Lime sulphur should be at 1-3% on dormant trees not 10%. I don’t know if that was the cause of the problem or not though. Mixing with oil should not be a problem when dormant, I have done that many times.
Note that there were some bad freezes in your area this winter, that could have been the reason behind the flowers dying. Adding local expert @mamuang
Thank you very much. I will reduce the concentration next year. and check with wmang
sorry , Mamuang.
No need to apologize.
Your profile says you are in the Greater Boston, probably 6b. Still, many of us in New England lost stone fruit esp peaches, nectarines, plums when temp here went down to -7, -8 in early Feb.
If I were to guess, your fruit buds were killed then.
Were you sure that your fruit buds survived the Feb deep freeze?
I just sprayed dormant oil and lime sulfur at delayed dormant about two weeks ago. No damage to anything.
Peach and plum flower buds were on the trees but they were long dead.
Pears and apples are cold hardier and have survived the Feb freeze.
My first surround spray seems to have been well timed. No PC bites on any fruit that I can find. Apples and a few pears are pea sized or slightly under right now. This is my best year for apple blooms and pollination that I’ve had so far, I think some of it is secondary to more summer pruning. First McIntosh blooms on MM111. 
Goal is to get through this week unscathed. Not as simple as it sounds.
As @mamuang described, most peach and pear blooms were killed in earlier freezes. Reliance still has fruit, true to it’s name. A few on hale haven, none on redskin, none on loring, a few on Belle of Georgia, none on white lady, Babcock, or sauzee swirl. Black boy might have a couple. Already formulating some hardier grafting ideas for next year. 
@mamuang&@Rosdonald @scottfsmith . Thank you for helping me over coming the guilt feeling for losing my peaches flowering this spring. I am in Zone 6a. The peach trees are still struggling to leafing out at some part of lateral branches. I had heavy pruning this spring on peach to prepare new branch for next year.
Yes, I am sure my peach trees did survived from Feb deep freeze. My trees show bud and branch waking up early in March. same spray on new arrived peach trees from north NY state without hurt giving two or three flowing.
My peach trees showed buds, too. But those buds never developed. They just sat there fooling me. Then, leaves emerged but flowers did not. I pulled some buds, cut them open. Ovules were black/dead.
Apricot buds were so fried they fell off when I touch them. Peach flower buds stayed on but were dead from inside.
True, I did the same check as you.
Peach trees have no problem surviving zone 6 a. That is never an issue. It is the flower buds that can’t withstand subzero temp and/or yo-yo temp in the winter and early spring.
You’d better get rid of guilty feeling sooner than later. Growing stone fruit in zone6 a is a gambling. Sometimes you win, sometimes you lose. That’s about it,
How much Indal per Gal add to tank for brow rot prevention? I lost the record of it. Thank you in advance!
See the spray amounts guide:
I think it’s 1/3 tsp per gallon.
Thank you very much@scottfsmith!