Corn planting is more than two weeks behind schedule in Minnesota, and a forecast of more midweek rain is stoking fears that yields will be squeezed by late planting for the second straight year.

"We just haven't had a decent window to do much of anything out in the fields yet," said Liz Stahl, a crop educator at the University of Minnesota Extension in Worthington. "Too cool and too wet. Too wet is the biggest problem."

Only 6% of the Minnesota corn crop was planted as of Monday, the U.S. Department of Agriculture said. That's 17 days behind the five-year average, and a day behind where farmers were a year ago.

Iowa, Illinois and Indiana, where corn planting happens earlier in the spring thanks to the warmer weather, are even further behind schedule, according to the USDA's Crop Progress and Condition report released Monday.

Delayed planting affects the harvest because it gives the corn less time to develop the leaves it uses to convert the sun's energy into big ears full of kernels in the heat of late summer. Corn that reaches maturity later also may not dry out as well in the fields before harvest.

Dry, breezy weather over the weekend and early this week will help, but more rain is in the forecast in Minnesota.

"Starting Wednesday it looks like we're going to have a low-pressure system come through with pretty good rain amounts," said Chris O'Brien, a meteorologist with the National Weather Service in the Twin Cities.

While the Twin Cities is expected to only get a half-inch of rain or so, the forecast for the southern tier of the state, firmly within the American Corn Belt, is for 2 inches of rain.

Intermittent good weather isn't enough, because the soil doesn't have time to dry, said Jeff Coulter, an agronomist at the University of Minnesota Extension.

"If we get some rain and then we get good weather the next day and then we get more rain it doesn't really help," Coulter said.

Last year, farmers were able to catch up within two weeks of today's date, thanks to sustained good weather.

Farmers still have wiggle room, Stahl said. It's been too cool in much of the state to plant corn so far anyway, and as long as farmers can get in the fields by mid-May, their yields should be pretty close to normal, assuming everything goes well the rest of the growing season.

"When people do get nervous and push it hard, if you plant when conditions are too wet, that can create issues," Stahl said.

Driving a tractor on wet fields compacts the dirt, making it more difficult for roots to penetrate the soil.

"If we could have some nice, dry weather, people could get the corn in in short order," Stahl said.

But if the rain falls as forecast on Wednesday and the weather doesn't improve, farmers will be forced into hard choices, perhaps even having to switch to soybeans.

"If we're unable to catch up by the end of next week, our outlook may be declining significantly," Coulter said.