Although the early spring weather allowed for some quick progress on corn planting, that has not yet been reflected in emergence. With the cooler temperatures occurring over the past few weeks, emergence has been slow and uneven. As of April 21, 12 percent of the seeds had been planted statewide, with some districts (south central) reporting 27 percent of corn planted. However, emergence has only reached 6 percent statewide and 14 percent in south central Iowa as of May 5. We planted corn on April 16 outside of Ames and recorded a soil temperature of 73°F at 2 inches. But the cozy seedbed did not last long. By April 25 the soil temperature had dropped back to 55°F in the same field, and the corn had only just begun to germinate by May 4.
Cool temperatures are favorable for soilborne fungi to attack corn seeds. If seeds lie long enough in the soil without adequate temperatures for germination and emergence, eventually they will decay. A combination of cool weather and wet soil conditions is the best recipe for seed rot and seedling disease, but the good news is that there is not much saturated soil across the state. Soils rated as having surplus surface moisture rose from just 3 to 12 percent during the last weeks of April.
|Cool temperatures cause stress in corn seedlings.
On May 6, extension field specialists all had the same comments about corn emergence: "poor color, uneven, weak, struggling." The slow development is a result of cool temperatures. But the field specialists also reported that they were not seeing any major problems with stands and they felt the corn would be doing well once it warmed up. This would be a contrast to last year, when corn replanting reached record levels (approximately 1 million acres).
It is too soon to tell what will be the extent of replanting needs this year, but so far, problems seem to be scattered and with a little warmer weather we should see some great-looking corn stands.
This article originally appeared on pages 65-66 of the IC-488 (8) -- May 13, 2002 issue.