Japanese Hollies have a white powdery substance
My 10 yr old Japanese hollies have a white powdery substance on the stems and branches. The leaves are unaffected. One of the hollies is especially bad looking where the leaves and branches are brown and dead. I did not notice the fungus type stuff as you have to look directly into the bush and spread the branches to see it. I never would have noticed anything until the one plant began to turn brown in sections.
Certified GKH Gardening Expert
Powdery mildew is caused by fungus that attack Holly leaves, sometimes covering them entirely with a thin white powdery coating. For more information, here is an article that you may find helpful: https://www.gardeningknowhow.com/nonorganic/get-the-cure-for-powdery-mildew.htm