During June, farmers in Iowa saw cornfields with areas that were stunted and the lower leaves yellowing and turning brown along the margins. "This is a symptom of potassium deficiency, but it is often due to poor root function rather than a shortage of K in the soil," says Brian Lang, ISU area crop specialist at Decorah in northeast Iowa.
The end rows are often better than the rest of the field, probably due to the different soil structure where the traffic and/or tillage pattern has been different. Usually the fields look fine until the corn gets to about V5, then corn plants in areas of the field stop growing and the lower leaves turn yellow and/or leaf margins turn brown. "Good corn can be right next to extremely stunted corn with no apparent reason for it," says Lang.
Anything that restricts root growth during the initiation of the nodal root system can lead to this problem, says John Sawyer, ISU Extension agronomist at Ames. The nodal roots emerge within an inch of the soil surface. If there is something in the surface inch or so that the roots donâ€™t "like" they donâ€™t function properly.
Another possible reason for problem
Premature death of the mesocotyl and/or problematic development of the initial "seed roots" can also contribute to this problem.
"There can be large differences among hybrids in showing this phenomenon," says Sawyer. Shallow planting and/or soil settling or eroding after planting aggravates the problem.
If the soil hasnâ€™t been tested recently, soil samples should be taken to make sure it is not a true K deficiency problem. Soils that are low or marginal in K are more likely to show the problem.
In many fields it is difficult to come up with an explanation why the problem is appearing. It is most common in no-till fields, but shows up in tilled fields as well. In tilled fields, it can show up where the soil is fairly "fluffy", especially under dry conditions. Since the end rows usually look better, it could be that a little surface compaction actually helps to alleviate the problem.
ISU research agronomist Antonio Mallarino has an article in a recent ISU Integrated Crop Management newsletter explaining this problem further. Click on www.ipm.iastate.edu/ipm/icm/.
Poor brace root development of corn
Twisted corn and poor initial brace root development have been common in some cornfields this summer. "I have been in a few fields recently that showed what would be considered "early" brace root development, and the development is highly disoriented," says Brian Lang. "These brace roots are sometimes fused and/or sometimes the brace roots are growing upward."
This symptom is highly associated with the application of growth regulator herbicides, says ISU weed control specialist Mike Owen. There will be concern as to how the second set of brace roots develop to anchor the corn plant into the soil. This and related factors are discussed in an article by Owen at www.weeds.iastate.edu/weednews/2005/twisted%20corn.htm.