Blossom thinning of apples with Lime Sulfur has been normal in Washington State apple country for a long time and some brands of LS are now labeled for that purpose in other states like Pennsylvania, NC and VA.
I don’t believe the LS label mentions Fire Blight specifically, but the LS also helps control Fire Blight, however I have been told that it is easy thin too many blooms.
I used it mainly against pear blister mites. It was very effective.
But it has been banned in MA. Can’t order it on line. Companies will not ship to MA and many other states.
I hate the smell of Lime Sulfur and I was advised to carefully wash down my tractor and sprayer after using it because it could destroy the paint on my equipment. The fact that most versions are ORMI approved for organic use does not relax my concern over using it.
LS does not require a pesticide license in my state, but some states require a license so I’m not surprised it may not be available in MA. I believe at some point LS was used as a poison by some folks who wanted to commit suicide which must have created a lot of media attention and fallout.