Yellow Corn Plants Showing Up In Many Fields

Yellow Corn Plants Showing Up In Many Fields

Above-normal rainfall across Iowa has growers wondering if their corn fields have enough nitrogen left. There are several possible reasons for corn plants showing various shades of yellowing and interveinal leaf stripping.

So far, the early part of the 2011 growing season has had considerable cool and wet conditions. Many fields as of June 13 have corn plants showing various shades of yellowing and interveinal leaf stripping. What may be the cause? John Sawyer, Iowa State University Extension soil fertility specialist, lists the following answers and observations.

1. Cold temperatures. Not uncommon with early corn planting. Entire small plants can show lack of green color.

2. Wet soils. Corn roots need aerated soil for metabolic processes and nutrient uptake. Entire plants can show yellowing and many different symptoms, including phosphorus deficiency.

3. Slow soil organic matter mineralization. With cold temperatures, microbial conversion of organic nitrogen (N) compounds to inorganic N (ammonium and nitrate) is slow. If the corn plants are dependent on that source of plant available N, then plants could show N stress. Entire plants can show yellowing.

4. Sulfur (S) deficiency. This is related to item 3, that is, slow organic matter mineralization and lower supply of plant available sulfate-S (the form of S taken up by plants). Soil organic matter is the largest reserve of S in most soils, so slow mineralization can limit available sulfur, especially in the upper soil profile.

There have been several examples of early season response to sulfur application (greener plants) in on-farm strip trials and research plots at experiment stations this spring (Kanawha, Muscatine and in central Iowa). In some cases, these early sulfur deficiency symptoms may disappear with time and there would be no yield consequence. "Our ISU research the past few years indicates this doesn't always occur, and about 60% of the research trials have had a yield increase with S application, especially when the deficiency symptoms are severe," he says.

For more information on Iowa sulfur research in corn, see the ISU Integrated Crop Management conference report, Dealing with Sulfur Deficiency in Iowa Corn Production. Classic sulfur deficiency in corn is when the older leaves are green and the new leaves show yellowing and interveinal stripping. With severe deficiency, the entire plant will be yellow.

5. Continuous corn. In many springs, and again this year, corn following corn tends to show more yellowing than corn following soybean, especially in reduced till and no-till. This is related to many factors, such as same crop allelopathy and less mineralization (for N and S).

6. Potassium deficiency. It typically begins to show on larger plants, about calf to knee high. Symptoms appear first on older leaves, with yellow to brown coloration on the leaf margins.

7. Corn hybrid. Some corn hybrids tend to show interveinal stripping more than other hybrids, and hybrids have different levels of greenness.

Nutrient deficiency symptom pictures and descriptions can be found in ISU Extension publication, Nutrient Deficiencies and Application Injuries in Field Crops, IPM 42.

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