Hi there. I don't know what you mean by 'mimosa plant fungus'. Can you upload some photos?

Not sure what you mean by 'mimosa' - that's a name commonly applied to more than one plant, i.e.,Albizia julbrissin, Mimosa pudica and a couple of others. Second, 'fungus' could mean several different things, i.e. rust, black spot, mildew, mushrooms, toadstools, bracket fungus.

Please supply more information or a good photograph.