What is this and will it harm my tree?
This appears to be ash flower galls. I excerpted from Dr. john Ball's pest alert. They will not harm your tree. Read on: Ash flower galls really stand out at this time of year. The dark gray lumpy growths are hanging from many ash trees. The “growths” are the male flowers that been infested with the ash flower gall mite (Eriophyes fraxinvorus). This mite spends the winter under the buds and moves out to the twigs as the male flowers begin to form. The mites lay their eggs in the developing flowers and once hatched the feeding activity by the nymphs causes the galls to form. There are several generations per year. The reason we see so many of these galls on 5 ash is that ash trees are dioecious, meaning it produces either male or female flower. Since no one likes seeds, almost all the ash cultivars we have planted are males so lots of food for this mite. The galls do not harm the tree and they eventually fall off, usually within a year or two, though new ones will form every spring.