SOLOTHURN, Switzerland — Before he mows the hay he feeds his dairy cows, Hansueli Wyss performs a new ritual: He scours the fields of his 65-acre farm amid the rolling hills of this farming region, dotted with steep-roofed homes like his 150-year-old farmhouse, for junk — empty bottles and soda or beer cans, hamburger cartons, and much else.

“It’s plastic bags, aluminum cans,” said Mr. Wyss, 50, who reared three children on the farm. “I make an effort to keep an eye on the cows, on the fields, but my machines shred this stuff in with the hay and the silage. That’s where the problem begins.”

Hard as it might be to believe, the orderly Swiss have a litter problem. Oddly, though, it is not in their towns and cities, where you might sooner stumble over a meteorite than a flattened Coke can or empty cigarette pack.

Out in the countryside here southwest of Basel, it is another story. So much litter is tossed out of cars that Swiss farmers have begun a campaign to fight it. They complain not just about the mess but about the danger the refuse poses to livestock.