The sticky, gelatinous substance oozing from your peach tree is known as gummosis. This resinous material, which ranges from clear to dark amber, is not a disease but a visible symptom of underlying stress. Gummosis is the tree’s natural defense mechanism, producing gum to seal a wound in the bark and prevent the entry of pathogens or insects. The presence of this gum indicates the tree has suffered an injury and is actively trying to compartmentalize the damage.
Physical Damage and Environmental Stress
Physical forces often trigger this defensive gumming response. Mechanical injuries are common, resulting from accidental damage to the trunk or lower branches by lawnmowers or string trimmers. These wounds break the protective outer bark, allowing entry for fungal spores and causing immediate sap exudation. Improper pruning, such as flush cuts, also creates wounds the tree struggles to seal. Environmental stressors play a significant role, particularly sunscald, which damages bark on the south or southwest side of the trunk. Severe winter weather can also cause bark splitting and frost damage, leading to fissures that prompt gum production as a seal against infection.
Insect Pests That Cause Sap Oozing
When gummosis is caused by insect activity, the primary culprits are boring pests whose larvae tunnel into the wood. The Peach Tree Borer (Synanthedon exitiosa) is a major offender, with larvae attacking the trunk near or below the soil line. Borers create feeding tunnels that disrupt the vascular cambium, which the tree attempts to repair by flooding the area with gum. A key diagnostic feature of borer damage is that the exuded gum is typically mixed with reddish-brown frass (sawdust-like excrement). The Lesser Peach Tree Borer (Synanthedon pictipes) targets the upper trunk and scaffold limbs, causing similar gumming contaminated with frass. Identifying this gritty material within the sap is the quickest way to differentiate borer activity from other causes.
Fungal and Bacterial Diseases
Pathogens frequently exploit existing wounds, causing disease that manifests as gummosis. Cytospora Canker, caused by the fungus Leucostoma persoonii or L. cincta, is a widespread fungal disease affecting peach trees. This fungus invades the bark through injuries like pruning cuts or winter cracks, leading to the formation of cankers. These cankers are sunken, discolored areas of dead bark tissue that slowly expand, often girdling branches. The gum associated with Cytospora Canker is often dark amber and found on branches and the upper trunk, distinguishing it from borer damage. Bacterial Canker, caused by Pseudomonas syringae, is another source of gummosis in stone fruits. It often causes a milky or clear exudate with a slightly sour odor, particularly when infecting buds or young twigs during cool, wet spring conditions.
Practical Steps for Tree Recovery
Addressing gummosis requires minimizing stress and practicing sanitation. Pruning out severely infected or damaged wood removes the source of fungal spores, but cuts must be made cleanly into healthy tissue during dry weather. Sterilize pruning tools between cuts using alcohol or bleach to avoid transferring pathogens. Avoid applying wound paints or dressings, as these trap moisture and slow the tree’s natural healing process. Improve overall tree vigor through proper horticultural practices, including balanced fertilization and consistent, deep watering during dry periods. To prevent mechanical injury, install trunk guards around the base and maintain a weed-free zone clear of equipment. Consulting a certified arborist is advisable if the gumming is profuse, the trunk is heavily affected, or if the cause cannot be identified.