Notwithstanding an authorisation granted under Article 20 a Member State may be authorised to prohibit the use of the variety in all or in part of its territory or to lay down appropriate conditions for cultivating the variety in accordance, in cases provided for in paragraph (b), with the conditions for using the products resulting from such cultivation:

1. (a)

   where it is established that the cultivation of the variety could be harmful from the point of view of plant health to the cultivation of other varieties or species; or

2. (b)

   where it has valid reasons for considering that the variety presents a risk for human health or the environment.