How to stop tree sap
Under normal circumstances, trees drip sap as a way of protecting themselves when their bark has been damaged. If a tree is dripping sap, it is best to leave it alone unless it is an oak in the spring or an elm throughout the growing season.
Disrupting the natural healing process of a tree can sometimes cause more damage. Oaks and elms are particularly vulnerable to pathogens, however, and you should seal them when sap is dripping because of weather damage or pruning. It is important to seal the damaged area of the tree as soon as you notice it in order to protect the tree from pathogens.
Locate and identify the source of the dripping sap on the tree. Look for exposed wood where the bark has been torn off, broken or freshly pruned tree branches.
Shear off any damaged or broken limbs close the main boot at a 45-degree angle using pruning shears so that the cut is sloping downward. This will promote water drainage off from the cut.
Apply an even coat tree pruning sealant over the entire area of exposed wood on the tree where the sap is dripping. The sealant will immediately seal the wood and protect it.