Following last week’s storms I received several reports of “rootless” and “floppy corn”. The problem was evident in several fields at the OSU Western Agricultural Research Farm at S. Charleston (photo). Rootless corn (or rootless corn syndrome) occurs when there is limited or no nodal root development. Plants exhibiting rootless corn symptoms are often leaning or lodged. Affected corn plants may only be anchored in the soil by seminal roots or by a single nodal root. This condition is generally observed in plants from about the three leaf stage to the eight leaf stage of development. The problem often becomes evident when corn is subjected to strong winds, which result in plants falling over because there is a limited number or no nodal roots supporting them. The plants exhibiting floppy corn symptoms at S. Charleston last week had been subject to a thunderstorm the day before. The force of winds can also break off nodal roots and inhibit establishment of a permanent root system. Leaning and lodged plants (sometimes referred to as "floppy corn”) may also be wilted. When affected plants are examined, the nodal roots appear stubby, blunt, and unanchored to the soil.
Rootless corn problems are usually caused by weather related conditions that coincide with development of the permanent (or nodal) root system and various environmental factors. These include shallow plantings, hot, dry surface soils, compacted soils, and loose or cloddy soil conditions. Excessive rainfall and shallow plantings may cause erosion and soil removal around the crown region that can result in rootless corn.
“High crown syndrome” has been associated with rootless corn problems (http://bulletin.ipm.illinois.edu/article.php?id=1650). One of the causes of high-crown syndrome is subsidence of the soil due to rainfall after planting, when planting occurs in dry soils fluffed by tillage. If the planting furrow opens as soils dry after planting (this is most common in no-till), coleoptile growth stops and the crown can be set near the seed, essentially placing the seed and seedling above the soil (Nafziger, 2012).
The nodal roots develop above the seed and comprise the permanent root system of corn. The nodal roots, not the seminal roots (associated with the seed), are important in providing the water and the mineral nutrients that the corn plant needs for normal growth and development. If corn seed is planted 11/2 to 2 inches deep, then the nodal (or crown) roots begin develop at about 3/4 inches below the soil surface. However, if seed are planted shallower (1 inch or less), then the nodal roots may form near or at the surface where they are more exposed to fluctuations in soil moisture and temperature. Nodal root growth is very sensitive to high temperatures (w/ root growth slowing or stopping at soil temperatures exceeding 86 degree F). When unshaded surface soil temperatures reach the mid 90's or higher on hot days, the nodal root growth of shallow planted corn may stop. Plants are forced to rely on the seed root system or limited nodal root growth until more favorable temperatures and moisture conditions allow nodal root growth to resume.
Certain types of herbicide injury (e.g. 2,4-D, Banvel) and insect feeding (e.g. corn rootworm) may also cause lodging to occur in corn plants during vegetative development. Generally they are not the major causes of the rootless corn problems. However, there may be situations where insect feeding and/or herbicides may be a contributing factor.
Can rootless corn recover? Yes, after plants lodge, adequate rainfall will promote crown root development and plants can recover. Cultivation to throw soil around exposed roots may aid the corn's recovery. Of course, this is difficult to do in a no-till situation or when the soil is hard and dry. Since affected corn is likely to be vulnerable to potential lodging problems at maturity, it should be harvested as soon as grain moisture conditions permit.