Black Spots on foliage of Lilium orientalis
I live in Seattle, recently my oriental lily foliage started to develop some black spotting. I fertilize it about once a week with 9-18-9 water soluble liquid plant food. The pH is about 6.5. Any idea what it could be?
I suspect a fungal disease, but which one I'm not sure; there are multiple possibilities.
What can you do? Sanitation, prune out and dispose of infected leaves, avoid overhead watering that can spread the spores, address soil fertility and water management to keep the plants as healthy as possible to resist disease.
A systemic fungicide from your garden center can be considered.
The following link has the best description of the various possibilities that I could find.