Every variety reacts differently so what ever it is could effect some and not all of them. Have you had really lousy cold weather like I've had? Could it be freeze damage? Or a combo of freeze and fertilizer burn? I've noticed that some of the leaves on mine that got frost bit look sort of silvery in color.

Same here---I thought everything was fine, but that's how the frost damage looked on our roses. Sort of silvery or white, then it turned crispy and brown.

thanks that has to be the Answer. we had temps down to 28 last month