Agronomist: Don’t panic over plant delays

Even though agronomy publications in the 1970s say corn should be planted no later than May 7 to assure full yields, that’s not the case in 2013.

Mark Johnson, an Iowa State University Extension field agronomist, told 28 producers and crop consultants on Wednesday at the Webster County ISU Extension office that corn hybrids can still reach a 95 percent yield if planted by May 18, and can yield reasonably well if planted later this month.

Although more rain was forecast for central Iowa on Wednesday and today, Johnson said the outlook was good for fair weather for the next week, and he is confident that farmers can get seed in the ground for a good yield without switching maturities.

In a nutshell, Johnson’s hour-long presentation told farmers:

Don’t panic.

Don’t work in wet fields.

Don’t switch hybrids.

Use the least amount of tillage as possible.

Test fields for nitrate availability in topsoil, because 2012’s carryover and fall-applied manure may have leached away with March and April rains.

Planting dates

Johnson said corn planted between April 15 to May 18 has a yield potential window of 95 to 100 percent, depending on soil conditions.

“Early planting and late planting,” Johnson said, “does not guarantee yields.”

He said soil moisture and temperature have more impact on early corn emergence and plant health than the planting date.

Soil temperature charts showed that Webster County was at 51 degrees on May 1, but slipped to 37 degrees by May 3 and didn’t get back over 50 degrees until Monday when it measured 53 degrees. About 5 to 8 percent of Webster County’s corn was planted before the May 1 snow storm that blanketed the county in 8 to 9 inches of wet snow. Northern tier counties got up to 13 inches.

According to Johnson, what corn was planted before May 1 needs to be scouted continuously from emergence to V1 stage (with one developed leaf), to determine if a field needs to be replanted. If soil conditions were too cold for seeds, he said, it will adversely affect emergence and plant health.

Johnson has inspected a few fields and found the young plants appeared to be in good shape.

However, he said, if a window opens for planting, he’d get seeds into unplanted fields before pulling the trigger for replanting.

Gene Frueh, of Barnum, said the advice was welcome news. He has a corn-soybean rotation and had done no field work as of Wednesday.

Johnson’s call to be patient, Frueh said, was confirmation that he had made the right decision.

Avoid wet soils

Johnson wants farmers to be patient and check soil conditions before planting.

“Many times, people get anxious and many get into the field one day too soon,” he said.

He advised checking soil moisture at planting depth and at tillage depth.

“If the soil forms in a ball and tossed in the air, it’s too wet if it doesn’t break up.”

Tilling or planting in soils too wet, he said, “will create what we call a smear layer, which will be a problem for roots to penetrate.

“I recommend on getting by with as little tillage as you can,” Johnson said.

Switching hybrids

Johnson said some farmers are considering switching to a shorter maturity hybrid due to delayed planting.

“It’s too early to switch,” Johnson said. “Hybrids, if planted late, will shorten the time from planting to silking, while lengthening the days from silking to black layer” or full maturity to allow for more grain filling.

He said days to silking are shortened more than days are lengthened to reach physiological maturity.

“Don’t switch until the end of May,” he advised.


Tile line monitors are showing excessive rates of nitrate leaching from fields within the Boone and Raccoon watersheds, according to Johnson.

This is due to the constant March and April rains. Much of the nitrates are from the 2012 carryover from the drought and fall-applied manure.

Johnson said the dry 2012 fall left nitrate in the soil. In addition, fall-applied manure underwent extensive change to nitrate because the ground remained warm until late December.

He expects that much of the nitrate being monitored from tile lines are from these sources.

However, he also expects that any nitrogen applied after soils cooled is still present, so he recommends sampling soil for nitrogen composition. Farmers not intending to sample should consider limiting nitrogen applications to normal levels, he said.

Concerning soybeans, Johnson said there is still plenty of time for planting them. May 20 is still considered fairly early.

When asked if rootworms will have hatched and starved before this year’s corn is planted, Johnson was doubtful.

“They operate on heat units (just like corn),” he said. “I don’t expect them to not be a problem.”

Johnson’s presentation was also viewed remotely in Pocahontas, Cerro Gordo, Calhoun, Hamilton, Humboldt and Wright counties.

Johnson is based out of Ankeny, serving nine central Iowa counties. He is replacing long-time ISU field agronomist John Holmes, who is retiring at the end of May.