The edges of the petals were brown. The symptoms are more likely to occur on light colored roses. There are two possible causes listed in the textbooks. The second possible cause is an invasion of thrips. To check this, I opened the blossom and examined the petal base areas.
Thrips do their damage by sucking juices from the petals.
The trails for their successive penetrations shows a rasping pattern. It appeared reasonable with all the hot dry weather we have been having. The thing that bothered me a bit with this conclusion was that not all opening blooms had thrips in evidence, Also, I noted that a week later many of the blooms opened up normally with no sign of the balling, browning phenomena. This led me to take samples of the affected blooms and those not affected to Ethyl Dutky at the University of Maryland. When I noted that the foliage appeared to be in good condition, it was pointed out that the blossoms are more sensitive to heat damage.