Heart Rot - Bracket Fungus and Cavities
A large Cavity in a silver Maple caused by Heart Rot. Cavities in trees in forests are critical wildlife habitat and a good thing. Cavities in you tree over your neighbour's garage is another matter.
A saddle Fungus in a Silver Maple in mid October. Bracket Fungus such as this indicates the interior of the tree is rotting; and the bigger the tree , the more likely for structural failure.
Heart Rot Cavity at the base of a Norway Maple. This is as bad as it gets. Rot at the base of the tree means the tree is structurally unsound. The landowner needs to weigh risk to property and lives in deciding if this tree should be removed.
Heart Rot, Bracket Fungus and Tree Cavities are generally all related. Cavities in trees and Bracket Fungus are caused by something called Heart Rot. Heart Rot is whereby a fungus infects Heartwood of a tree. Heartwood is generally the non living interior part of the tree that provides support and strength for the trunk and branches. Heart Rot results in the wood rotting and turning into a soft pulp. So Heart Rot may not necessarily mean that a tree is in poor health but rotting wood in its interior means the tree is severely compromised as far as strength and prone to snapping or losing major branches. The Cavities occur when a combination of fungus, bacteria and animals decompose and remove the heart wood so only a cavity remains
Trees with open wounds, especially torn branches, are most susceptible to getting heart rot as the heartwood is exposed to the elements and allows for the fungus moving in. All trees can get heart rot and many such as Sugar Maple and Oak can usually close over the wound and the strength of the wood means these trees can close over the wound and the damage is low risk . However Silver Maple and Basswood are particularly susceptible to heart rot and rot can hollow out the main trunk quickly making the tree a high risk for failure.
By the time you notice bracket fungus or a cavity, the heart rot is fairly well established . There is no fungicide that effectively shuts the fungus down as the fungus goes deep into the trunk and the fungicide can't reach it. The best options to control heart rot once established is to A) reduce stress by summer watering during dry periods and/or fertilizing as this encourages callous growth and; B) take as much weight and size off the tree as possible to limit the risk of breakage and damage from a break ( yes this does expose the tree to more open wounds which could make the problem worse) . If you are lucky, the wound will completely close over with Callous wood. Another option is limit the amount of moisture and animals entering the cavities by closing the opening over . Arborists can apply hardeners over the wound/cavity to keep animals and moisture out and speed up the closure of the wound.
Ultimately heart rot means a weakened tree and the landowner needs to weigh the risks to property versus time and money invested managing the weakened tree.
One Last point. If you do see the tree starting to go into decline (generally die back at the top of the canopy )and the tree also has heart rot/cavities/bracket fungus you may want to consult an arborist to get an opinion about taking the tree down. Its best to get the tree down earlier rather than later for everyone's safety.
Note 1 : Carpenter Ants only eat wood that is rotting by way of a fungus. If you have carpenter ants odds are there is rotting cavities of wood somewhere nearby.
Note 2. The jury is still out on if Tree Wound Sealer that you buy at the store really works. Studies have shown mixed results as to effectiveness and you can actually make things worse if you apply the tar over fresh cuts thereby inhibiting the growth of necessary callous wood.