So, i use no pesticides on my yard, but i worry that whille my tortoise is grazing she will eat something she shouldn't. Is this a possibilty, or will she not eat anything harmful on her own?
It is a valid concern, but after 42 years in a garden where I do not pull out poisonous plants, I have failed to kill Joe. They may take a bite of the bad stuff, but generally don't bother or decide it tastes horrible.
In my view, if he's being kept in a small enclosure, take care with what's in there too.
If he's roaming over a large yard with plenty of choice, don't worry.