Over the last month there have been a number of reports of corn plants "flopping in the wind" due to lack of nodal root development. |
There have been many theories as to the cause of these "floppy" corn plants. One theory floating around the state is that early preplant or preemergence applications of 2,4-D or other plant growth regulator herbicides have caused the mesocotyl to rapidly elongate above the soil surface, therefore not allowing the nodal roots to form. Even though this may sound like a valid theory, more times than not floppy corn is generally not caused by herbicide applications. In fact, typical injury symptoms from plant growth regulator herbicides applied preemergence include twisting of the mesocotyl,
leaf wrapping, and sometimes leafing out underground. What we have seen on corn plants sent to the Plant Clinic are symptoms consistent with what is known as "rootless corn syndrome."
Rootless corn usually develops when the nodal roots initiate growth at or near the soil surface. Early this season, much of the corn crop was planted in dry, loose, fluffy soil. When the weather turned wet and cold, the rains compressed the soil, causing the nodal roots to form closer to the soil surface than normal. This, along with fluctuating environmental conditions that have occurred through most of the growing season, has caused the nodal roots to cease normal growth. If nodal roots fail to form,
affected corn plants depend on the seminal roots and mesocotyl for nourishment, and the seminal roots become the primary anchor for the corn plant. Without the nodal roots, the corn plants do not have much of an "anchor" to help them stay upright. This is when we see floppy corn or corn that is easily blown over by the wind. Another cause of rootless corn is shallow-planted corn, which places the crown close to the soil surface, causing nodal root development near the soil surface rather than the usual inch depth.
Even though it's probably too late in the season to do much for plants in this situation, what can be done for next year? It's always important to plant corn deep enough, and if rootless corn syndrome begins to develop, row cultivation may encourage root development when moist soil is thrown around the base of the plant.--Christy Sprague and Aaron Hager