Yellow corn in Virginia has been suffering

Published 9:56 am Wednesday, June 15, 2016

Many of the corn fields on the Eastern Shore and in Eastern Virginia are “yellow” and stunted due to the weather this spring (Figs. 1 and 2) and is similar to conditions that Virginia farmers experienced in Spring 2010. There are many reasons for the corn to be yellow that range from nutrient deficiencies to abiotic factors. Some reasons for yellowing include:

1. Cold temperatures. This spring’s temperatures are below normal. Yellow and purpling of corn is a common occurrence with cool weather. Yellow corn may seem to be a nutrient deficiency issue; however, the corn in Figs. 1 and 2 were tested and have adequate nutrient concentrations. Actually, due to the concentrating effect of stunted growth, several nutrients like phosphorus (P) and nitrogen (N) have very high concentrations.

2. Wet soils. Virginia farmers went from a drought situation in March-April to non-stop rain in May. Saturated soils reduce aeration corn roots need for metabolic processes and nutrient uptake. During wet conditions, the entire corn plant may show yellowing and other different nutrient deficiency symptoms, such as purple leaves from P deficiency.

3. Lack of sunshine. This definitely interacts with the first two factors. Corn plants convert sunlight to energy, which in turn drives growth and metabolism. The long stretches of cloudy days in 2016 have definitely contributed to the overall poor growth and lack of vigor.

4. Nitrogen deficiency. Many farmers utilize organic fertilizers, such as poultry litter or cover crops, as starter N fertilizer for corn production. Microbial conversion of organic N compounds to inorganic N (ammonium and nitrate) is slow during cold and wet soil conditions. Corn plants dependent on organic N will show N deficiency in cool wet years compared to normal weather years. Also, sandy soils may experience leaching as N moves down the soil profile with rain water. Heavier textured soils and areas that pond water can quickly become saturated. These saturated fields may lose N via denitrification.

Nitrogen deficient plants will show a general overall yellowing and stunted growth.

5. Sulfur (S) deficiency. Overall, S reacts very similar to N in the soil system. Slow organic matter mineralization will reduce available sulfate-S concentrations (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 S, especially in the upper soil profile. Sulfate can also leach down the soil profile with rain water during large rain events. In figure 6, poor growth led to a N concentration effect; which increased the N:S ratio that could also cause corn yellowing since the ratio is higher than 15 parts N to 1 part S (>15:1).

6. Potassium (K) deficiency. Potassium deficiency symptoms typically show up on larger plants, about knee high. The K deficiency symptoms appear first on older leaves, with yellow to brown coloration on the leaf margins.

7. Soil pH. The optimal pH for corn is between 6.0 to 6.5. However, we have seen reports with soil pH as low as 4.5. In a low pH field, acidic soil conditions solubilize aluminum that can damage the corn’s roots; which inhibits nutrient and water uptake. The lack of nutrients can stunt corn and cause deficiency symptoms to appear. Soil pH problems will often first appear in lighter, sandier textured areas while the heavier soils look to be growing normally (Figure 3).

8. Corn hybrid. Some hybrids tend to show interveinal stripping more than other hybrids, and hybrids have different levels of greenness. Figure 4 shows a field planted on the same day with varying of corn greeness.

Care should also be taken when using visual deficiency symptoms to diagnose crops. Visual characteristics are a start, but may be misleading as many nutrients exhibit similar symptoms that can easily be confused. For instance, many fields appear stunted and yellow and are diagnosed as a nitrogen deficiency when in fact sulfur deficiency is the main culprit. Likewise, stunted plants from cool and wet conditions may appear to look like the classic magnesium deficiency stripe that you find in nutrient management guides and on internet searches. The best way to diagnose nutrient deficiencies is to use tissue and soil testing. Many private labs can email or fax results back within a day or two after sample submission. For around $25, tissue tests will give exact nutrient concentrations and pinpoint what nutrients may be in short supply. Soil tests will show what the plant is actually able to secure from the soil in this growing season.

For more accurate recommendations, submit a soil sample along with your tissue tests. For corn less than 12 inches tall, take 30 samples from the whole aboveground portion across the entire field. Between 12 inches tall and tassel, sample the upper-most fully developed leaf (leaf has a “collar”). Take a soil and tissue sample from both the “good” and “bad” area of the field. This will allow you to compare differences in your specific situation versus depending on book values from across the USA. Overall, the time and money it takes to test your corn is small compared to the fertilizer inputs you have already or will potentially invest. Also, sampling will ensure that you do in fact have a nutrient problem versus yellow and stunted corn from cool and wet weather.

To correct nutrient deficiencies, macronutrients (N, P, K, magnesium, and S) and micronutrients (zinc, boron, and manganese) important for corn production can be mixed into your side dress application when plants are knee-high. For farmers not applying side dress applications or are past this stage, foliar feed applications can be made and possibly incorporated with other maintenance sprays. Be sure you consult your tissue test recommendations, Virginia Cooperative Extension, or your local fertilizer dealer for recommended rates and products. Remember: Too much is not always better and source is important. Some nutrient sources have the potential for leaf burn which is not desirable for a plant already under nutrient stress. The correct source and rate are critical to efficiently correcting the nutrient deficiency.

As always, the best way to correct a deficiency is to avoid it in the first place. All fields should be routinely soil sampled and fertilizer applied based on your soil’s yield potential. Using Virginia Tech’s soil testing laboratory, your soil’s yield potential will automatically be calculated if you put your soil series on the soil sampling sheet instead of yield goal. Proper nutrient management can save more than headaches, it can reduce unnecessary fertilizer use, increase yields, and increase profits.

For more information on proper fertilizer use and placement in field corn, consult Virginia Cooperative Extension publications No. 424-027 (nitrogen and phosphorus), No. 452-702 (macronutrients) and No. 452-701 (micronutrients).

This article was compiled by the following:

Mark S. Reiter 1, 2; W. Hunter Frame 2, 3; Wade E. Thomason 2; J. Scott Reiter 4; and Janet Spencer 5

1. Eastern Shore Agricultural Research and Extension Center, Virginia Tech

2. Department of Crop and Soil Environmental Sciences, Virginia Tech

3. Tidewater Agricultural Research and Extension Center, Virginia Tech

4. Prince George County, Virginia Cooperative Extension

5. Isle of Wight County, Virginia Cooperative Extension