See:
Greenhouse Plants, Ornamental - Impatiens Necrotic Spot
Symptoms Pale green, circular, elliptical, or irregular areas that may become surrounded by chlorotic rings occur on leaves. On some leaves, numerous concentric rings varying in size occur. Chlorotic rings surrounding green centers may also be seen. Some leaves may show green or chlorotic banding of veins in large lemon-yellow blotches that may or may not have rings. In advanced stages of the disease, black rings varying in size surround chlorotic tissue which eventually becomes black on the lower leaves. Black patches spread on most of the lobes on the leaves, and petioles, and veins become necrotic. The lower leaves turn brown and dry with the blackened areas still visible.
Reference Wegulo, S.N. 2017. Diseases of Delphinium. In McGovern, R.J. and Elmer, W.H. (eds.) Handbook of Florists' Crops Diseases. Springer Int.