Interesting......as I replace red tips with cleyera's, Just as I replace common hybrid tea and grandiflora roses with knockout varieties.
This disease is supposed to be resistant in these two species of plant but nothing is to say it will not occur. My knockout roses sustained black spot and one plant exuded what appeared as the common mosaic virus. We are under the impression that these hybrids are immune to an extent.
Excessive moisture, humidity, foliar watering, and other host plant infections will spread this disease. Cool episodes with sudden changes in temperature is going to prolong this disease.
The best thing to do is definitely diagnose this disease from state testing. The guessing game isn't going to be accurate. Send in green leaf tissue along with stems. This way, the agent can diagnose the problem using a microscope. Many of us has seen diseases that appear to be similar, but no one is completely accurate without seeing the infection firsthand.