Black Tar Like Substance on Trees (5 Arborist Clues)

Aha! I remember it like it was yesterday. I was knee-deep in sawdust, splitting a particularly stubborn oak log, when a neighbor wandered over, a worried look etched on his face. “I’ve got this…stuff,” he said, gesturing vaguely towards his property line. “Black, gooey, looks like tar…all over my trees. What is it?”

That moment sparked a deeper dive into the world of tree diseases and conditions than I ever anticipated. It turns out, that “black tar” can be a sign of several different issues, some relatively harmless, others a serious threat to the health of your trees and even the safety of your property. So, let’s get to it.

What Does “Black Tar” Actually Mean?

The term “black tar” is a general descriptor, not a specific diagnosis. It can refer to various substances, each with a different cause and requiring a different approach. We need to play arborist detective, using clues to narrow down the possibilities.

5 Arborist Clues to Unravel the Mystery

Here are five key clues I use when assessing a tree with this symptom, along with the potential causes they point to:

1. Location: Where on the tree is the “tar” located?
2. Texture: What does the substance feel like? Is it hard, soft, sticky, or brittle?
3. Host Tree: Which species of tree is affected?
4. Associated Symptoms: Are there other signs of disease or damage, such as dieback, cankers, or insect activity?
5. Seasonality: When did you first notice the substance?

Now, let’s explore these clues in detail.

Clue #1: Location, Location, Location

The location of the black tar-like substance can provide significant clues about its origin.

• Trunk: If the “tar” is primarily on the trunk, especially near the base, it could indicate:
  • Wetwood (Slime Flux): This is a bacterial infection that causes fermentation within the tree. The pressure from this fermentation forces sap, often dark and foul-smelling, to seep out of cracks and wounds. It’s common in elms, poplars, and willows. I’ve seen this a lot on older cottonwoods I’ve taken down for firewood. It makes them smell absolutely awful, and the wood is often waterlogged.
  • Phytophthora Root Rot: While not directly producing “tar,” the disease can cause oozing cankers near the base of the trunk, which can appear dark and messy. This is more common in poorly drained soils. I lost a beautiful apple tree to this a few years back. The ground was just too wet during the spring.
  • Mechanical Damage: Wounds from lawnmowers, vehicles, or even animals can create entry points for decay and subsequent sap flow, which can darken and resemble tar. I always preach keeping a good distance between the mower and tree trunks.
• Branches: “Tar” on branches might suggest:
  • Cytospora Canker: This fungal disease commonly affects stressed trees, particularly stone fruits (like cherries and plums) and spruces. It causes sunken, discolored cankers that may ooze sap. I’ve seen it particularly bad on Colorado Blue Spruce that are planted too close together.
  • Insect Infestations: Certain insects, like aphids and scale insects, produce honeydew, a sugary substance that can attract sooty mold. Sooty mold is a black fungus that grows on the honeydew, giving the appearance of “tar.” I’ve battled aphids on my apple trees for years. A strong blast of water from the hose often does the trick.
• Leaves: If the black substance is primarily on the leaves, it’s highly likely to be:
  • Sooty Mold: As mentioned above, sooty mold grows on honeydew excreted by insects. It’s usually a cosmetic issue but can reduce photosynthesis if the coating is heavy.

Clue #2: Texture Tells a Tale

The texture of the substance is another critical piece of the puzzle.

• Sticky and Gooey: This often points to sap flow, either from:
  • Insect Activity: Honeydew is typically sticky.
  • Wound Response: Trees naturally produce sap to seal wounds. This sap can sometimes become infected or discolored.
  • Wetwood: The sap associated with wetwood is often sticky and foul-smelling.
• Hard and Brittle: This might indicate:
  • Dried Sap: Sap that has been exposed to air for an extended period will harden and become brittle.
  • Fungal Growth: Some fungal growths, particularly older ones, can become hard and brittle.
• Soft and Slimy: This is often associated with:
  • Bacterial Infections: Wetwood is a prime example.
  • Early Stages of Fungal Growth: Some fungi start as a soft, slimy mass.
• Resinous: This suggests:
  • Conifer Response: Conifers, like pines and spruces, produce resin to protect themselves from injury and insects. Excessive resin flow can indicate a problem.

Clue #3: Host Tree: Know Your Species

Different tree species are susceptible to different diseases and pests. Knowing the type of tree affected is crucial for diagnosis.

• Stone Fruits (Cherry, Plum, Peach): Cytospora canker is a common problem.
• Elms, Poplars, Willows: Wetwood is frequently seen in these species.
• Pines and Spruces: Look for signs of bark beetles or other conifer-specific pests. Excessive resin flow (“pitching out”) is a red flag.
• Oaks: Oak wilt, although not always presenting as “tar,” can cause sap oozing and is a serious concern.
• Maples: Verticillium wilt can cause dieback and sap staining.

