Gummosis is common on many fruit trees, particularly stone fruits, including cherries, peaches, plums, and apricots. This condition is characterized by the tree oozing a thick, gummy, or jelly-like sap from its bark, which often hardens into an amber or dark resin. Gummosis is not a disease itself but a symptom, representing the tree’s natural defense mechanism against underlying stress, injury, or infection. Observing this gummy exudate signals that prompt investigation and action are necessary to protect the tree’s long-term health and productivity.
Identifying the Root Cause
Successful treatment relies on accurately determining the cause of the gumming. The primary causes fall into three categories: fungal pathogens, insect infestations, and environmental stressors. Visual inspection of the site where the gum is emerging provides the initial clues for diagnosis.
Fungal infections, such as those caused by Leucostoma species, are a frequent cause of gummosis. Pathogen-induced gumming is often accompanied by a canker, which is a localized area of discolored, sunken, or dead bark. If you scrape away the outer bark, fungal canker reveals underlying tissue that is dead and typically tan or cinnamon brown, contrasting sharply with healthy, cream-colored wood. The gum from a fungal infection is usually yellow or amber-colored and will not contain any debris.
Insect damage, particularly from borers like the Peach Tree Borer, presents distinct signs. The gum is often mixed with fine, sawdust-like material, which is technically the insect’s excrement and wood shavings, known as frass. Borers typically attack the trunk near the soil line or the crotches of branches, and you may find a small entry or exit hole behind the gum mass. In contrast, gummosis caused solely by a non-living factor, such as mechanical injury or frost damage, often produces a clear or light-colored gum. If you scrape the bark away from a purely environmental injury, the inner tissue will remain healthy and light-colored.
Step-by-Step Treatment Procedure
Once the cause is identified, the active treatment process begins with preparation and sanitation. Sterilize all cutting tools, such as pruning shears or knives, by wiping them down with a 10% bleach solution or isopropyl alcohol before and after each cut. This prevents spreading fungal or bacterial spores to healthy parts of the tree or to other trees.
The next step involves the surgical removal of the infected tissue, known as canker excision. Using your sterilized tool, carefully scrape or cut away the dead, discolored bark and underlying wood until you reach healthy, clean tissue around the perimeter. Create a clean, vertically oval wound to encourage the tree to form a healing callus over the exposed area. If a borer is the cause, probe the tunnel with a thin, flexible wire to crush the larvae before cleaning the wound.
The cleaned wound should then be treated with an appropriate agent based on the diagnosis. For fungal causes, apply a commercial fungicide, such as a copper-based spray, directly to the exposed wood to control the remaining pathogen. If borers are confirmed, a targeted insecticide application containing ingredients like permethrin or spinosad may be necessary, timed according to the specific borer’s life cycle (often spring and late summer). After the surface has dried for several hours, leave the wound uncovered to allow for natural drying and healing. Heavy, tar-based wound sealants are generally discouraged as they can trap moisture and create a favorable environment for pathogens.
Post-Treatment Care and Prevention
Focusing on the tree’s overall health is the best way to prevent gummosis from recurring. Many fungal infections and borer attacks are opportunistic, targeting trees that are already weakened by stress. A primary focus should be on environmental adjustments, particularly correcting poor soil drainage, as waterlogged conditions favor root-rotting fungi like Phytophthora.
Proper watering techniques are also important. Avoid overwatering and ensure the soil has a chance to dry out between applications. Maintaining optimal soil pH, which for many fruit trees is around 6.5, can significantly improve the tree’s vigor and natural resistance to disease. Inspect the tree regularly for any new signs of gumming or slow wound healing, which indicates the issue may not be fully resolved.
Pruning practices also play a major role in prevention, as fresh cuts are a common entry point for pathogens. Stone fruits should be pruned during dry weather in late winter or early spring just before bud break, or in the summer, to allow the wounds to dry quickly and heal. Avoiding mechanical injuries from lawnmowers or string trimmers near the trunk is a highly effective preventative measure against creating new entry points for disease.