Yep mum has it right, do they specify what paths you must have in your contract? How do they know that you wont keep them weed-free? A bit like little hitlers (to coin a phrase) going on here, and they are trying to bully you IMO. Dont give up yet , Tesco wont miss you, and have a good look at your contract. These old fashioned 'do it like we do' attitudes need to change