No Blade of Grass(1970)

The creeping terror drifted towards them stamping out all civilization in its eerie path!

A strange new virus has appeared, which only attacks strains of grasses such as wheat and rice, and the world is descending into famine and chaos. Architect John, along with his family and friends, is making his way from London to his brother's farm in northern England where there will hopefully be food and safety for all of them.