Note: It is clearly too late in the season to correct nutrient deficiencies, thinking about these things now can help us to be more aware, thoughtful, and proactive next year.
A farmer called several weeks ago and said that his corn was looking ‘striped.’ The agronomic jargon for that condition is ‘interveinal chlorosis.’ Indeed, it was faintly, yet distinctly exhibiting those symptoms.
His theory was that it was sulfur or magnesium deficiency, which was a very reasonable starting point. Most farmers are somewhat familiar with various nutrient deficiency symptoms in corn:
Purple corn on cool soils usually indicates phosphorus deficiency (which is often temporary).
Yellowing and tissue death on leaf margins, beginning with lower leaves? Potassium deficiency.
Generally yellow and spindly plants; yellowing of leaves starting at the bottom and moving upward with time; yellowing begins along midrib and moves outward toward the margins; lower leaves and previously yellow tissue often in various stages of death: Nitrogen deficiency.
In this field, however, the lower leaves were deep green, and the upper leaves tended to be more striped. Looking at an individual plant, the symptoms were similar to sulfur deficiency, but basically every plant in the field had the same symptoms — there were no patches where the corn looked ‘normal.’ Ordinarily, I would expect a sulfur deficiency to be on sandy soil and to be patchy/localized. Manure applications are never perfect, so corn in areas where manure was applied heavily is much less likely to show symptoms. However, nobody had seen/noticed a sulfur deficiency on this field before, it receives manure (a good source of sulfur) and the soils were warm (which often increases sulfur availability and results in sulfur deficiency symptoms disappearing). Together these things were pointing to hybrid (genetics) interacting with environmental effects without a clear connection to a particular nutrient deficiency.
When in doubt, taking a tissue test can reveal the nutrient deficiency that is responsible for the deficiency. Ideally, a separate composite sample will also be collected from asymptomatic plants in the same field and of the same variety, but in this case there were no asymptomatic plants. Given the stage of maturity, rather than collecting whole plants or ear leaves, we collected 20 youngest fully developed leaves from around the field. The leaves were submitted to Cumberland Valley Analytical Laboratory via the feed company. The analysis showed that while boron, manganese, and magnesium were on the lower range of the sufficiency range, the symptoms were not consistent with deficiencies of any of those nutrients. Sulfur (the primary suspect) concentration was toward the middle of the sufficiency range, and the N:S was about 14:1, which is not problematic. One caveat I will add is that there is an interesting theory floating around that with the yield potential of modern corn hybrids, the ‘sufficiency range’ should be indexed to yield potential, i.e., the sufficiency range for corn grown in a context where it is headed for 17 tons/acre will be different from corn at the same developmental stage that is headed for 30 tons/acre. That said, published sufficiency ranges might not be nuanced enough and may need refining.
The aforementioned farmer had the same hybrid planted in another field located 30 minutes from the home farm, and the plants in that field exhibited the same symptoms. At this point everything is pointing toward variety X environmental effects. Since then, I have seen a couple of other farms with similar symptoms in their fields.
Internet searches will reveal various articles discussing plants with symptoms discussed above. Richard Taylor (University of Delaware) has observed the phenomenon in Delaware and Greg Binford (Wilbur-Ellis, formerly at University of Delaware) has observed similar things in the Midwest. While they lean toward a sulfur-involved hypothesis, they believe that there is a varietal aspect, yet acknowledging that grain yields from fields with ‘symptoms’ can still exceed 300 bushels/acre (which is phenomenal). At the same time, intuitively, yellow stripes suggest less chlorophyll, which makes one wonder about less photosynthesis and compromised yield.
What to do? Take a look at your fields and let me know if you see these symptoms in any of your fields. If you do, please let me know which varieties are exhibiting the symptoms. Maybe we can find a pattern and better understand what is going on, whether it is a concern, and how to deal with it. Contact: firstname.lastname@example.org or by phone at 802-535-7922. To view additional photos please visit https://agronomator.wordpress.com