Thank you for the question. Your impatients may be infected with impatients downy mildew, a fungal disease that is a problem in nursery and landscape plants in Minnesota. All varieties of Impatiens walleriana are susceptible, including hybrids with I. walleriana in their background. The disease may have become established in your garden last year, possibly transmitted through infected nursery stock or through the wind and water from infected plants nearby. Once a plant is infected, it can't be cured and the spores can survive 8-10 years in the soil, unaffected by winter cold. Your plants this year contracted the disease from the fungus in the soil or were infected when you bought them.
From now on, choose different shade plants like coleus, begonias, caladium, or New Guinea Impatiens which are highly resistant to the disease. To learn more about the disease and what to do now, read this University of Minnesota publication about impatiens downy mildew in the landscape: http://www.extension.umn.edu/garden/yard-garden/flowers/managing-impatiens-downy-mildew-in-landscape/
Thank you for contacting Extension.