Why the Yellow Corn ??

In the last few days much of the early planted corn has turned “ugly” – yellow, some leaf striping, perhaps some unevenness. Many of these fields looked good to excellent prior to this current stretch. What is going on?

I think there are two primary categories:

1) Heavy, poorly drained soils: “WET FEET”. Many of the corn plants that were planted in mid April looked good, until they went through about 4 weeks of wet and cool weather. In poorly drained soils, or in soils that were compacted from working too wet or from heavy wheel traffic, roots are restricted and not growing well into starter fertilizer bands or not yet into nitrogen fertilizer. These fields should green up and even out somewhat as growing conditions improve and roots systems expand.

2) Light soils – sands and sandy loams, low organic matter: INADEQUATE NUTRIENT UPTAKE DURING A MAJOR TRANSITIONAL GROWTH PHASE . Most of the corn I’ve seen in this category is from V2-V4. The corn plant is transitioning from feeding primarily off the seed and via the seminal root system (the roots which grow out of the seed piece). During this period, it is essential to have a good enough root system and sufficient available nutrients in the root zone in order to avoid nutrient deficiencies.

Given a period of slow growth due to the cool weather of most of May followed by the very warm weather of last week, the plant ended up under stress. Nodal, or permanent root systems, were not yet sufficient to provide adequate nutrients. This situation is compounded in low organic matter sands.

Specific issues may include nutrient deficiencies, possibly nitrogen, sulfur, zinc, magnesium, and perhaps others. Slow growth, leaf striping, and yellowing are all symptoms. Limited plant tissue analysis suggests sulfur as a major deficiency. Sulfur deficiency is very possible even if sulfur fertilizer was added to the starter fertilizer.

Nutrient deficiencies may be compounded by low pH. Sandy soils often have pockets of low pH, even if the whole field pH reading is adequate.

While I do not think it the primary cause of the widespread yellowing, corn nematodes might be to blame in some areas. Nematodes are difficult to assess. They generally cause stunting and yellowing of small corn. If the symptoms you see are in small, oval shaped areas in fields, it is worth sampling for nematodes.

Is there anything to do about the yellow corn? Probably not at this time. Given good growing conditions, most fields should green up nicely as root systems expand and get into starter fertilizer bands and/or nitrogen fertilizer. Soil and tissue sampling and analysis may be useful to more specifically identify the issue(s) and to develop a plan for next year. Foliar fertilizer applications may be helpful, but it is usually impossible to get enough nutrients into the plant in this manner to make a significant difference. Application of granular amendments such as gypsum or some of the sulfur-potash-magnesium products may have some benefit, but are no guarantee. I recommend caution in spending too much money to try to fix an issue which will likely fix itself over the next week or two.

Call us if you want us to look at your fields or to discuss your particular situation.

If you have any questions or concerns please contact:

Terry Jones, Regional Agronomist @ 419.346.7786 or tmj@brodbeckseed.com or

Rod King, Regional Agronomist @ 574.596.6721 or rking@brodbeckseed.com