I'm told that the pollen falling from fields of rape is not, in fact, a cause of hayfever, as the pollen is large and heavy and falls to the ground rather than getting wind-borne. It certainly smells very unpleasant to me, and I'm with Michael in thinking that it adds a garishness to the subtle English countryside colours. The worst offenders, as far as hayfever is concerned, are tree pollens. Whether rape activates allergies other than hayfever, I don't know.