I once spent a frustrating afternoon trying to diagnose a problem on a neighbor’s tree, only to realize I was barking up the wrong tree – literally! I was treating it like an oak, but it turned out to be a very oddly shaped maple. Accurate identification is key.

Clue #4: Associated Symptoms: The Bigger Picture

Don’t just focus on the “tar.” Look for other symptoms that might provide clues.

• Dieback: Are branches dying back? This could indicate a vascular disease like Verticillium wilt or a canker disease.
• Cankers: Sunken, discolored areas on the bark are often signs of fungal infections.
• Leaf Discoloration or Spotting: This could indicate a fungal or bacterial leaf disease.
• Insect Activity: Look for signs of boring insects, such as small holes in the bark or sawdust-like frass.
• Wilting: Sudden wilting can be a sign of root problems or vascular diseases.
• Unusual Leaf Drop: Premature or excessive leaf drop can be a sign of stress or disease.

One time, a client called me about “black tar” on their cherry tree. But upon closer inspection, I noticed tiny holes in the bark and sawdust-like material. It turned out the tree was infested with borers, and the “tar” was a combination of sap and frass.

Clue #5: Seasonality: Timing is Everything

When you first noticed the “tar” can also be helpful.

• Spring: Sap flow is more common in spring as trees begin to actively grow. This is also when many fungal diseases become active.
• Summer: Insect activity is often at its peak in summer, so sooty mold is more likely to appear.
• Fall: As trees prepare for winter, they may be more susceptible to stress and disease.
• Winter: Cankers may be more visible in winter when leaves are absent.

I remember one winter noticing a lot of sap oozing from a maple tree. It turned out to be frost cracking – the sudden temperature changes caused the bark to split, leading to sap flow.

Common Culprits Behind “Black Tar”

Now that we’ve explored the clues, let’s look at some of the most common causes of “black tar” on trees:

1. Wetwood (Slime Flux)

• Cause: Bacterial infection.
• Symptoms: Foul-smelling, dark, slimy sap oozing from cracks and wounds on the trunk.
• Affected Trees: Elms, poplars, willows, cottonwoods.
• Treatment: There’s no cure for wetwood. Focus on maintaining tree health and preventing further stress. Ensure proper watering and fertilization. Prune dead or diseased branches to improve air circulation. Avoid wounding the tree.
• Firewood Implications: Wood from trees with wetwood is often waterlogged and difficult to dry. It can also have an unpleasant odor. I generally avoid using it for firewood if possible.

2. Cytospora Canker

• Cause: Fungal disease.
• Symptoms: Sunken, discolored cankers on branches, often oozing sap. Dieback of branches above the canker.
• Affected Trees: Stone fruits (cherry, plum, peach), spruces, willows.
• Treatment: Prune out infected branches well below the canker. Disinfect pruning tools between cuts to prevent spreading the disease. Maintain tree health by providing adequate water and fertilization. Avoid stressing the tree.
• Firewood Implications: Cankered wood may be weaker and more prone to splitting. Burn it as soon as possible to prevent further fungal growth.

3. Sooty Mold

• Cause: Fungal growth on honeydew excreted by insects (aphids, scale insects).
• Symptoms: Black, sooty coating on leaves and branches.
• Affected Trees: Wide range of trees.
• Treatment: Control the insect infestation. Horticultural oil or insecticidal soap can be effective. Wash off sooty mold with water.
• Firewood Implications: Sooty mold is primarily a cosmetic issue and doesn’t usually affect the quality of firewood.

4. Insect Infestations (Borers, Bark Beetles)

• Cause: Various insect species.
• Symptoms: Small holes in the bark, sawdust-like frass, sap oozing, dieback.
• Affected Trees: Varies depending on the insect species.
• Treatment: Identify the insect and use appropriate insecticides or biological controls. Remove severely infested trees.
• Firewood Implications: Wood from infested trees may be weakened and contain insect larvae. It’s best to burn it as soon as possible to prevent the insects from spreading. I always make sure to burn wood from trees that are known to have Emerald Ash Borer issues before the spring.

5. Mechanical Damage

• Cause: Wounds from lawnmowers, vehicles, animals, etc.
• Symptoms: Open wounds on the trunk or branches, sap oozing, decay.
• Affected Trees: Any tree.
• Treatment: Clean and protect the wound. Remove any loose bark or debris. Apply a tree wound dressing if desired (although some arborists argue against this). Protect the tree from further damage.
• Firewood Implications: Wood near the wound may be decayed and weaker.

