Scales tend to be a small problem with most irises, but once established they will overtake the area/plant. Ants do not destroy them. Only when in their "soft" stage do any liquid sprays work to kill them. When in their hard shell stage they are impervious to the sprays. The danger of the sprays is that predatory wasps and ladybugs, which can destroy the scale, are also killed.
Recommendation from
http://www.herbs2000.com/flowe... is to destroy the plant infested with heavy amount of scale. At this stage of the season I would just cut off the affected foliage and put it in the trash, then watch the plant carefully. If only a small amount the scale can be manually crushed or swabbed with a cotton swab dipped in alcohol.
