Wiltshire Police said there had been an increase in the number of the patterns appearing in fields in the county.
A spokesman said creating a crop circle was criminal damage and an offence. Damage caused means a loss in revenue to the farmer and landowner.
Wiltshire remains one of the hotspots for the formations, which appear every summer in the English countryside.
Wheat farmer Tim Carson said his land at Alton Barnes near Marlborough was first used for a crop circle 27 years ago.
For a time he would charge visitors to see them.
He said: "At the time it was the first one that had ever occurred anywhere in the world. Little did we know we would get hundreds more after that.
"It was a one-off but the press seemed to go for it, and people just started turning up. Thousands of people came into that formation."
However, he is now trying to discourage crop circle enthusiasts using his land as it creates harvesting problems.
The farmer, who currently has a crop circle in one of his fields, estimates a loss of about Â£120,000 in lost or damaged crops.
Mr Carson said: "This is quite a small formation compared to some of the ones that we've had in the past.
"The wheat is completely flat on the floor now, it's unlikely we'll be able to get the combine low enough to harvest it."
Farmers have been urged to report crop circles made on their land to police after a recent spate of them.