Bermuda grass (also called Devigrass, wiregrass) is an annual, fine textured "creeping grass" that grows and spreads rapidly via rhizomes and stolons during warm summer months.
Due to its rapid and sometimes widespread growth during warm months, Bermuda can quickly take over cool-season grasses while dormant. Herbicides are usually not as effective as simply hand-picking these weeds before they grow out of control.
To help prevent this, you can apply a pre-emergence just prior to its growing season (usually spring time) to prevent the seeds from germinating. However, the other extreme is to apply fluazifopbutyl or glyphosate to kill all of the grass, then reseed over it. This is only suggested if you plan on replanting or renovating your lawn afterwards.