Infection by these organisms tend to cause circular cankers which have a depressed center rather than a conk or mushroom. The center of the canker is a brown punk. They will quite often form after a limb has been damaged or broken off. To reduce canker rots, remove any dead limbs or limb stubs in a tree. Prevent any injury to trees that might serve as an infection site.
Burls can occur on both oaks and hickories.
There are some swellings which occur on white oaks that aren't caused by a fungus but rather by the wood naturally growing over young buds and forming a gall or swelling. True burls can be removed by pruning or in some cases by surgery. They do little or no damage to trees. This is an important disease of all oaks. Members of the white oak group die very slowly after infection occurs and can carry the fungus in the vascular system without showing any symptoms.