Phyllosticta leaf spot is identified on impatiens as spots that are tan and have concentric rings within them, indicating that small spots grew and grew. At the center of the spots, you may see (with a hand lens) a scattering of round dark bodies that are spore cases (pycnidia) for the fungus. This disease is found on New Guinea impatiens and Impatiens wallerana. Very little is known about this disease on impatiens, but restricting the leaf wetness periods and using standard anti-leaf spot fungicides should be effective for control, when coupled with roguing out the plants obviously diseased. Most leaf spot-countering fungicides will help against Phyllosticta, including the thiophanate-methyls, chlorothalonil, iprodione and coppers. Keeping foliage dry is an important control tactic.
Information from "What Can Go Wrong With Impatiens (Impatiens wallerana) Leaves" by Margery Daughtrey, Cornell University
http://njaes.rutgers.edu/pubs/fipmnotes/2007/fipmnotes17-05.pdf
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