Mock orange sores
This plant is called a Hardy Orange (Poncirus trifoliate). It is from a different family than a mock orange is. I looked it up in several books and they all said it was free from insects and diseases even though yours looks like it has a canker. Usually treatment of cankers involves cutting a few inches below the canker and then using fungicides on the plant. That being said this is not a common plant in New England so I am not familiar with diseases that this species might be susceptible to. You may want to submit a sample of the canker area to the UConn Plant Diagnostic Lab where the plant pathologist can take a look at it. If you are interested in doing so, there is information on this website :www.ladybug.uconn.edu. about how to submit a sample.