If you apply a preemergent herbicide like Dimension, Halts, or Stonewall, it will prevent the annual rye from germinating. Also, don't water your lawn, and if some of it does germinate just use Round-Up on it when your Bermuda is completely dormant.

And for future reference, if your bermuda was thinning, there was a problem.

Bad cultural practices, insects, shade, deficiencies in the soil......Something was off.

Agree with Timeco. IMHO let it go for now, wait until the Bermuda is fully dormant, then hit it with RU as it is the least expensive and most effective option.

Now what you need to concentrate on is why is your grass thinning out. Without pictures I would guess shade or watering issues. But you need to get a handle on the cause so you can address it come next spring.

You don't say where you live and like the others opined, bermuda requires full sun to thrive. I have St. Augustine and live in Zone 8 in the Dallas area. I overseed my lawn with annual rye because I do like the green during dormant months and don't mind mowing. The early spring heat wilts the rye away pretty quickly. As far as Round-Up is concerned, be careful of root zones of trees and shrubs as it is an equal opportunity killer

If you are going to use a pre-emerge herbicide to control the emerging ryegrass seedlings, you better do it no later than this coming Saturday, which will be 6 days after seeding. Once the seeds germinate, most every pre-emerge herbicide will be ineffective. And I'm not completely sold on the claim of post-emerge control by Dimension herbicide prior to the 3 leaf stage.

Reseeding bermuda is not really done in the spring either. You will see a lot of advertising and see giant bags of bermuda seed starting in February but resist the urge. Bermuda seed takes best when the soil is very hot...as in July.

What kind of bermuda do you have now? If you have a sodded variety I would suggest you do not seed it under any circumstances. Seeded and sodded varieties are like two different plants. If you mix them, it will always look weedy.

I would have been tempted to take a 2x4 to my gardener if he had overseeded my lawn. That practice can be so debillitating to the permanent grass. Grrrrrr.

But, I'd probably not use a preemerge on my lawn at this point.