On September 27, Georgia representative Rick Crawford (D-Cedartown) announced that he has switched to being a Republican. A few hours later, the Georgia Democratic Party state committee, which happened to be meeting anyway, voted to ask the Secretary of State to remove his name from the ballot. Courts in Alabama and Tennessee have permitted political parties to override the primaries, but apparently this idea has not yet been tested in Georgia.
The ballot already contains a Republican nominee, Trey Kelley. See this story. Thanks to Kyle Bennett for the link.