This name is a synonym of Erigeron thunbergii A.Gray.
The record derives from TICA
(data supplied on 2012-02-11)
which reports it as a synonym (record 35CD8D04-2E02-4B4F-B604-E456FDB6D2FD).
This name record (from TICA) was not included in version 1 of The Plant List. It is possible the same name was included from a different data source, to check this you can search for Aster dubius in version 1 of The Plant List.