Has the weather been really hot? This will shrink bloom size.

Are you watering enough? This will shrink bloom size, too.

Is there less foliage on the plants than in the past, due to disease? This will reduce vigor.

What do you fertilize the plants with? Roses need fertilizer at least once a year.

I think its the weather because its old and new plants and it did begin after this heat wave has hit MD. Im watering but i dont water allover i only get up close and spray near the crown im so afraid to cause blackspot and mildew. If they get sun by 11am and I soak them from watering around 10 will that cause disease problems or just help them?

Don't worry about it.
You say you're having a heatwave -- that's very normal for roses in hot weather. It's their way of conserving water.

When the temperatures drop, the blooms will return to the size you're used to.

Jeri

As long as the roses have plenty of time to dry off before it cools off at night, I wouldn't worry about watering causing blackspot problems.

Kate