From the City of Great Bend...
With spring approaching, you may notice Great Bend city crews out spraying chemical at both cemeteries. The city does a full cover of all of the grounds in both the spring and fall with a pre-emergent. This helps prevent unwanted early season weeds and grasses from growing.
This is the one chemical that leaves a white residue. This might be noticed on darker stones more than on lighter stones as seen in the picture. However, this will not stain any of the headstones. In fact, it rinses off quite easily with the next rain.