A cooler than normal May has slowed the development of corn that was planted in late April or early May. Much of the state's crop has been planted only in the last several weeks and is just now emerging or is at very young growth stages. The bottom line is that a lot of corn in Indiana is just now getting around to developing its permanent (nodal) root system. Weather and soil conditions over the next several weeks will greatly determine the degree of success in establishing corn root systems.
Two factors come to mind that can influence corn root development in 1995. One is the widespread soil compaction that exists across the state this year due to fields being worked wet or planted wet. The other factor is the potential for rapid drying of the upper soil surface in early to mid-June that can stunt the growth and development of the corn plant's root system.
Soil Compaction. Obviously, soil compaction can restrict root growth and prevent the development of a deeply-rooted crop. Root development in compacted fields that continue to receive soaking rains over the next several weeks will suffer because such fields will likely remain saturated for longer periods of time. Root development in compacted fields subjected to hot, dry conditions over the next several weeks will suffer if the rooting is restricted to the upper soil surface layers. A longer-term switch to hot, dry conditions will greatly hamper corn growth and development in these fields compared to fields where soil compaction is less (remember the drought of 1991?).
Those compacted fields that receive sidedress applications of nitrogen fertilizer will benefit from the injection knives running through the middles of the rows. Row cultivation will likely not relieve much of the compaction, since it is rather difficult to cultivate deeply enough to break up compacted soil without greatly disturbing the corn root system.
Rapid Drying of the Upper Soil Surface. Warmer than normal temperatures, coupled with strong winds, can dry the upper inch or more of soil very quickly. Root 'buds' from any given stalk node that begin to elongate in dry soil or in soil cracks will quickly cease growth due to insufficient soil moisture. If the soil remains dry long enough, the root tips may dessicate and die.
If dry surface soil and/or hot, dry weather prevail, several sets of nodal roots may fail to form, giving rise to the rootless corn phenomenon. Affected plants are forced to depend on the seminal roots, seed reserves, and mesocotyl for nourishment, when normally this lifeline has already taken a backseat to the nodal root system.
In addition to the nutrient stress imposed on the plants by not having an adequate permanent root system, the rootless phenomenon can eventually lead to the floppy corn syndrome. These plants are technically not root-lodged, they are simply broken over at the base of the stem near the crown area.
The permanent roots will appear stubbed off but not eaten. The tips of the roots will be dry and shriveled. These symptoms are unlike any associated with herbicide injury or insect feeding. Because several sets of roots may not have formed below-ground, the crown may "appear" to be at or above the surface.
The important thing to remember is that roots will not develop in dry soil. They will not grow toward moisture. If roots are already in moist soil, however, they may proliferate rapidly enough and appear to 'follow' moisture down as the soil dries. Row cultivation may throw enough moist soil around the stalks of the plants to encourage root development and provide some structural support. However, the ultimate answer to the problem is a soaking rain before the whole field has 'flopped'.