In better-watered areas of Illinois where the corn crop is well established, the return of warm temperatures has caused very rapid growth. Corn planted in central Illinois in mid-March and not damaged by frost has accumulated about 900 growing degree days (GDD) by now and thus, has reached stage V9 or V10, the point at which stem elongation accelerates. Such fields will likely show tassels by mid-June. Corn planted in early April has accumulated about 650 GDD and is at V7. Corn planted in mid-April is at V5, having accumulated approximately 520 GDD.
Though the crop is in good condition in most areas, the dry weather pattern is causing some concern. Water use accelerates as corn reaches V7-V8, but it is still only about an inch per week. Dry surface soils have meant low evaporation rates, so most water is moving out through plants, which is an efficient way to use water. In most areas, plants are still growing well by extracting water from the soil, and the drying of surface soils is encouraging deeper root growth.
"In deeper soils that can provide 8 to 10 inches of water to a crop, there should be enough water to keep the crop growing well into June," said Nafziger. "At some point, of course, we will need rain to keep the crop growing up to its potential."
While the state's corn crop is nearly all planted and much of the crop is growing well, there are reports of "floppy" corn plants in western and northwestern Illinois and into southeastern Iowa. "Given the better-than-average planting conditions this year, this was not a problem that we expected to see," said University of Illinois crop sciences professor Emerson Nafziger.
"It's an easy problem to spot," said Nafziger. Plants develop using water provided by the seminal (seed) root system up to the 3- to 5-leaf stage, after which the nodal roots -- those that develop from the base of the stalk -- take over and become the main root system for the rest of the season. If the nodal root system fails to develop, the plant become wobbly and may fall over; hence the name "floppy" corn. This problem has also been called "rootless" corn due to the absence of nodal roots.
This year, the problem appears to be most common in corn that was planted in the last week of April and that is now at or just past the V3 stage. It has been observed in both no-till and tilled fields, though it is probably more common in no-till fields. This is because the no-till planting furrow can act as a barrier to nodal root growth.
Another source of difficulty for nodal roots is what has been dubbed the "high-crown syndrome" (HCS). This is a relatively rare phenomenon in which the base of the stem (the crown) ends up positioned at or very near the soil surface instead of at its normal placement about three-fourths of an inch deep in the soil. As a result, the plant ends up perched atop the soil. Because nodal roots of such plants emerge above the soil surface, they often have great difficulty penetrating the soil, especially under dry conditions.