I am a big fan of post apocolypse and alternative future fiction, and as this is a somewhat different type of disaster, I pounced on it with eager anticipation. The plot has been covered quite well by other writers here - death to all forms of grass and the chaos that ensues, so I won't add to this in any detail.
What I will voice is my disappointment in the book. What I like about this genre of fiction is that it tends to show people surviving under the worst conditions that can be thrown at them, and to a degree this is no different. However, what we do have in this story is a group of essentially decent people descending into barbarism, and whereas this is in all probability entirely what would happen, it doesn't necessarily make for an entertaining read. My preference is for the characters to step up to the unthinkable challenges and become better people in themselves.
Added to a relatively weak plot line, these unpleasant characters make for a disappointing novel. It is an interesting enough book, for its rarity and unusual take on the "end of the world as we know it", but it's definitely not among the best.