Crataegus -member of Hawthorn family

Q:  My neighbors have a thorny tree growing out of their pear tree.  It is growing quite large and we want to know if it is a wild pear or plum.  

A:   The specimen you brought to the office appears to be one of the hawthorns, Crataegus.  However, it is not the same variety of Indian Hawthorn most of us are accustomed to seeing in our landscapes. This plant could possibly overtake the pear tree and choke it out by girdling the trunk of the pear tree.  It would be best to remove as much of it as possible.  Cut it down as close to the root as possible, be careful not to cut into the bark of the pear tree.  An herbicide such as glyphosate (Round-up) should be painted on the stump immediately to discourage suckers from forming.  The flowers are probably similar to the pear flowers and therefore it has gone undetected for a long time.