One of the more unusual problems associated with hot, dry weather is "rootless" corn (also referred to as rootless corn syndrome by some investigators). The problem concerns plants with poorly developed root systems and is usually observed in plants from about the three leaf stage to the eight leaf stage of development. The problem has been described in corn fields from Iowa to South Carolina. Plants exhibiting rootless corn symptoms have either lodged or are ready to lodge. Sometimes the corn will only be anchored in the soil by a single nodal root or by seminal roots. Before the problem is evident, corn plants may appear vigorous and healthy, but after a sudden storm with strong winds, plants will be scattered or fall over because there is limited or no support. Leaning and lodged plants may also be wilted. When affected plants are examined, they are found to lack all or most nodal roots. The nodal roots present appear stubby, blunt, and unanchored to the soil.
Under favorable growing conditions, the nodal roots (crown or secondary 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.
Many investigators have attributed rootless corn problems to weather related conditions, that coincide with development of the permanent root system, and other environmental factors. These include hot, dry surface soils, shallow plantings, compact soils, loose, or cloddy soil conditions. Nodal root development is inhibited by hot, dry compact soils. The abrasive action of strong winds has also been observed to break off secondary roots and inhibit establishment of a permanent root system. Excessive rainfall and shallow plantings may cause erosion and soil removal around the crown region that can result in rootless corn.
Although certain types of herbicide injury and insect feeding may cause lodging to occur in corn plants during vegetative development, there has generally been little evidence of their involvement in these rootless corn problems. Nevertheless, there may be situations where insect feeding (e.g. corn rootworm) and/or herbicides (e.g. 2,4-D, banvel) contribute to rootless corn problems.
Can rootless corn recover? Yes, after plants lodge, adequate rainfall will promote crown root development and many plants can recover. Iowa investigators report that cultivation to throw soil around exposed roots will 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.
Prepared by:
Peter R. Thomison
Extension Agronomist
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