How to Treat Gummosis, or Bleeding in Tree Bark

It's not a death sentence, but it can weaken a tree

Gummosis on a cherry tree
Nazar Prosovych / Getty Images

Bleeding bark on trees and other woody plants often leads to concern when it's discovered by tree growers and yard tree owners. Gum or sap draining from a tree trunk or limbs is common in trees in the genus Prunus, which includes peaches and cherries, but it can happen in many species. This sap flow can be caused by biotic diseases, which are triggered by living organisms such as fungi, and abiotic injury, caused by non-living factors such as sunlight and temperature change.

One textbook definition gummosis is "the copious production and exudation of gum by a diseased or damaged tree, especially as a symptom of a disease of fruit trees." But it also can be an early symptom of other problems, not only in orchards but in prized landscape trees in yards, parks, and forests. 

Gummosis can weaken a tree, but it isn't the end of the world. Bleeding or oozing of sap from a tree, although not normal, won't necessarily permanently harm a tree or woody plant; most of them will survive. It's also important to remember that there are many causes for free-running sap from trees, including insect borers, cankers, bark injury, and a variety of diseases. Controlling these sources of damage will control gum deposits and sap flow, but there usually is no cure.

Causes

Gum exuding from cherry, peach, and sweetgum trees is common, so keep an eye on these species. Gummosis isn't a pathogen in itself but the response to environmental stress from pathogenic, insect, or mechanical injury.

Pathogenic infectious diseases and cankers that result in bleeding sap can become problematic in fruit orchards. Particularly, the cytospora canker, or perennial canker, commonly causes fungal bleeding in stone fruited trees such as apricot, cherry, peach, and plum.

This infection can be distinguished from insect damage and mechanical injuries because sawdust or pieces of bark aren't mixed in the sap, as would be the case with insect or mechanical damage. It isn't vital for you to identify the specific cause or causes involved, but it's very important to differentiate between insect infestation, mechanical injury, and infectious disease for diagnosis.

Prevention and Treatment

There are management practices you can follow to lower the risk of gummosis:

  • Be careful when using lawn and garden equipment to avoid tree tissue injury, which can harbor fungal spores.
  • Prevent winter cold injury to your tree by planting cold-hardy species within their hardiness zones and outside isolated wind avenues.
  • Maintain a tree's health to discourage boring insects.
  • Prune and dispose of limbs during late winter.
  • Try to identify whether the tree has been injured mechanically, been attacked by insects, or infected by a disease. Typically, mechanical injury and insects will leave exposed sapwood or sawdust.

Treat the causes as best you can while increasing the most "comfortable" tree conditions for optimal health. Increasing tree vigor is important and will yield great results. One helpful treatment is applying several pints of garden lime under the tree drip line if your site has a low to moderate PH. Raising soil Ph to 6.5 can do wonders for tree health.