[pharnorth]

Ive found a small harrow pulled by the quad, or anything else for that matter is great at decimating nettles.

[landroverroy]

 I presume you know Tim that goats, and presumably alpacas as well, love nettles once they've wilted. So if you give them access to the field once you've cut the nettles, they'll probably clean them up for you.
In fact at the moment my sheep are eating nettles in situ. It's been so dry here for the last week with the constant wind that the nettles are actually wilting in the ground and the sheep are loving them.
 Also, if you  roll nettles, the weight of the roller breaks up the fine spines that do the stinging and again stock will eat them in situ.

[Rupert the bear]

cut and dry them , goat snacks