Growers can easily build their own nontoxic bait station for rodents, patterned after a system originally devised in California to control bubonic plague in chipmunks. 
Conservationist John Schuster offers the following plans and bait recipe:

Bait: Mix three parts of oats with one part plaster of Paris.

Station: Make a 24-inch–long “T” of four-inch–diameter PVC pipe. Seal off one end of the arms of the T and put a three-inch reducer on the other, putting a cap on the leg of the T for bait access. Bury the arms of the T in the ground, bringing the reducer end up to ground level for entry into the station. The small three-inch entrance of the sealed system keeps skunks and larger mammals from getting inside. Keep the system dry inside and use only when weather conditions are dry.

Directions: Place a cup of the bait in a small container, setting it inside the station.

Results: Ground squirrels or voles eat the oatmeal mix and return to their dens to die.

“Once they get a belly full of that, it’s curtains,” Schuster said. “I’m telling you, they have serious constipation issues.” Rodents will die without using poison or contaminating the food chain, he said. If raptors or other animals pick up a dead squirrel or vole, the congealed mass inside the rodent’s body is like bone and will be regurgitated.