Rain-delayed planting is no reason to switch from corn to soybeans or to switch to an early-maturing corn variety, says Bill Wiebold, a University of Missouri (MU) Extension agronomist. Yields usually begin to drop on corn planted after May 10 in central and northern Missouri. Continued rains and cool soil temperatures kept farmers from planting cornfields at usual times in mid-April.

"I would stick with corn through the end of May," says Wiebold, corn and soybean specialist. "With the high price of corn, there is financial incentive to stick with corn even with some yield loss."

Growers have to make individual decisions for their farms, Wiebold said during a weekly teleconference with MU Extension regional agronomists. "Even if you incur a 5% yield loss after May 10, it doesn't make economic sense to try to find soybean seed and make the switch."

Rains coming every other day haven't made planting decisions simple for crop farmers this year, Wiebold says. He cautions against rushing into the field before the ground is ready to work. Planting in wet fields can cause soil compaction and form clods that will hamper crop growth.

"Planting when soils are wet can compact the planter slot sidewalls. That compaction increases root damage and restricts where roots can grow," Wiebold says. "The corn may come up and look fine until dry weather hits. Then there won't be enough roots to supply water to the plant.

"Rain is our major concern now. Soil temperatures, which should be above 55° at the 2-in. depth, are safe for planting now. If they are not warm enough, they will be in a few days."

Switching to an early maturing variety almost assures yield loss. "Those early varieties are shorter and have less yield potential," he says. "An early variety might offer some advantage in reduced drying time at harvest, but that depends on the fall season."

Anyone switching from a 110-day hybrid to a 100-day hybrid should increase seeding rates by up to 4,000 seeds/acre to offset potential loss.

Delayed planting increases the risk from drought damage at the time of pollination. The later a corn plant matures, the higher the chance of pollen drop coming in hot, dry weather, which reduces kernel set on the cob.

In four years of planting-date studies at the MU Bradford Farm in Columbia, Wiebold found that corn yields begin to drop after the first week of May. By May 20, yields dropped an average of 16% compared with the earliest planting date over the four periods. By June 4, yields dropped 24%.

"So much depends on the weather in late June," Wiebold says. "We've had late plantings when rain and cooler temperatures occurred at pollination. Excellent yields resulted in those years."

With normal rainfall or irrigation, yield loss is minimal through at least mid-May planting dates.

Corn seed should be planted between 1.5 and 2 in. deep in the soil, Wiebold says. That allows for good root development, which helps later in a dry season. "In general, Missouri farmers plant too shallow," he adds. "For now, wetness is our problem. We need a week of good drying weather."