6. Phytophthora Root Rot

• Cause: Soilborne fungal-like organism.
• Symptoms: Wilting, yellowing leaves, dieback, cankers near the base of the trunk that may ooze sap.
• Affected Trees: Wide range of trees, especially those in poorly drained soils.
• Treatment: Improve soil drainage. Apply fungicides specifically for Phytophthora. Avoid overwatering. Remove severely infected trees.
• Firewood Implications: Wood from trees with root rot may be waterlogged and difficult to dry.

Taking Action: From Diagnosis to Treatment

Once you’ve identified the likely cause of the “black tar,” it’s time to take action. Here’s a step-by-step guide:

1. Confirm the Diagnosis: If you’re unsure of the cause, consult with a certified arborist. They can provide a professional diagnosis and recommend appropriate treatment options. Look for an ISA Certified Arborist in your area.

2. Develop a Treatment Plan: The treatment plan will depend on the specific problem. It may involve pruning, insect control, fungicide applications, soil amendments, or simply improving tree care practices.

3. Implement the Treatment Plan: Follow the recommended treatment plan carefully. Use appropriate tools and equipment, and always follow safety precautions.

4. Monitor the Tree’s Health: Regularly monitor the tree’s health to see if the treatment is working. Look for signs of improvement, such as new growth and reduced sap flow.

5. Prevent Future Problems: Take steps to prevent future problems by maintaining tree health, protecting trees from damage, and choosing disease-resistant varieties.

Tools of the Trade: Chainsaws, Axes, and More

In my experience, having the right tools is essential for effective tree care and firewood preparation. Here are some of my go-to tools:

• Chainsaws: A good chainsaw is indispensable for pruning, felling, and bucking logs. I use a Stihl MS 261 C-M for most of my work. It’s powerful, reliable, and relatively lightweight. For larger trees, I might use a Stihl MS 462 R C-M. Make sure you have the proper personal protective equipment (PPE) – helmet, eye protection, ear protection, gloves, and chaps.
  • Chain Selection: Different chains are designed for different types of wood. For hardwoods like oak and maple, I use a full-chisel chain. For softer woods like pine and spruce, I use a semi-chisel chain.
  • Chain Sharpening: A sharp chain is essential for safe and efficient cutting. I sharpen my chains regularly using a chainsaw file and guide.
• Axes: An axe is useful for splitting small logs and removing branches. I have a few different axes, including a splitting axe for larger logs and a felling axe for smaller trees. The Gransfors Bruks splitting maul is a favorite.
• Log Splitters: For splitting large quantities of firewood, a log splitter is a lifesaver. I use a hydraulic log splitter with a 25-ton capacity. It makes splitting even the toughest hardwoods a breeze.
  • Safety: Always wear eye protection and gloves when using a log splitter. Keep your hands clear of the splitting wedge.
• Pruning Shears and Loppers: These are essential for pruning small branches and twigs. I use Felco pruning shears and loppers – they’re durable and reliable.
• Hand Saw: A hand saw is useful for making precise cuts, especially when pruning.
• Wedges: Wedges are used to prevent the saw from binding when felling trees. I use both plastic and metal wedges.
• Measuring Tape: A measuring tape is essential for accurately measuring logs and firewood.
• Moisture Meter: A moisture meter is used to measure the moisture content of firewood. This is crucial for ensuring that the wood is properly seasoned before burning. I target a moisture content of 20% or less for optimal burning.
• Personal Protective Equipment (PPE): This includes a helmet, eye protection, ear protection, gloves, chaps, and steel-toed boots. Safety should always be your top priority.

Firewood Preparation: From Tree to Hearth

If the affected tree needs to be removed and is suitable for firewood, here’s my process:

1. Felling: Carefully fell the tree, taking into account the lean, wind, and surrounding obstacles. Use proper felling techniques to ensure the tree falls safely and predictably.
   • Hinge Wood: Maintaining proper hinge wood is crucial for controlling the direction of the fall.
   • Back Cut: The back cut should be slightly above the level of the horizontal cut.
2. Bucking: Cut the tree into manageable log lengths (typically 16-18 inches for most wood stoves).
3. Splitting: Split the logs into pieces that are small enough to fit into your wood stove or fireplace.
4. Stacking: Stack the firewood in a well-ventilated area to allow it to dry. I prefer to stack my firewood in rows, with air gaps between the rows.
   • Stacking Method: A good stacking method promotes airflow and prevents the wood from rotting.
5. Seasoning: Allow the firewood to season for at least 6-12 months, or longer for hardwoods. Seasoning reduces the moisture content of the wood, making it easier to burn and producing more heat.
   • Drying Time: The drying time depends on the type of wood, the climate, and the stacking method.

