Certified GKH Gardening Expert
Neem oil may also be effective, both as an organic fungicide and pesticide. These articles should help: https://www.gardeningknowhow.com/ornamental/shrubs/photinia/growing-red-tip-photinia.htm
There are a couple sprays that should help with this problem. One is called Banner Maxx, its cheaper generic is called Honor Guard. An earth friendly more organic fungicide would be one called Green Cure.