round the state, some corn growers are lamenting the fact that fields of corn that had emerged uniformly and initially developed uniformly are now fields that contain plants of uneven color and size. What can cause this transformation?
Almost invariably the cause lies below ground. Early last month, I briefly reviewed the initial root development process in corn. In that article, I emphasized the importance of maintaining the health of the seed and the mesocotyl until the nodal root system was successfully established.
As the nodal roots develop, the importance of the seed reserves and the mesocotyl (the 'pipeline' to those reserves) declines. If a field of corn successfully develops to about the V4 (four visible leaf collars) stage with no damage to the mesocotyls or seed, chances are that the field will look very uniform. For all practical purposes, the time from planting to about V4 to V6 can be labeled the 'stand establishment' period for corn.
Without access to the seed reserves during stand establishment, a seedling will either die or become severely stunted. Consequently, a field that may have emerged uniformly and initially looked quite uniform may become very uneven in appearance if initial seedling development has been affected by one or more stresses.
The list of potential stresses that can injure the seed, seed roots or mesocotyl is not particularly long, but deciding which ones to blame can be difficult since more than one is usually present in any given field. The list of possible offenders includes:
Other factors that influence the effects of these early stresses include cool soils in general, sandblasting injury, excessively dry conditions and ponding. All of these weather-related stresses slow or hinder the early growth of corn seedlings and make them more vulnerable to the above list of stresses. Similarly, while most herbicides that can injure corn do not do so to such young seedlings, later injury will subsequently hamper the recovery of an already struggling crop.
Seed quality and the hybrid's inherent seedling vigor also play an important role in determining the consequence of injury during stand establishment. Otherwise minor stresses during stand establishment can have major effects on overall plant health if seed quality is less than acceptable or if seedling vigor is simply average.
The bad news is that if stand establishment this year is crappy (an agronomic term meaning uneven), there is little you can do about it now. As you think about next year, there are a few things you can keep in mind to minimize the future risk of crappy stands.
Corn planting began very early in Indiana this year due to warm temperatures and little to no rainfall in late March and early April. Earlier than normal planting always comes with a greater risk of lengthy germination and emergence periods. Indeed, many fields planted in early April did not emerge for three to four weeks as temperatures reverted to their fairly normally cool levels for much April and early May. Even fields planted in late April were slow in developing throughout much of May.
Any time that germination, emergence AND stand establishment are delayed significantly, the developing crop is similarly exposed to a lengthier period of stresses from the list above. The consequence of such stresses on a slowly developing crop is exactly the uneven stands of corn that some corn growers are lamenting about now.