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Ask the Master Gardener: Bleeding sap from cherry tree could be linked to several causes

By: Trish Grenfell, Placer County Master Gardener
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Question: My well established sour cherry tree is bleeding sap from its bark at several places on the tree. I assume this bleeding must be related to the flower/leaf drop that made my tree a skeleton of its former self. Most of the leaves turned yellow, brown and dropped. The tree losing sap must be like people losing blood. How do I stop it?
Answer: First of all, a tree’s sap is not the equivalent of a person’s blood, but sap bleeding on a tree is still not normal and the cause should be found. Since the sap is gummy, the term used for this discharge is gummosis and it is common on stone fruit trees, especially flowering/fruiting cherries.
The norm for years was to immediately blame insect larvae (the peachtree borer) when one found a bleeding cherry tree. This is a possibility since the cherry if the primary host plant for peachtree borer (go figure) and a symptom of this infestation is gobs of gum leaking from the tree.
However, the tree also bleeds from any break in the bark caused by cankers or mechanically created damage to the bark (i.e., chopping at the tree). To diagnose a borer, the bleeding would most likely be on or near the root crown, not higher than one foot above the ground.
The borer also leaves a trail of wood debris (frass) mixed in and around the oozing gum. The home gardener must apply for a permit from Placer County’s agricultural commissioner to spray the appropriate insecticide in spring. UC Davis recommends using pheromone traps to monitor adult emergence. And to also, “Keep tree bases free of vegetation to help reduce problems with peachtree borer, especially in the Central Valley. Heat and dryness reduce the survival of eggs and larvae.”
What if the gum is leaking out higher up on the trunk and there is no sign of any frass? It’s not the borer and you have ruled out a simple mechanical injury. There are three infectious organisms that can cause cankers on cherries and result in a gummosis response.
One is a bacteria in the genus Pseudomonas, which causes a disease known as bacterial canker. Another is a fungus that causes Leucostoma canker of Prunus. The third is usually called fungal gummosis and is caused by the fungus Botryosphaeria dothidea. In all three of these diseases, the key diagnostic feature is the canker.
A canker is a dead, often sunken lesion on a stem, branch or twig of a plant and can be identified by dead tissue immediately beneath and surrounding the point of gummosis.
Scraping away the gum and probing the bark beneath, you will find loose, crumbly bark and discolored tissue below.
In most cases the infected tree has been under environmental stress. For examples, the stress can be from a weak root system due to poor soil conditions or lack of nitrogen and microelements or drought stress or a cold injury, etc. True canker management is to prevent and treat the stress factors and keep the cherry trees healthy. Stress is a killer of plants and man.
But in the meantime, cut out cankers and destroy dead or damaged wood. Incomplete canker removal wastes time and money with little to no benefit in disease management.
Gardening questions? Call the Master Gardener Hotline at (530) 889-7388.