Understanding and Managing Gummosis: Solutions for Bleeding Trees
Learn the signs, causes, and solutions for gummosis—the oozing of sap from trees—so you can keep your landscape healthy.
Understanding Gummosis: Why Trees Bleed Sap
Gummosis refers to the unsightly and often worrying phenomenon where trees—especially members of the Prunus genus such as cherries, plums, peaches, apricots, and almonds—exude sticky, amber-colored sap from their bark. This condition can affect landscape trees, orchard fruit, and ornamentals, leading homeowners and gardeners to wonder what’s wrong and how best to intervene. While gummosis is typically a symptom rather than a disease in itself, addressing it requires careful diagnosis and proper management strategies.
What Is Gummosis?
Gummosis is the term used when gelatinous sap or gum leaks from wounds, cankers, or cracks in tree bark. This gum is a result of the tree’s natural defense mechanism, produced in response to a range of stresses, from environmental factors to pathogens and insect attacks.
- Commonly affects stone fruit trees: cherries, peaches, plums, apricots, and nectarines.
- Also seen in ornamental Prunus trees and various other species vulnerable to stress.
- The gum is typically amber, sometimes with brown or dark streaks, and can appear anywhere—from twigs and branches to the trunk base.
Main Causes of Gummosis
The presence of sap is a symptom, not a diagnosis. To treat or prevent gummosis, it’s crucial to understand its diverse causes:
- Environmental Stress: Drought, excessive moisture, nutrient deficiencies, or winter injury can prompt sap exudation.
- Mechanical Injury: Pruning wounds, animal damage, hail, and sunscald create openings for infection and increased stress.
- Insect Infestation: Borers such as the peach tree borer can tunnel into wood, causing local gum exudation.
- Infectious Diseases: Fungi and bacteria, especially the fungal pathogens Cytospora and Botryosphaeria, and the bacterium Pseudomonas, frequently cause cankers resulting in gummosis.
Key Symptoms and Identification
Identifying gummosis is straightforward, but recognizing the underlying cause takes observation and sometimes investigation:
- Exuding Amber Gum: Sticky sap appears on bark, often soft and golden when fresh, hardening to dark brown over time.
- Associated Lesions: The bark around gum sites may appear sunken (a sign of canker), cracked, or discolored.
- Other Clues: Presence of sawdust (frass) with gum points to insect borers, while the absence leans toward disease or injury.
- Additional Signs: Wilting, yellowing, or browning leaves, dieback of twigs or branches, and even whole-branch death if infections are severe.
How to Differentiate Between Causes
| Symptom/Sign | Possible Cause | Diagnosis Tips |
|---|---|---|
| Gum with sawdust or black specks | Insect borer infestation | Look for small holes, frass, and tunneling under bark |
| Gum from wounds or pruning cuts | Mechanical injury or fungus entry | Check if cut or injured area is clean or has sunken, dead bark |
| Gum with sunken, discolored bark patches | Fungal or bacterial canker | Peel back bark; if wood underneath is brown/dead, likely disease |
| Multiple small gum spots after harsh winter | Winter or frost damage | Check for bark splits and frost cracks |
| Generalized gum, tree otherwise healthy | Stress or environmental shock | Consider drought, heavy rain, or poor site conditions |
Common Fungal and Bacterial Diseases Causing Gummosis
While several factors can trigger gummosis, some of the most destructive are canker diseases. Below are the leading disease culprits:
- Cytospora Canker (Leucostoma canker)
This fungal disease targets bark wounded by pruning, winter injury, or other means. The Cytospora fungus invades these weakened areas, killing bark and underlying wood. The tree oozes gum at the infection site, which may then dry and darken. Early infection may result in sunken, cinnamon-brown lesions, and as the canker expands, large sections of bark may die, leading to dieback of branches or complete tree loss. Cytospora is a leading cause of gummosis in stone fruit orchards and backyard gardens.
- Botryosphaeria-induced Fungal Gummosis
This fungus infects trees already under environmental stress and is common in cherries and other Prunus species. It leads to sunken cankers and the production of large amounts of gum. Management is challenging once the disease is established.
- Bacterial Canker (Pseudomonas syringae)
This bacterial infection affects a range of stone fruits, most notably cherries. It usually enters through pruning or frost injuries. Gummosis often appears along with blackened, water-soaked bark and rapid dieback of twigs.
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Insect and Mechanical Damage
Tree borers and mechanical injuries are frequent triggers for gummosis:
- Peach Tree Borer: This insect attacks the lower trunk of peaches, cherries, apricots, and related trees. The larva tunnels into wood, and the tree responds by exuding large quantities of gum, often mixed with sawdust and larval excrement (frass).
- Other Borers: Various beetles and moths can create similar wounds, especially in stressed or damaged trees.
- Mechanical Injury: Improper pruning, lawn mower wounds, animal chewing, and accidental bark scraping are frequent causes of sap flow. While most trees can recover, these wounds may offer entry points for disease.
Environmental and Cultural Stressors
- Drought and Poorly Drained Soil: Stress from lack of water or waterlogged roots causes bark cells to die and increases vulnerability to infection.
- Winter Damage: Frost cracks and sunscald on trunks are often followed by gummosis—especially after harsh winters on young or thin-barked trees.
- Nutrient Deficiency: Poor soil nutrition weakens trees making them more susceptible to injury and disease.
