What plant names to capitlaize
 

I have a question about what plant names to capitalize. I am
identifying weeds and pests in lawns and i am using plant names in the
subject header. I already know that the genus name is capitalized, but
the species name is not. And the two are usually italicized.I f for
example i am using the name of a grass such as tall fescue, would it be
capitalized if not used at the beginning of the subject header since it
is just a common name? Hope i made sense.