Case Study: The Mystery of the Oozing Oak

I once had a client who was very concerned about a large oak tree in their backyard. The tree had several areas of black, tar-like substance oozing from the trunk. The client feared it was oak wilt, a deadly disease that can quickly kill oak trees.

I examined the tree carefully, looking for the telltale signs of oak wilt – leaf discoloration, wilting, and vascular staining. However, I didn’t find any of these symptoms. The “tar” was located primarily around old wounds on the trunk, and the tree appeared to be otherwise healthy.

After further investigation, I determined that the “tar” was simply sap that was oozing from the wounds and becoming discolored. The wounds were likely caused by mechanical damage from a lawnmower.

I cleaned the wounds and applied a tree wound dressing. I also recommended that the client protect the tree from further damage. The tree recovered fully and is still thriving today.

This case highlights the importance of careful diagnosis. The “black tar” was alarming, but it turned out to be a relatively minor problem that was easily resolved.

The Economics of Firewood: A Sustainable Resource

Firewood can be a sustainable and cost-effective heating option, especially if you have access to trees on your property. However, it’s important to consider the economics of firewood production.

• Cost of Equipment: Chainsaws, axes, log splitters, and other tools can be expensive.
• Time and Labor: Cutting, splitting, stacking, and seasoning firewood takes time and effort.
• Fuel Costs: If you’re using a chainsaw or log splitter, you’ll need to factor in the cost of fuel.
• Transportation Costs: If you’re transporting firewood, you’ll need to factor in the cost of transportation.

Despite these costs, firewood can still be a more economical option than other heating sources, especially if you can harvest the wood yourself. Plus, there’s something deeply satisfying about heating your home with wood you’ve harvested and prepared yourself.

Safety First: A Non-Negotiable Priority

Working with trees and firewood can be dangerous. It’s crucial to prioritize safety at all times.

• Wear appropriate PPE: Always wear a helmet, eye protection, ear protection, gloves, chaps, and steel-toed boots.
• Use tools properly: Follow the manufacturer’s instructions for all tools and equipment.
• Be aware of your surroundings: Watch out for falling branches, uneven terrain, and other hazards.
• Work with a partner: It’s always safer to work with a partner, especially when felling trees.
• Take breaks: Don’t work when you’re tired or fatigued.
• Know your limits: Don’t attempt tasks that are beyond your skill level.
• First Aid: Keep a well-stocked first aid kit on hand.
• Emergency Plan: Have an emergency plan in case of an accident.

I’ve seen too many accidents happen in the woods. Don’t let it happen to you. Take safety seriously.

Looking Ahead: Sustainable Forestry Practices

As someone deeply involved in wood processing, I feel a responsibility to promote sustainable forestry practices. This means managing forests in a way that meets the needs of the present without compromising the ability of future generations to meet their own needs.

• Selective Harvesting: Choose trees for harvest that are mature, diseased, or damaged. Leave healthy trees to continue growing.
• Reforestation: Replenish harvested areas with new trees. Choose tree species that are well-suited to the site and climate.
• Forest Management Plans: Develop and implement forest management plans to ensure the long-term health and productivity of your forests.
• Reduce Waste: Minimize waste by using all parts of the tree, including branches and tops. These can be used for firewood, mulch, or other products.
• Support Sustainable Forestry: Buy wood products from companies that practice sustainable forestry. Look for certifications like the Forest Stewardship Council (FSC).

By adopting sustainable forestry practices, we can ensure that our forests continue to provide us with wood, clean air, clean water, and other valuable resources for generations to come.

Next Steps: Putting Knowledge into Action

Now that you’ve learned about “black tar” on trees, it’s time to put your knowledge into action. Here are some next steps you can take:

1. Inspect your trees: Take a walk around your property and inspect your trees for signs of “black tar” or other problems.
2. Identify the tree species: Use a tree identification guide or app to identify the species of trees on your property.
3. Consult with an arborist: If you’re unsure of the cause of the “black tar” or how to treat it, consult with a certified arborist.
4. Develop a tree care plan: Develop a tree care plan for your property, including regular pruning, fertilization, and pest control.
5. Prepare for firewood season: If you plan to use firewood for heating, start preparing for the firewood season now. Cut, split, stack, and season your firewood well in advance.
6. Learn more about sustainable forestry: Read books, articles, and websites about sustainable forestry practices.
7. Get involved in your local community: Join a local tree planting or conservation group.

The world of trees is fascinating and rewarding. By learning about tree health, firewood preparation, and sustainable forestry, you can become a better steward of the environment and enjoy the many benefits that trees provide.

So, go out there, inspect your trees, and start putting your knowledge into action. And remember, when in doubt, consult with a professional! Your trees will thank you for it.

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