Irritate at the plant (6)
I believe the answer is:
'irritate' is the definition.
(I know that irritate can be written as nettle)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for nettle that I've seen before include "Grasp it firmly and it will not sting" , "Provoke" , "Upset" , "Annoy; common weed" , "Sting or annoy with the plant" .)