Something growing on my tree
Thanks for your question. This growth is fungi, one of an array of fungal organisms that invade trees through openings. The portion that is visible is the annual spore-releasing stage of the fungus. Since most fungi cannot breach a tree's defenses through bark, they blow in via wind to vulnerable areas. In this instance, the pruning cut and subsequent radial cracks within the wound provided opportunities for fungi to enter. Decay fungi live and grow by secreting enzymes onto organic matter, in this case the heartwood of the tree, and decomposing tissues, eventually compromising structural integrity. Mycologists (those who study the life cycle of fungi) assure us that what is on the outside of the tree is just the "tip of the iceberg", with a network of filaments and fungal tissues that have an extensive body within the tree. It is this depth of infection that makes treating with a fungicide infeasible and ineffective. Infected trees can live for a number of years but will eventually succumb to the fungus. For future info, be sure to start training trees at a young age so that no pruning cut exceeds ten inches across in any given direction. Trees with large pruning cuts are more prone to fungal infections before wounds have a chance to close. Tree best practices include watering during dry spells with 1 inch of water per week, applied all in one application; refrain from using lawn weed herbicides containing dicamba, which transfer to tree tissues; mulch with 2-4 inches of wood chips to a distance of 4 feet out from the tree (and not piled against the trunk); refrain from fertilizing the tree as this can cause greater virulence of the fungus; and hire a certified arborist to monitor the tree on a once-yearly basis to check structural integrity. Doing best practices will not "make" your tree survive but will help to prolong the life of the tree. As the years progress, the annual spore-releasing structure will most likely be larger than the previous year's. This is indicative of the continued growth and spread of the fungus within the tree and the reason for recommending annual visits by a certified arborist. Please let me know if you have further questions.