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The Green Thumb: Gummosis

An image of a peach tree dripping sap
USU Extension Forestry
USU Extension
An image of a peach tree dripping sap

Hi, my name is Kate Richardson and I'm the arthropod diagnostician here at USU.

One of the most common inquiries we get this time of year is, "Why is there sap oozing from my peach tree?" Gummosis is a general term describing the oozing of sap from a tree.

This can be caused by factors including insects, diseases or other abiotic causes. If the gummosis is clear, then the problem is likely abiotic or nonliving cause like mechanical damage from things like lawn mowers or pruners.

Trees are often nicked in prior seasons but won't display gumming until the spring when the trees wake back up from winter. Where this is the case there's usually little concern or need for treatment.

If the sap is milky dark or amber colored, it is more likely that the problem is caused by an insect or disease. The great peach tree borer is often blamed for sap oozing from branches. However, this insect typically only attacks the lowest 12 inches of the trunk.

Visual symptoms will include loose or dead bark and masses of gummy sap exuding from entry and exit holes at the base of the tree.

Similar deposits on the upper trunk or limbs are likely caused by fungal pathogens. When a tree is stressed from any of the previously mentioned reasons they are more susceptible to disease infection.

Fungal gumosis causes blisters and can lead to cankers. To most accurately identified the cause of gumosis contact your local county extension agent or the Utah plant pest diagnostic lab.