Never dealt with that. Not sure soap would do the job. I'd think using white vinegar would kill the mold, but idk what acidity level would kill the leaves. Vinegar, hydrogen peroxide and rubbing alcohol kill mold. Idk if citric acid might work. And there's different levels of alcohols, too. That's a tough one. I'd research and if I couldn't find any info: I'd get 3 spray bottles and test 3 areas. Have seen entire crops lost simply due to inaction. As far as plants go, you can always replant/replace. Not sure? Why not experiment! Least you tried if it goes poorly. Good luck with your lime tree.