Sounds like you live in an area where the humidity is high. This is a problem with Impatiens and Roses.
Only advice I can give you is to make sure your impatiens aren't planted in direct sun. They do much better in shade/part sun. Also, they don't like a lot of water, so over watering will cause the leaves to turn yellow. Also, try not to get the leaves wet when watering.That can cause black spot.
Planting in an area where they get plenty of air circulation will help also.
Only advice I can give you is to make sure your impatiens aren't planted in direct sun. They do much better in shade/part sun. Also, they don't like a lot of water, so over watering will cause the leaves to turn yellow. Also, try not to get the leaves wet when watering.That can cause black spot.
Planting in an area where they get plenty of air circulation will help also.