by Leah Ten Napel

When we walk into a field of corn, we hope to see dark green plants growing strong. This tells us that those plants most likely have a sufficient amount of the nutrients they need and adequate growing conditions.

Unhealthy corn plants may start to show nutrient deficiency symptoms that include:

In this article, we’ll dive into how to spot these nutrient deficiencies. But first, let’s talk about other factors that can cause similar symptoms on a corn plant. We may start to see unhealthy corn plants because of issues within the root system. Injured roots can result from compaction, feeding from insects, diseases, or burns from chemicals or fertilizers.

One soil attribute that can affect the availability of nutrients is the soil pH. A high or low pH value can reduce the uptake of nutrients that cause deficiency symptoms, even though nutrients are present in the soil. The optimum soil pH for corn production is between 6 and 6.5.

Other soil attributes that can mimic deficiency symptoms are texture, cation exchange capacity and organic matter. If a nutrient is present in the residue but slow to release, we also may see deficiency symptoms on the plant.

One important factor to consider during the growing season is moisture. In dry conditions, a plant may appear nutrient deficient, especially if moisture is required to uptake that nutrient into the plant. We can determine true nutrient deficiencies by taking tissue samples during the growing season or soil samples prior to planting.

After determining a nutrient deficiency exists, we can evaluate the symptoms. Mobility of the nutrient affects where the symptoms appear on the plant. Mobile nutrients present in the older leaves and move to the new leaves to maintain new growth. Therefore, deficiency symptoms appear in the older leaves first. These nutrients are nitrogen, phosphorus, potassium and magnesium.

Nonmobile nutrients will show symptoms on the younger leaves first because they do not move as easily throughout the plant. These nutrients are zinc, sulfur, calcium, boron, iron, manganese, copper, molybdenum and chloride. If a symptom is appearing on all leaves, it may be a sign of herbicide injury, drought stress or disease.

Missing nutrients

Corn can be lacking in these nutrients:

Nitrogen. Nitrogen deficiency causes pale, yellowish-green corn plants with spindly stalks. Because nitrogen is a mobile nutrient in the plant, symptoms begin on the older, lower leaves and progress up the plant if the deficiency persists. Symptoms appear on leaves as a V-shaped yellowing, starting at the tip and progressing down the midrib toward the leaf base.

Phosphorus. Phosphorus deficiency is usually visible on young corn plants. It readily mobilizes and translocates in the plant. Plants are dark green with reddish-purplish leaf tips and margins on older leaves. Newly emerging leaves will not show the coloration.

Phosphorus-deficient plants are smaller and grow more slowly than plants with adequate phosphorus. Deficiency symptoms almost always disappear when plants grow to 3 feet or taller.

Potassium. Potassium deficiency is first seen as a yellowing and necrosis of the corn leaf margins, beginning on the lower leaves. Symptoms usually don’t appear for some time after planting (about four to six weeks, around the V6 growth stage).

If the deficiency persists, symptoms progress up the plant because potassium is mobile in the plant and translocates from old to young leaves. When potassium deficiency is severe, older leaves turn yellow with tissue necrosis along the margins, but the upper new leaves may remain green.

Magnesium. Magnesium deficiency is first seen as yellow to white interveinal striping of the lower corn leaves. Dead, round spots sometimes follow, which give the impression of beaded streaking. Older leaves become reddish-purple, and the tips and edges may become necrotic if the deficiency is severe. This happens because magnesium is mobile in the plant and is translocated from old to new plant tissue.

Zinc. Zinc deficiency in corn causes interveinal, light striping or a whitish band beginning at the base of the leaf and extending toward the tip. The margins of the leaf, the midrib area and the tip usually remain green.

Plants are stunted because internodes are shortened. Zinc is relatively immobile in the plant. Severe zinc deficiency may result in new leaves that are almost white, an effect termed “white bud.” Plants frequently outgrow zinc deficiency unless it is severe.

Sulfur. Sulfur deficiency shows on small corn plants as a general yellowing of the foliage, similar to nitrogen deficiency. Yellowing of the younger upper leaves is more pronounced with sulfur deficiency than with nitrogen deficiency because sulfur is not easily translocated in the plant. Stunting of plants and delayed maturity also are symptoms. Interveinal chlorosis of the youngest leaves may occur.

For more information

Descriptions used for this article come directly from a field reference written by John Sawyer, a retired Iowa State University Extension soil fertility specialist.

You can find “Nutrient deficiencies and application injuries in field crops,” IPM 42, at store.extension.iastate.edu; search for IPM 42 in search box.

Ten Napel is an ISU Extension field agronomist.