Corn green, yellow or purple?

Tony Nye - OSU Extension

I think my brain is becoming water-logged and creating crazy thoughts. I was wondering the other day if there was a way to plug the clouds for a while to prevent rain.

We tried seeding clouds for rain during droughts, so I just wonder if we can plug up a rain cloud. I know we can use something like bentonite to help seal leaking ponds. Do you suppose we could fly up into the clouds and dust them with bentonite?

My only other solutions would then be to move away to somewhere less rainy or build a giant dome over top of us and create our own environment.

Oh well, think sunny, dry weather. Maybe we can change the pattern through telepathy.

As corn is emerging and beginning to grow, we are beginning to see some variability developing within the same field. This includes a multitude of colors according to Peter Thomison, Ohio State university corn specialist.

If you drive around enough, in any given field, corn can appear dark green in sections, while other sections are yellow and occasionally purple. Does this mean producers should be overly concerned?

Thomison suggests the yellowing could be due to low nitrogen or sulfur uptake and/or limited chlorophyll synthesis. The purpling of corn plants could be the result of reduced root development and/or increased anthocyanin production.

Thomison notes that this stage of development generally has little or no effect on later crop performance or yield potential. If it’s induced by environmental conditions, the yellow or purple appearance should change to a healthy green after a few sunny days with temperatures above 70 degrees F (and as soils dry).

If plants remain yellow then closer inspection and assessment is needed to determine if the yellowing is caused by nutrient deficiency or some other factor.

Cooler wet conditions often increase the appearance of these different colors. Some hybrids are more likely to increase anthocyanin (purple pigment) content when plants are cool.

Environmental conditions (high rainfall causing saturated soils) can lead to the appearance of yellow corn. According to Thomison, the visual appearance may be interpreted as N deficiency, but this is rarely the case. Excessive water leads to poor respiration of the roots inhibiting nutrient uptake and affecting cycling of nutrients like nitrogen and sulfur.

This results in the chlorotic appearance which resembles N deficiency. After soils dry out, the appearance returns back to normal. If the chlorotic condition persists after the soil dries, the problem should be investigated further.

This short-term condition should not affect the yield potential of the crop. Potassium deficiency is more likely to show symptoms later in the spring as well.

Thomison also notes that when you combine cool nighttime temperatures, high radiation levels during the day, and wet field conditions, you are likely to start seeing purple plants in some corn fields.

The first thing that may come to mind is a phosphorus deficient soil. This is unlikely the case, especially this early in the year. Phosphorous deficiency should also appear on lower leaves, with upper leaves being of normal coloration.

As a defense mechanism to protect photosynthesis, a corn plant will form pigments to help absorb excess light and divert it away from their photosynthetic centers as a form of sunblock. This purple color is from anthocyanins, which can be formed from excess light or caused by a buildup of sugar (sucrose).

Diverting the excess sunlight protects the photosynthetic mechanism and can reduce the time needed for the plant to recover from excess light stress. Other factors including soil compaction, herbicide injury, etc. can make the effect even more pronounced.

Purple corn can also be the result of what is known as the “fallow syndrome.” If corn follows a fallow season, a root fungus called mycorrhizae reaches a low population. Mycorrhizal infection of corn aids in phosphorus and zinc uptake.

Until the fungal growth is stimulated by the corn roots, which exude starches and sugars, the purple color may persist.

Fortunately, the purple tint is short-lived and rarely persists beyond the V6 growth stage. It should not have an impact on the yield potential of the field.

Another condition I have noticed in some fields as I have been out is “leaning corn.” This is probably due to extreme windy conditions and the excessive rain impacting root development.

Thomison notes it is not uncommon for young plants to exhibit “lodging” as a result of strong winds. We usually see this phenomenon during the V3-V8 stage of development.

He says usually, this leaning is short-lived and plants recover within several days. Sometimes the wind-induced leaning is associated with excessive vegetative growth which gets ahead of the root system supporting the plant, especially when the root system is restricted.

For now, while it is too wet to do anything else, get out into some of your fields and start evaluation your growing crops; watching for insect and disease development.

Don’t forget to start taking inventory of weeds not yet controlled. This will allow you time to develop an effective herbicide program.

Tony Nye is the state coordinator for the Ohio State University Extension Small Farm Program and has been an OSU Extension Educator for agriculture and natural resources for over 30 years, currently serving Clinton County and the Miami Valley EERA.

Tony Nye

OSU Extension