Some friends of mine grew Impatiens walleriana (the ones affected by Downy Mildew) last year and they were fine, but its down to luck. Even if the plants you buy are healthy, there's nothing to stop wind blown spores of the fungus from attacking your plants, and still no treatment either. Most people now buy the newer strains of New Guinea hybrid Impatiens.

Thanks bamboo.Won't risk it then.