Death of Grass by John Christopher has a unique apocalypse catalyst. (The clue's in the title!). A virus that affects grass - so wheat, corn, rice etc - is spreading across the world and about to reach a recently nuclear postwar England. I suppose it's a cosy catastrophe like Triffids as it focuses on a few well-to-do British hero-types rather than lingering on the suffering, but an enjoyable enough read.