Answer: Based on your description it sounds like they suffer from an infection. Avoid overhead watering, do not overcrowd the plants, and be sure to clean up and remove all the plant debris in the fall to try to limit sources of reinfection. It can be helpful to rotate your plantings so that you are not replanting the impatiens in the same spot every year. Also, using good quality compost as a top dressing every season can help feed the soil and keep plants vigorous and healthy so they are better able to ward of diseases. Your local Penn State county extension should be able to give you a more specific diagnosis of the problem based on some over all and close up photos and/or samples of affected leaves/stems (enclose in a clear plastic bag and keep cool so they stay fresh). If a chemical control is needed they will be able to tell you what to use and how/when is best to apply for maximum results. Good luck with your impatiens this summer.
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