Gumming

Gumming does not mean your tree has lost its dentures. Instead, it is responding to injury.

Canker-induced gummosis of Tibetan cherry (Rosser1954)

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Unlike people and animals, plants do not have an active immune system. Instead, injured or infected areas are walled off to prevent further injury or the spread of infection or infestation. Gumming refers to the way a specialized sap, or botanical gum, oozes out of an injury site or canker to provide protection. ​

Cytospora canker on cherry (CO Extension)

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Gumming is particularly common among stone fruits, such as nectarine and almond, though is can also be seen on mango, citrus, and eucalyptus.


Causes of gumming

Environmental stress, mechanical injury, insect attacks, and disease can all trigger a tree to start gumming. This creates a protective barrier, as well as tries to push any invaders out. You can use specific details surrounding gummosis to identify the problem.

Bacterial spot on almonds (UCANR)

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For example, gummosis caused by insect infestation or mechanical injury will often exhibit bits of bark or sawdust mixed in with the gum. Look for other damage around the gumming site: Do leaves look sick or chewed upon? Has the bark’s integrity been breached? Do you see discoloration under the bark near the gumming?

• Environmental conditions such as sunscald, frost damage, improper pruning, planting too deeply, excessive irrigation, and over-bearing can all cause gumming.
• Mechanical injury by lawnmower collisions, rubbing branches, and outgrown tree supports can all lead to gumming.
• Insect infestation by peach tree borers, flathead borers, and other boring insects can cause gumming.
• Diseases such as Eutypa dieback, cytospora canker, Fusarium dieback, and bacterial spot may cause discoloration under the bark, as well as leaf dieback and stunting.

How to manage gumming

You can help your fruit and nut trees stay healthy by avoiding mechanical injuries, and monitoring for pests and diseases on a regular basis, along with proper feeding and irrigation. If you suspect disease, scrape some of the bark away from the area surrounding the gum. If you see discoloration or streaking, it is probably a disease that needs further attention. In many cases, diseases can be halted by removing affected branches below the infected area, just be sure to sanitize cutting tools between each cut.


If the gum emerges from circular holes and contains insect larvae, the tree is taking care of the problem itself, though further monitoring is a good idea.