Jim Mathison, head of Stroud Town Council’s Green Spaces Team, discovered the damage during maintenance work at the cemetery after returning from holiday.
The town council manages the cemetery. The old cemetery, which was attacked, is kept as a wildlife reserve.
Grass is kept long in the summer to encourage wildlife such as insects, reptiles and birds. Wildflowers, such as oxeye daisies, Scabious and valerian, are allowed to grow and bloom to encourage insects and bees.
“All the area that has been sprayed will now need to be reseeded,” said Mr Mathison. “We work hard to manage the cemetery as a wildlife reserve. Incidents such as this can cause great damage. It is also a criminal offence.
“We keep the grass long for a very good reason. At first I thought this was someone trying to clear a grave and the herbicide had drifted. But once we cut the grass we could see the extent of the damage.
“It would have taken someone some time to spray this much weed killer.”
The town council is planning to put up new notices at the cemetery explaining the work being done to encourage wildlife.