Gummosis is the discharge of a sticky, resinous gum from a peach tree’s bark or branches. This amber or clear sap is a defensive physiological response the tree uses to seal a wound, not an infection in itself. The oozing material signals that the tree has sustained an injury or is under stress. Understanding the underlying cause is the first step toward effective treatment, which involves surgical removal of damaged tissue and implementing long-term protective measures.
Identifying Gummosis and Determining the Cause
The appearance of the gum offers immediate clues regarding the source of the injury, which is necessary for choosing the correct treatment plan. The gummy substance typically appears as translucent droplets that harden into amber or dark brown masses on the trunk, main branches, or fruit. For successful remediation, the cause must be accurately identified, as treatment methods vary significantly.
Clear or translucent gum usually results from mechanical injuries, such as damage from lawnmowers, poor pruning cuts, or frost cracks. This clear sap indicates a purely physical wound where the tree is attempting to seal the opening with its natural resins and prevent the entry of secondary pathogens.
If the gummosis is concentrated near the soil line or on the lower trunk, and the sap is mixed with a sawdust-like material, the cause is likely the Peach Tree Borer (Synanthedon exitiosa). This reddish-brown, granular material is called frass, which is the excrement of the borer larvae feeding beneath the bark. This requires immediate, targeted physical removal of the pest.
When the gum is thick, dark amber, or yellow and accompanied by sunken, discolored patches of bark, the issue is often a fungal or bacterial canker. Pathogens like Cytospora or Botryosphaeria enter through existing wounds, killing the underlying tissue. Scraping away a small section of the bark will reveal discolored, dead wood beneath the canker, confirming the presence of dead tissue.
Immediate Physical Treatment of Affected Areas
Immediate treatment involves a surgical approach to remove damaged or infected tissue, giving the tree a fresh surface from which to heal. Begin by sanitizing all cutting tools, such as sharp knives or scrapers, with a solution of 70% rubbing alcohol or a 10% bleach solution. This sanitation step must be repeated between cuts and between trees to prevent spreading fungal or bacterial spores.
For cankers, carefully scrape away the gum and the infected, discolored bark until only healthy, cream-colored or green wood is exposed. This surgical removal should extend slightly past the visible margin of the canker to ensure all dead tissue is eliminated. Shape the final wound into a vertical oval or football shape with pointed ends. This design encourages the tree to quickly form a protective layer of callus tissue around the margins.
If the diagnosis points to the Peach Tree Borer, the larvae must be physically removed, a process known as “worming.” Gently use a thin, flexible wire or the tip of a small knife to probe the tunnel entrance within the gum pocket to pierce and kill the larva. Following removal, scrape away the remaining gum and damaged bark to fully expose the tunnel and ensure the pest is gone.
After the surgical removal is complete, all removed gum, diseased bark, and any visible larvae or frass must be collected immediately. This material contains pathogens or pests that can re-infect the tree or spread to other nearby trees. Place all debris into a sealed bag for disposal or burn it, ensuring it is destroyed rather than left on the ground near the tree.
Long-Term Recovery and Prevention Strategies
Once the affected areas have been surgically cleaned, the focus shifts to supporting the tree’s natural healing process and preventing future outbreaks. Experts advise against applying heavy tar-based wound sealants, as these can trap moisture and pathogens, hindering the natural formation of callus tissue. The wound should be left open to the air to dry and form its own protective barrier.
If the cause was a fungal or bacterial canker, a registered fungicide or bactericide may be applied directly to the freshly cleaned wound surface to suppress residual spores. This application is a protective measure for the exposed, healthy wood and is not a cure for established infection within the tree’s vascular system. Copper-based products are often used for bacterial issues, but they must be applied according to label instructions on dry bark.
Cultural practices are the most effective long-term defense against gummosis because they reduce the tree stress that makes it susceptible to infection.
Cultural Practices for Prevention
- Ensure the tree receives consistent, deep watering.
- Avoid excessive nitrogen fertilization that promotes easily damaged new growth.
- Prune only during dry weather, typically in late winter or early spring, to allow wounds to dry quickly.
- Prevent winter injury, as temperature fluctuations cause cracks that pathogens use for entry.
- Paint the lower trunk with a 50/50 mixture of white latex paint and water in the late fall to reflect sunlight.
Painting prevents the bark from warming up too quickly during the day and cracking when temperatures drop at night. Maintaining tree vigor through these practices allows the peach tree to effectively use its gummosis response to heal from minor injuries.