Q. Is there still an impatiens blight? What can I do if I think I have infected plants?
There has indeed been a blight among impatiens plants in the New York area for a number of years. The culprit is a devilish form of downy mildew. Many nurseries will still not stock them because they are not able to guarantee that they will thrive and they do not want to risk spreading the disease. But, as you know, they are extremely popular annual plants so there are many places that continue to meet the demand.
If you suspect your impatiens have a disease, it would be wise to remove them from your garden. Here is an article from the New York Times that recounts the spread of the disease: http://www.nytimes.com/2013/04/18/garden/a-mold-devastates-impatiens.html
Many gardeners are substituting New Guinea impatiens, a "cousin" of the old faithful garden plant that is resistant to the blight.
Courtesy of NYBG Plant Information