fter
a delayed start due to excessively wet field conditions, corn planting progress
in Indiana accelerated during the past three weeks as the rains subsided (Fig.
1). That’s the good news. The bad news is that the rains have subsided (Fig
2). That fact plus mid-summer temperatures, low humidity levels, and frequently
windy days have combined to quickly dry out surface soil in many fields (Fig.
3) and the young corn crop is feeling the effects.
The
excessive drying of the upper soil profile is conducive for the development
of what some of us affectionately call the “rootless corn” or “floppy corn”
syndrome. The problem illustrates a classic example of the importance of the
timing of stress and plant development.
The permanent (nodal) roots of a corn plant develop initially from near the crown area of the plant (Nielsen, 2007a). They develop sequentially in sets or “whorls” from individual nodes of the stalk. The growing point or meristem of a root lies near the root tip and must remain alive in order for the root to develop normally.
Contrary to popular opinion down at the coffee shop, roots do not grow toward moisture on purpose. They grow downward in response to gravity (i.e., a gravitropic response). If nodal roots begin development in bone-dry surface soil but elongate into soil moisture at deeper depths prior to desiccation of the root tip, then the root will survive and proliferate.
If the root tip (and accompanying meristem) desiccates prior to reaching soil moisture, the entire young nodal root will likely die. This is particularly true if the axillary meristems along the length of the root (that eventually produce the branch roots) have not yet differentiated or become active.
The
appearance of such a desiccated root is what one would imagine; shriveled and
discolored. This symptom is unlike that of any other lethal root stress, including
salt injury from fertilizer. These symptoms are NOT like any associated with herbicide injury or
insect feeding. Because several sets of roots may not have formed belowground,
the crown may "appear" to be at or above the surface. That appearance
is an optical illusion except in a few cases (Nielsen,
2004).
Entire
sets or “whorls” of nodal roots sometimes die in this manner and the plant essentially
survives on what’s left in the kernel reserves and what the seminal roots offer
in terms of moisture and nutrient uptake until the next set of nodal roots develop
and become established. If subsequent sets of nodal roots die in the same manner,
the plant continues its dependence on the kernel and seminal root support.
In fact, it is amazing to me how the aboveground appearance of a plant affected with the “rootless” syndrome can remain fairly normal up until the windy day when the mesocotyl simply can no longer support the plant and it flops over to the ground. “Floppy” corn plants are NOT technically root-lodged; they are simply broken over at the mesocotyl below the crown area of the plant. Obviously, the health of the mesocotyl and the seminal roots determine whether an affected plant can “hang on” until a decent soaker occurs to replenish soil moisture levels.
 Example of "floppy corn" syndrome. |
 Closer view of "flopped" plant. |
 Desiccated, dead nodal roots. |
 Closer view of desiccated, dead nodal roots and broken
mesocotyl. |
What Can Be Done? Unfortunately, very little can be done to prevent the situation from becoming worse. Row cultivation may encourage new nodal root development if moist soil is thrown around the base of the plants. However, if the soil is dry enough to be causing the problem in the first place, there's probably very little moist soil shallow enough to be brought up by row cultivation. The ultimate solution to the problem is a good soaking rain or at least enough of a rain to sustain new nodal root development long enough to allow the roots to reach deeper and hopefully wetter soil conditions before the upper soil dries again.
 Mid-April planted corn at V4-V5 leaf stage on 20
May. |
 Nodal roots of "normal" plant. |
 Dry, cracked soil around base of V4 plant. |
 Limited nodal root system associated with "rootless
corn" syndrome. |
 Closer view of desiccated, dead nodal roots. |
A “Hindsight” Reminder. “Rootless” corn can also be aggravated by extremely shallow seeding depths that result in nodal root initiation beginning near the soil surface rather than at the usual ¾ inch depth. This is one of several reasons that growers should avoid choosing seeding depths shallower than about 1 to 1½ inches.
Elmore, Roger and Lori Abendroth. 2007. Rootless Corn Syndrome. Integrated Crop Management Newsletter, Iowa State Univ. [On-Line]. Available at http://www.ipm.iastate.edu/ipm/icm/2007/5-21/rootless.html. (URL verified 5/23/07).
Nielsen, R.L. (Bob). 2004. Over-Extended Mesocotyls and Floppy Corn Syndrome. Corny News Articles, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/articles.04/FloppyCorn-0624.html. (URL verified 5/23/07).
Nielsen, R.L. (Bob). 2007a. Root Development in Young Corn. Corny News Articles, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/timeless/Roots.html. (URL verified 5/23/07).
Nielsen, R.L. (Bob). 2007b. Variable Emergence Due to Variable Seedbed Moisture. Corny News Articles, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/articles.07/VariableEmergence-0520.html. (URL verified 5/23/07).
