Garden Pests and Diseases: Black spots and yellowing leaves on delphiniums, 1 by BobLI

BobLI wrote:
Howdy,

I have delphiniums that I started from seed outdoors in the fall, and brought inside for the winter. The plants are grown under vegetative CFL bulbs. About a week to two weeks ago, I noticed some of the lower leaves start to yellow, and wither. Shortly after that black spots appeared on the upper leaves. When I rub the tips of the leaves with my fingers, nothing comes off on my fingertips, and yet the black spots remain on the leaves.

Does anyone have any thoughts as to what the culprit may be? I feed the plants a diluted compost tea every two weeks.

Thanks,
Bob