Allotments 4 All

New to the boards after a while 'lurking'.  Have a long neglected allotment on which the previous occupier appears to have grown lots and lots of rhubarb and blackberries.  Apparently he made a lot of wine.
Anyway I have a huge number of blackberries spikey things to remove.  Any helpful hints on timing and techniques?

Weedkiller and dig,dig dig!. Or the lawnmower, gets rid of them when they come up in grass!

Hi Hex,  nice of you to come out and stop lurking.
Lots of helpfull advice will soon be flying your way I'm sure, unfortunatley not from me, also a newbie of 3 weeks.
Bye for now