Gummosis – On Peach, Cherry, Plum

Q: What is happening to my plum tree? It finished bearing plums in July and now the trunk is a sea of sap! Should I do anything?

A: Gummosis is a general, though nonspecific condition of  cherry, peach and plum trees (both fruiting and flowering) in which gum is exuded through the bark. Gum is produced in response to any type of stress, not necessarily a wound, regardless of whether it is due to insects, mechanical injury, drought, cold injury or disease. Environmental stress is common.

TEMPERATURE My theory is that rapid winter temperature fluctuations often cause thin-barked plants, especially flowering cherries, to develop minute, barely visible cracks. The cracks partially reseal during cooler weather but then reopen and ‘bleed’ during summer when temperatures rise.

INJURY One of the best reasons to mulch around a tree isn’t to conserve moisture. It’s to keep lawnmowers and string trimmers at bay. Cherry trees have thin bark. When it is damaged by machinery or by kids climbing it while wearing their soccer cleats, sap will seep until the tree can wall off the injury internally.

CANKER When tree bark displays a generalized soft ooziness, gardeners christen it a canker. The canker can be bacterial or fungal in origin. Bacterial cankers usually have more “liquidity” than fungal cankers.

BORERS It is true that cherry borers can tunnel under the bark of a tree, causing sap to seep. In my experience, the sap that solidifies on the bark will have sawdust in it. When the hardened sap is dislodged a small hole will be visible in the bark, through which the liquid sap oozed originally. If there are several small pieces of sawdust in the gum, call your local Extension office (1-800-ASKUGA-1) for advice.

Gummosis very difficult to control on a single tree. Most often it is caused by stress or possibly by bacterial or fungal canker. Stress could be from drought stress, certain viruses, adverse growing sites, winter damage, herbicide damage, wounds, bruising of stem tissue, etc. but rarely from borers.

If  you want something to do about gummosis, you  can raise the pH in the soil around the roots.

To that end, in the absence of a soil test, sprinkle 1 cup of garden lime per inch of trunk thickness under the branch canopy every year for three years. This will raise the soil pH, which peaches/cherries/plums greatly appreciate.

Water the tree appropriately in summer so the roots are not damaged by drought.

See these links:

Excellent – Gummosis in Simple Terms

Here’s a good article on bleeding cherries


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