The real problem in this case is probably aphids, tiny insects which are feeding on your rose plants and excreting a sweet substance called “honeydew.” Ants only show interest in roses when there is enough honeydew present to attract them. Spraying with a horticultural oil or an insecticidal soap to control the aphids will generally eliminate the ant problem. 

Additional Resource: 

http://edis.ifas.ufl.edu/MG002

http://edis.ifas.ufl.edu/pdffiles/EP/EP33900.pdf