Lettuce crops regularly denuded (3)
I believe the answer is:
cos
'lettuce' is the definition.
(cos is a kind of lettuce)
'crops regularly denuded' is the wordplay.
'regularly denuded' indicates alternate letters (letters removed at regular intervals).
The alternating letters of 'crops' are 'COS'.
(Other definitions for cos that I've seen before include "Variety of lettuce" , "foreign island" , "vegetable?" , "holiday destination" , "Senior officers" .)