Question
Hello from upstate new york.  My father has a farm with several woodlots on it.  In one of the woodlots there is a large population of hickory trees.  Every year more and more of them grow these black ugly fungi.  Usually they grow where a limb forks or where the limb is attached to the tree, but they seem to choke of the limb and eventually the limb will die and fall off.  Now they keep spreading to new trees, and i think it only takes 2 or 3 years for a tree that has them to die.  I was wondering what they are exactly and what the best way to control the spread of the fungi.  They are black and as hard and dense as the hickory itself.  We are planning on to cut down every tree that shows signs of infestation this summer, i wonder if this is the best way to go about it, or is there a certain time of year that is better.  Moreso, will the fungus continue to spread if we leave the limbs in the woods or does something more need to be done.  Any information that you would have would be much appreciated.  Thank you!

Answer
This sounds like a decay fungi called Inonotus obliquus. But there are several fungi that fit the decay type. Like all decay fungi the main fungi lives on the enter wood of the tree and the fruiting bodies are the outer sign of the decay (the black conks on the bark. The decay fungi eats away at the enter woody cells and spread up the trunk. This process tales many years to reach the limbs. When limbs begin to break off on large trees the first guess would be the decay type fungi. There are many that can infest trees but all work about the same way. The end of the branch broken off  near the trunk should show sign of not being hard solid wood. Decay fungi will not kill trees but over time will cause them to become hollow and start to break up--limbs falling. I would call the State Forestry agency and ask one of their Foresters to come take a look and advise you on the best thing to do. IF the trees are in a place that if one should fall it would not damage anything you may just want to leave them be and enjoy them but if the trees will damage something below then you may want to remove them. It is a fairly complicated issue and will take some on the ground inspection to determine the best route to take. Their number should be in your local phone book.  Here is a link to more information on one of these decay fungi.  http://www.forestry-dev.org/diseases/CTD/Group/Canker/canker6_e.html