Why "Rootless" Corn is so Prevalent in Drier Areas this Year - UNL CropWatch, June 2012

Why "Rootless" Corn is so Prevalent in Drier Areas this Year - UNL CropWatch, June 2012

Patch of corn exhibiting "rootless" syndrome

Figure 1.  Patch of corn in south central Nebraska exhibiting "rootless" syndrome.  (Photos by Brandy VanDeWalle)

 June 8, 2012

There are many reports of “rootless corn syndrome” extending from western and central Nebraska to Indiana (Figures 1-2). While there are many contributing causes, most of them relate to soil moisture at and during the first four weeks after planting. Let’s think about the development of corn roots, then consider the “rootless” issues.

Rootless corn

Figure 2. Dry soils likely led to poor root development in corn in some fields in western and south central Nebraska. Without good root support, plants lean or fall as they grower taller or face high winds.

When a corn seed germinates, the first structure to emerge is the radical, followed by two to five seminal roots. The radical is oriented more or less randomly (except up), depending on the direction of the kernel tip. The early developing seminal roots orient themselves downward (in response to gravity). A day or so later the coleoptyl and mesocotyl, the shoot, emerges and orients itself upward. Depending upon hybrid and soil conditions, the seminal roots branch and take up moisture and nutrients for the developing seedling. Shortly after emergence, the nodal (or crown) root system begins to develop. It is these nodal roots that become the permanent root system. More roots develop from successive nodes as the plant develops.

However, if the soil next to the root node is dry, hard, cloddy, or otherwise inhospitable when the first ring of roots is attempting to develop, there will be little effective growth. Often the tissues trying to develop into roots look like little “warts” of hard tissue at the node. Typically, if sufficient moisture is available below, the seminal roots and radical allow the first three or four leaves to develop. However, as the plants grow taller or with the first wind, the plants will have insufficient anchorage to stand.

Causes of Rootless Corn Syndrome

Lots of conditions have been observed to cause this rootless appearance, most of them related to weather or planting. Planting too shallow (less than 1.5 inches) can be a problem, especially if heavy rain compacts or erodes the soil. When disc openers were first used on planters, rootless corn syndrome was labeled “max-emerge disease.” This was because disc openers enabled farmers to plant in wetter soil conditions, which resulted in furrow sidewall smearing or compaction. This sidewall area can become hard and dry, causing nodal roots, if they develop, to grow parallel to the planted rows. More often, there is little nodal root development and plants lodge at the 3- to 5-leaf stage. Dry weather and wind are usually involved, especially on the Great Plains.

Adjust Planter to Avoid Problem Next Year

In reviewing the increase in "rootless" corn reports this week, UNL Extension Cropping Systems Specialist Greg Kruger agreed with Dr. Hoegemeyer that the problem often relates back to planting depth and noted:

The reason that rootless corn is often “patchy” across a field (Figure 1) is because the planter is properly calibrated for parts of the field, but in areas of heavy soils, compaction, or in other areas that may push the planter units up, the seeding depth is too shallow for root development.

Ultimately, the true test of rootless corn would be to dig the plants and look at the root systems. Root systems will often appear underdeveloped for the size of the plant and the brace roots will generally not be developing like they should be.

If you find yourself victim to rootless corn, next year add a little more down pressure or set the planter one notch deeper.
 

When soils in the top inch become hot, very dry, loose, and granular, especially after dry winters or springs and following soybeans, rootless corn can develop, This can occur regardless of crop rotation or tillage, but especially if soils dry rapidly to tilled depths

Management

If pivot irrigation is available, planting at 2-inch depths, followed by timely, moderate irrigation can often prevent the problem. An issue that was pointed out by Emerson Nafziger of the University of Illinois is that the root crown and nodal roots can be “set high” due to rapid growth in warm soils. When the tip of the shoot (coleoptyl) emerges from the soil and light strikes it, the nodal roots form where the growing point is at at that time, usually about ¾ inch to 1 inch below the surface. If soil conditions are not suitable, the roots at the first node fail to develop properly. If corn grows very rapidly in warm soils, the tips of the coleoptiles do not stop growing at night, and by the time light reaches them, the growing point (and this root node) are already near the soil surface. Because of the unusually warm spring in 2012, this may have contributed to the situation this year.

Pivot irrigation and/or cultivation are probably the only management tools available. However, cultivators are no longer available on many farms, and irrigation is not universally available. If rain or irrigation provides moisture to the soil surface, after the plants lodge, many plants will form nodal roots and “stand themselves up.” However, these plants may not form fully normal root systems and may be vulnerable to heat/moisture stress and nutrient deficiencies, even under good growing conditions. There is also increased risk of lodging in the fall.

Tom Hoegemeyer
Professor of Practice, Department of Agronomy