Wet conditions recently could lead to some issues in corn that may start showing up over the next few weeks. For example, producers may be seeing corn that is falling over or flopping in the wind this year. Occasionally plants are standing, but exhibit wilting or stunting symptoms. To diagnose the problem, start by digging up some plants and examining the root system. Corn in the V4 to V6 stages and beyond should have a well-established secondary root system. These are larger and thicker than the primary roots. If the corn plants have not established a viable secondary, or nodal, root system, the problem is often termed “rootless” or “floppy” corn.
Figure 2. Plants with adequate (left) and poor root development (right) systems. Photo by Ignacio Ciampitti, K-State Research and Extension.
When corn germinates, the first roots to emerge from the seed are the primary, seminal, or seed roots. These roots support the plant through emergence and the appearance of the first few leaves. At emergence, exposure of the coleoptile to light will cause it and the mesocotyl to stop growth and will position the crown at ¾” to 1” or more below the soil surface. As the plant grows, the first four or five nodes do not elongate, keeping the growing point below the soil surface until V6 when the stem begins to elongate rapidly.
The roots that develop from these compressed nodes at the crown form the secondary root system. This is a bit confusing because this “secondary” root system is of primary importance for the rest of the life of the corn plant. It is called secondary because it is the second to appear chronologically. These secondary roots rapidly take over water and nutrient uptake and are important for anchoring the plant as it moves through the V4 to V6 growth stages and beyond. If something prevents establishment of these secondary roots, the plants can fall over or flop in the wind or the plants may be stunted or wilted.
Several situations may cause poor secondary root development:
- Saturated soils may prevent adequate root development.
- If the surface soil dries rapidly just as the secondary roots begin to grow, the roots desiccate and the tips die before they reach more moist soil below.
- If the crown becomes exposed for any reason, the secondary roots can dry out and die before they grow into the soil. Crowns can be exposed if heavy rains have compacted the seedbed or washed away the soil (erosion) from around the developing crown.
- Occasionally the mesocotyl (the connection between the seed and the crown) will continue to grow after the coleoptile emerges from the soil, causing the crown to be positioned close to or at the soil surface. The reasons for continued growth of the mesocotyl and the resulting exposed position of the crown are poorly understood. Some believe it could be due to growth-regulating herbicides (e.g., 2,4-D, dicamba) or cloudy conditions, but cause-effect relationships have not been well established. Several instances of exposed crowns have been documented with no application of growth-regulating herbicides.
- Shallow planting could be the cause of the problem in a few cases. Although shallow planting can cause exposed crowns and poor secondary root development, most fields observed this spring with “rootless” corn have been planted at an adequate depth.
Is there any hope for “rootless” or “floppy” corn? Possibly, depending on whether soils are able to dry out enough to provide good aeration for the roots. Even if plants have fallen over, new secondary roots can continue to form and establish a viable root system if soil aeration and moisture conditions are adequate. Inter-row lay-by cultivation to move soil around the exposed crowns can help if not too many plants have fallen over.