Looking for a fiction book I read in the 1990s about plants that were genetically modified and somehow it got out and destroyed the crops. This was before we learned of GMO of today!
Is it either John Christopher/Samuel Youd's 'The Death Of Grass'
A new virus strain has infected rice crops in East Asia causing massive famine; the virus is also revealed to be found in the UK but because of its selectivity does not affect the country's agriculture. After the introduction of a new pesticide, developed in preference to breeding resistant crops, a new, mutated virus appears and infects the staple crops of West Asia and Europe such as wheat and barley—all of the grasses (thus the novel's title). It threatens a famine engulfing the whole of the Old World, while Australasia and the Americas attempt to impose rigorous quarantine to keep the virus out.
...or Clifford D. Simak's 'All Flesh Is Grass'?
A mysterious invisible barrier suddenly encloses a small, out-of-the-way American town. It's been put there by a galactic intelligence intent on imposing harmony and cooperation on the different peoples of the universe. But to the inhabitants, the barrier evokes stark terror.
Sounds more like the former to me, but you never know... and if it's neither, I'll be interested to see what it is!