They use a "selective" weedkiller called Grazon 90 although there are other ones. You should not attempt to buy or use this chemical yourself as you need to have a spraying certificate and properly store the product. Too many ametuers cos too many problems. You ought to go and have a word with either a local farmer or the head gardener of a local national trust garden (or similar) about asking them to supply the required chemical and equiptment. Then either pay someone to do it or ask them to do it for some beer money.
I've been a head gardener for over 20 yrs and never minded locals asking favours.
Hope this advice is well recieved.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!