocol:
- Sanitation Pruning: We remove infected branches using sterilized tools to prevent the illness from reaching the main trunk.
- Soil Amendment: Improving the soil biology through deep-root fertilization or vertical mulching helps the tree “outgrow” the infection.
- Targeted Injections: For vascular diseases, we can inject fungicides or antibiotics directly into the tree’s sapwood, providing faster results than soil drenches.
- Hydration Management: Stress is the primary driver of tree illness; ensuring the tree receives consistent, deep watering helps it maintain the energy reserves needed for defense.
What are the most effective tree fungus treatment options?
Tree fungus treatment must be timed perfectly with the life cycle of the fungus to be effective. Monkeyman’s Tree Service offers several professional-grade solutions:
- Foliar Sprays: These are applied early in the spring as leaves emerge to prevent fungal spores from attaching to the new growth.
- Systemic Fungicides: These chemicals are absorbed by the roots or injected into the trunk, circulating throughout the entire tree to fight internal infections like Dutch Elm Disease.
- Air Spading: If the fungus is attacking the roots (like Armillaria root rot), we use high-pressure air to uncover the roots, allowing them to dry out and slowing the fungal spread.
Why do trees get sick?
To truly understand tree illness, we must look at the synthetic sub-queries that drive tree health. Trees rarely get sick from a single cause; rather, it is a combination of stressors:
- Environmental Stress: Drought, extreme heat, or sudden late-season frosts weaken the tree’s natural chemical defenses.
- Mechanical Injury: Wounds from lawnmowers or improper pruning create “open doors” for bacteria and fungi to enter.
- Pest Vectors: Many tree illnesses are actually carried by insects. For example, various Bark Beetles introduce pathogens as they bore into the wood.
- Poor Site Conditions: Planting a sun-loving tree in the shade, or a tree that hates “wet feet” in a low-lying area, creates the chronic stress necessary for illness to take hold.
FAQ’s
Q1. Is it possible for a sick tree to get better?
Ans: Unlike humans, trees do not “heal,” but rather they “compartmentalize. This results in the development of a physical and chemical barrier around the infected region that isolates it.
Q2. Is a tree disease contagious to other plants?
Ans: Some fungal and bacterial diseases are very contagious and may be spread by wind, rain splash, or infected pruning tools.
Q3. How can I tell if my tree is sick or dead?
Ans: A quick test can be done by using the “scratch test”. Bark it off a twig—If the twig is green underneath, the branch is alive.
Q4. Is it possible for trees to become ill from overwatering?
Ans: Yes, overwatering can cause “root rot,” which is caused by the roots being submerged and anaerobic fungi attacking them.
Q5. What is all the white stuff on my tree’s leaves?
Ans: This is probably the “Powdery Mildew,” a common fungal disease that occurs in moist environments with poor aeration.
Is mulch a friend or foe to sick trees? Appropriate mulching will aid moisture retention. But mulching around the trunk (also known as “volcano mulching”) retains moisture and promotes decay.
Q6. When is it time to hire an arborist for an ailing tree?
Ans: Contact Monkeyman’s Tree Service immediately if the tree’s “canopy” (the top of the tree) becomes more than 10% discolored, or mushrooms grow on the trunk.
Q7. Can fertilizer cure a tree disease?
Ans: There’s a wrong side to fertilizer; if a tree has a leaf fungus, using high-nitrogen fertilizer can exacerbate the issue by inducing soft growth.
Q8. Are there different species of trees that are more susceptible to sickness?
Ans: Yes, some trees, such as Ash or Bradford Pear, are very susceptible to certain diseases and can kill the entire row of trees.
Q9. What is “Sudden Oak Death”?
Ans: Sudden Oak Death (SOD) is a debilitating disease that has wiped out millions of trees. It needs expert diagnosis and quarantine.
What Makes Monkeyman’s Tree Service for Disease Management so Special?
Monkeyman’s Tree Service offers tree disease identification and treatment in Portland, OR, and beyond by experts. We use Integrated Pest Management (IPM) principles and employ the most effective treatments available, based on scientific research in order to ensure the health of the ecosystem.
A sick tree is a burden, and many trees can be saved provided they receive the proper care. We have the knowledge and specialized equipment to diagnose exactly what is wrong with your landscape and offer you a roadmap to a healthy future. We don’t treat symptoms of the problem; we solve the problem in the environment where it occurs to keep your trees alive for years.
Call Monkeyman’s Tree Service today at (503) 358-8733 to schedule a tree disease diagnosis and learn how to save a tree on your property that has a disease.