If ever you feel that your day is too cheerful, go read John Christopher's The Death Of Grass; it'll sort you right out.

http://www.goodreads.com/book/show/941731.The_Death_of_Grass

In it, a rice virus mutates and wipes out all grass crops in Asia and Europe --- rice, wheat, barley, oats, you name it.

tl:dr: it doesn't go well.