It might be that. I think the more tender green plants could be weaker to it. I read somewhere that star-grass has issues, and excel always caused my Bacopa australis to melt (well, no proof but if I use it, it melts and if I stop, it grows back like crazy). M. umbrossum was not as susceptible, but did not like it either. Oddly, HC which is a relative of theirs (same family) likes excel. Go figure.