By Ryan Klamfoth, Pioneer Field Agronomist
The excitement of harvest is upon us. The view from the combine will provide a front row seat to assess the impacts of the growing season with frequent glances at the yield monitor. The 2023 corn crop has experienced a unique combination of challenges including: low accumulation of growing degree units (GDUs), stretches with no rainfall, plant health issues from diseases such as tar spot, crown rot, anthracnose top die-back, times when low soil moisture limited nutrient uptake, and premature plant death. Recognizing the impact of these challenges is an important step toward better understanding the cause for variable performance that can be expected this year from field to field or even within the same combine pass.
Average heat unit accumulation in many areas of Ohio has been tracking about 5 calendar days behind the 30-year average and 14 days behind the 2022 season. A cool summer has many farmers concerned about shelling wet corn. Despite this year’s lagging GDU accumulation from planting through September, corn fields are visibly changing as plant health deteriorates rapidly. Areas of fields that lose staygreen prior to blacklayer will often have lower harvest moisture, reduced test weight, poor stalk quality, and reduced yield compared to areas with excellent plant health. Healthier plants are able to oppose growing stresses and, as a result, extend grainfill. It should be expected that corn hybrids with superior plant health, staygreen, and leaf retention will delay black layer formation. Slower maturation is often accompanied with higher harvest moisture while, in-turn, providing opportunity for increased yield, higher test weight, and improved stalk quality/late-season standability.
A large portion of Ohio received minimal rainfall (<1.5”) during September. Severe drought stress during the dough (R4) and dent (R5) stages of grain fill decreases grain yield primarily due to decreased kernel weights and is often caused by premature black layer formation in the kernels. Some fields appeared to “burn up” due to drought, other fields prematurely turned because of tar spot pressure, while others appeared nitrogen deficient. The lack of soil moisture inhibited nutrient uptake thus resulting in significant yellowing, leaf cannibalization, and ultimately premature death (PMD). Regardless of the cause, PMD produces the same results — a shortened grainfill period that reduces yield potential, lowers test weight, and weakens stalk quality. Physical characteristics of corn kernels can also provide evidence of PMD. If you examine the back of a kernel (the bottom side as it is attached to the ear) it should be flat or slightly convex in shape. Kernels that have sunken areas or a concave shape indicate that grainfill was ended prematurely. Additionally, lower in test weight grain has a very pale color as compared to grain that “finishes” naturally.
Agronomic stresses from the year may also be found in plant-to-plant variability. Variation in ear height, stalk diameter, and ear size are strong indicators of uneven emergence. Uneven plant growth and variable emergence this spring was common for some planting dates as a result of uneven soil temperature and unequal soil moisture surrounding the seed/seedling. Evidence of cold injury could also be found this spring. Cold injury in corn commonly occurs with water imbibition below 50 degrees F but it is less known that similar abnormalities can happen with large temperature swings of >27 F. A plant gap in a corn stand is an obvious sign of cold/freeze injury but may also be displayed in an uneven stand resulting from abnormal/looped mesocotyl formation or poor root development.
In summary, corn yields in most of Ohio this year are estimated to be very good, but there are still agronomic observations that can help with learning how to grow a better crop in the future. For those bragging at the coffee shop about the dryness of their corn, it may be an indication that some potential yield was left behind due to a premature finish. Conversely, those with “wet corn” may take solace that yield was optimized with a healthier plant and a longer growing season. To one degree or another, all corn farmers in Ohio were victims of a cooler growing season and the resulting consequences this year. Wishing you a safe and prosperous harvest season.