Posted: 28/05/2012 at 18:00
The standard chemical treatment used to be Armillatox. However, since the manufacturers couldn't afford the high costs of testing etc. the product is now sold for cleaning greenhouses, paths etc. (A bit like Jeyes fluid, I suppose).
Where there is a large ornamental area to deal with, you can still used the product. www.armillatox.com will give the dilution rates.
I have used it successfully where my rhodos and azaleas were being munched. For pots I use Provado. I don't (fingers crossed) have a problem with edibles.