Figure 1. Corn plants exhibiting symptoms of rootless corn syndrome. As described in another article, corn plants produce two root systems. The primary root system is composed of roots that arise from the seed. These roots do not become large nor do they extend very deep into the soil. Their purpose is to nourish the young plant until the secondary root system becomes established. The secondary root system consists of many adventitious (nodal) roots that form at stem nodes both below and above the soil surface.
The transition between the plant's reliance on the primary root system to a fully functioning secondary root system is usually smooth with few problems. Unfortunately, weather and soil conditions can interfere with nodal root growth. All roots, including corn nodal roots, require moisture for growth. Roots will not grow into dry, hot soil. Roots extend through soil inside soil pores. Root development requires pore spaces large enough for root tips to enter, but not too large so that dry air touches the root tips rather the thin films of water that surround soil particles.
Because nodal roots are initiated on stem nodes about 3/4 of an inch below the soil surface, the microclimate in the top inch or so of soil is crucial in determining the fate of nodal roots. Dry soil, compacted soil, cloddy soil, or waterlogged soil can limit or even prevent the growth of nodal roots.
Figure 2. Corn plant with stunted nodal root growth typical of rootless corn syndrome. Soil conditions that limit nodal root growth can lead to what is often called "rootless corn syndrome". Corn plants are not truly rootless, because they usually possess a functioning primary root system (Figure 1). The rootless adjective refers to the severely reduced growth of nodal roots. The nodal roots actually initiate and even begin elongation. But, with unfavorable soil conditions the root growing points desiccate and root elongation ceases. The results are very short, stubby roots that often end in a blunt point (Figure 2). It should be noted that herbicide injury to roots is almost never the cause of what I've described as rootless corn syndrome.
With this syndrome, corn plants may appear normal through V4 to V6. But, as plant continue to grow; they begin to lodge because nodal roots had not formed properly. The primary root system is unable to anchor large seedlings. Unfortunately, little can be done to counteract the syndrome. Rain is the only effective solution to the problem. Using a cultivator to push soil around the plant base is not effective. Although stunted roots with desiccated growing points will not resume growth, wet soil will allow for growth on newly initiated nodal roots.