Managing and Treating Gummosis
Once gummosis occurs, options for treatment are somewhat limited, especially if the root cause is advanced disease or internal damage. However, several strategies can minimize harm and prevent future outbreaks:
1. Prune and Remove Infected Wood
- In late winter or early spring, before bud break, remove all visibly infected limbs and twigs.
- Always cut well below the canker, into healthy green tissue; disinfect tools between cuts using bleach solution or rubbing alcohol.
- Do not perform major pruning during wet weather or when trees are actively growing as wounds are slow to heal during these times.
- Destroy infected branches—do not compost—to prevent the spread of spores.
2. Address Tree Stress
- Maintain consistent watering, especially for young or recently transplanted trees.
- Mulch trees to conserve soil moisture and reduce competition from weeds.
- Fertilize appropriately based on a soil test to provide a balanced nutrient profile.
- Protect trunks from mechanical damage using trunk guards or mulch rings kept away from bark.
- Whitewash lower trunks (using a 50/50 mix of white latex paint and water) in winter to prevent sunscald.
3. Prevent Infections
- Time all pruning to dry periods, preferably late winter or early spring, so wounds heal rapidly.
- Avoid pruning during or immediately after rain, which spreads fungal spores.
- Immediately treat or wrap any large bark wounds to facilitate proper healing.
- Regularly monitor trees for early signs of decline, cankers, or insects.
4. Control Insect Problems
- Inspect lower trunk and base regularly for evidence of borers (holes, gum with sawdust, larvae).
- Apply recommended borer controls if detected; consult local extension for appropriate pesticides and timings.
- Remove and replace trees suffering repeated borer infestations or severe decline.
Fungal and Bacterial Disease Management Tips
- There is no effective chemical cure for canker diseases once established in woody tissue.
- Routine sanitation—removing infected tissues, promptly discarding prunings—significantly reduces spread.
- Some fungicides may provide limited protection when applied preventively during high-risk periods, but effectiveness is modest and must be part of an integrated program.
- Plant resistant tree varieties if available, or choose alternative species for high-disease-pressure sites.
Prevention: Best Practices for Healthy Trees
- Choose planting sites with good air circulation, sun exposure, and well-drained soil.
- Avoid planting stone fruit trees where canker has previously occurred or in poorly drained soils.
- Apply mulch 2-3 inches deep around the tree (not against the trunk) to conserve moisture and protect roots.
- Train branches early to prevent narrow crotch angles (where cankers easily develop).
- Manage irrigation to avoid drought or excessive wetness—drip systems work well.
When to Remove Severely Affected Trees
- If trunk cankers encircle or girdle the main stem, or if repeated dieback continues despite intervention, it may be best to remove the tree to protect others nearby.
- Dispose of the tree away from the site, or burn if permitted, to break the disease/insect cycle.
Frequently Asked Questions (FAQs)
Q: Is gummosis dangerous for all trees?
No, gummosis is most common and problematic in stone fruit trees, especially those in Prunus. It may occur in other species but rarely leads to severe decline outside vulnerable hosts.
Q: Can trees recover from gummosis?
If caused by temporary stress or minor injury, and with proper care and removal of infected wood, trees can recover or contain the problem. Chronic disease or borer infestation reduces the chance of long-term survival.
Q: Will pruning alone stop gummosis?
Pruning infected twigs and branches helps but must be combined with addressing stress, preventing reinjury, and monitoring for pests and disease. Pruning is not a cure for infected trunks or advanced cankers.
Q: Should I use sealants or paint on pruning wounds?
Generally, wound dressings are not recommended except for large, high-risk wounds in high-disease areas. The best defense is correct pruning and overall tree vigor.
Q: Are chemicals effective against gummosis?
No curative chemicals are available once disease is established. Preventive sprays or trunk paints may offer limited protection and are most useful as part of a comprehensive cultural program.
Summary Table: Key Points for Managing Gummosis
| Action | Effectiveness | Best Timing |
|---|---|---|
| Remove infected wood | High | Late winter/early spring |
| Maintain tree vigor (water, nutrition, mulch) | High | Year-round |
| Monitor & control pests/borers | Medium-High | Growing season |
| Protect trunks (paint, guard, mulch ring) | Medium | Winter |
| Site selection and planting resistant varieties | Very High | Planting time |
References and Further Reading
- Land-Grant University Plant Disease & Diagnostic Labs: Gummosis Fact Sheets
- State Extension Bulletins on Cytospora, Canker Diseases, and Fruit Tree Care
- National Gardening Association, Missouri Botanical Garden, and University Pest Advisories
If you notice sap leaking from your tree, resist the urge to panic. Remember, gummosis is typically a reaction to stress or damage. Through attentive care—pruning, stress reduction, good site maintenance, and regular monitoring—you can significantly reduce the impact of gummosis and keep your fruit and ornamental trees thriving for years to come.
References
- https://plantsciences.tennessee.edu/wp-content/uploads/sites/25/2021/10/Gummosis_in_Prunus.pdf
- https://pestadvisories.usu.edu/2024/04/04/gummosis-2/
- https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/insects-pests-and-problems/diseases/cankers/gummosis-of-fruit-trees
- https://gardenerspath.com/how-to/disease-and-pests/gummosis-in-fruit-trees/
- https://ipm.ucanr.edu/agriculture/citrus/phytophthora-gummosis/
- https://www.youtube.com/watch?v=9W6iCMBLLmU
- https://www.phillyorchards.org/2017/08/03/bacterial-and-fungal-canker/
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