A Delafield farmer says rising diesel prices are cutting into his bottom line and could impact grocery store prices for Milwaukee-area families and beyond.Jim Renn and his family farm about 800 acres of corn, soybeans, wheat and hay in addition to raising 200 beef cattle. Almost every aspect of running his operation depends on diesel.Our biggest tractor is 300 horsepower, and that fuel tank in there is about 125 gallons, Renn said. If you think …