There is a little tree in the corner of my yard that has some sort of black fungus growing around the branches, almost like a tarry mold. Very gross looking.
There is another, larger tree nearby which is another species. Is this sort of thing contagious? Is there some sort of medicine that I could get for the ailing tree? Do I need to chop the little tree down to avoid contaminating the other tree? The larger tree’s branches hang very close to the sickly tree, and the it’s so large that it would be a bitch to cut down if it died.
This site has information on diseases, but you would need to know what kind of tree you have.
A general statement on wood rot from the site recommends completely removing the rotted wood and filling the cavity with a fungicide (which solution may not appeal to you since in your other thread you say you are trying to use organic gardening methods); use proper pruning; and remove wind damaged branches. The wood rot usually spreads through wounds, so if the other tree has broken branches then I imagine it can catch the disease.
Does the little tree look harmed by the mold? Often, black mold will grow on sugary secretions on plants (such as my grandmothers escalonia, which is often covered in sooty black mold). If Aphids are present, their sugary secretions often allow the mold to grow. If your little tree looks harmed, then you may want to take it out. I hear some trees are notorious for getting sooty black mold, such as walnuts, which are often hosts for aphids.