Gumming

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

Canker-induced gummosis of Tibetan cherry (Rosser1954) Public Domain

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 how a specialized sap, or botanical gum, oozes out of an injury site or canker to provide protection.

Gumming is particularly common among stone fruits, such as nectarine and almond. It also occurs in mango and citrus.

Causes of gumming

Environmental stress, mechanical injury, insect attacks, and disease can all trigger a tree to start gumming. Gumming creates a protective barrier and may push any invaders out. You can use specific details surrounding gummosis to identify the problem. For example, gummosis caused by insect infestation or mechanical injury often exhibits 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, pruning, planting too deeply, excessive irrigation,, and  insufficient fruit thinning 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, leaf dieback, and stunting.

How to manage gumming

You can help your fruit and nut trees stay healthy by avoiding mechanical injuries, monitoring for pests and diseases, and regular feeding and irrigation. If you suspect disease has taken hold, scrape some of the bark from the area surrounding the gum. If you see discoloration or streaking, it is probably a disease that needs further attention. Removing affected branches can sometimes halt the progression of some diseases. Be sure to sanitize cutting tools between each cut with a household cleaner.

If the gum emerges from circular holes and contains insect larvae, the tree has the problem in hand. All you need to do is monitor the situation.