use

[navi tasan]

Is this sentence correct:
1-They used worms to eat the weeds.

It seems weird to me. They do get rid of the weeds, but the worms are the ones who eat the weeds, not they.
(They use forks to eat their lunch)

[Tdol]

It's fine to me- the difference between your 'fork' example and this doesn't affect the logic for me because in each case it's clear who eats what.