by Dan Quinn

Reports of corn that appeared to die earlier than normal filtered in from certain locations within the Corn Belt. Even though you may already be harvesting, it’s a teachable moment. Look back and understand why this may have happened.

As corn plants progress through grain fill and approach maturity, plant leaves naturally begin to senesce, or die. Leaf senescence in corn is a naturally occurring, whole-plant process where leaves lose their greenness due to a reduction in chlorophyll. It is a function of degradation and the movement of nutrients to the ear and kernels so grain fill can be sustained and completed.

In addition, corn leaf senescence typically begins before all leaf area has developed — even before pollination — and increases during the grain fill period. Previous research has identified both an extended grain fill period and sustained leaf greenness as contributing factors to higher grain yield. This is often referred to as delayed senescence. Therefore, stressful conditions during grain fill that cause accelerations in grain fill, leaf senescence and plant maturity have been attributed to reductions in yield.

Top dieback

One noticeable symptom of plant stress during grain fill is the earlier-than-expected senescence of the upper portion of the plant, or “top dieback” in corn. The pattern of leaf senescence in corn is expected to start at the bottom of the plant and slowly progress toward the canopy. However, this is not always the case. It can vary based on hybrids and environmental conditions.

When these symptoms occur in many different hybrids or across entire fields, show up much earlier than expected during grain fill, and are occurring simultaneously with stressful conditions, this can indicate that grain fill and yield may be impacted.

That’s even more likely if the top four to five leaves are senescing. Common environmental stressors that cause these symptoms include both excessive heat and dry conditions during grain fill. Excessive heat and drought stress can promote and accelerate leaf senescence and plant maturation. They highlight the difficulty of plants attempting to maintain green leaf area with high transpiration demands.

Late-August weather

These symptoms were most noticeable throughout various cornfields following excessive heat and dry conditions in late August. During the week of Aug. 21 in West Lafayette, Ind., air temperature highs averaged 91 degrees F, with a couple of days reaching much higher.

Fields that already had indications of stress, like nitrogen deficiency, heading into these weather conditions showed the most rapid changes in leaf senescence and visual symptoms of top dieback, and were likely impacted the most.

Therefore, assessing plant health, leaf senescence timing and leaf senescence patterns during grain fill can be important when understanding how well, or not so well, your corn yield ended up.

Quinn is a Purdue Extension corn specialist. Email him at [email protected].