Q. I have noticed what appears to be a gummy sap bleeding from areas where branches are attached on my flowering cherry tree. What’s going on?
A. Several homeowners recently have sent pictures of this sap bleeding on cherries and plums to me at the extension office. This condition you are observing is called gummosis.
The most serious type of gummosis is most often associated with fungal and bacterial pathogens that attack the tree. These pathogens can cause cankers – dead or diseased areas of the trunk and branches. This is what is happening in your case. The bleeding or gummosis you observe on your tree is most likely the response of the tree to a bacterial infection caused by Pseudomonas syringae. This strain is the most predominant in cherry and plum trees. When the weather is wet and cold, the gum can be produced in the cankers and eventually bursts through the bark and oozes down the trunk or branches of the tree. This is why you are seeing the bleeding at this time of year.
Over time, the cankers and bleeding may become more pronounced, as branches swell or form corky growths. Severe damage or infections may cause wilting of leaves and eventual death of fruit-bearing wood – or the entire tree.
The best way to prevent gummosis is to plant disease-resistant trees. If one has a tree exhibiting gummosis, the best strategy is to keep the tree as healthy as possible. Use compost or composted manure as a mulch, and keep mulch away (at least 6 to 12 inches) from the trunk of the tree. Prune under dry weather conditions.
It is vital that the tree has good drainage, so if water collects near the tree; divert the drainage to other areas. Do however, water the tree deeply and infrequently during periods of severe drought. Practice good sanitation by pruning and destroying cankered limbs.
Fixed coppers as well as Bordeaux mixture can be applied to the cankered areas in the fall and spring before bud break. According to the University of Idaho, small cankered areas can be also controlled by cauterization with a hand held propane burner in early to mid-spring. Hold the flame up to the canker for 15 to 20 seconds until the bark and underlying tissue begins to crackle and crinkle. If it is necessary, you can repeat this method in two to three weeks. Obviously, great care and concern for safety is needed if you attempt this process.
According to experts at the University of Tennessee and Iowa, gummosis can also be caused by a wide variety of other factors such as insects, mechanical damage, or weather.
In your case, the most likely cause is the bacteria that attacked the tree as a result of stress caused by the overly wet/dry conditions we have seen in recent years. The presence of gummosis is not necessarily a death sentence; often trees can survive for many years with this condition.