Editor’s note: The following was written by Megan Taylor and Aaron Nygren, University of Nebraska Extension educators, for the university’s Crop Watch website Sept. 3.
Crops continue to mature as we rapidly move towards harvest 2020, however, when scouting you may start to see more ears that have prematurely drooped.
In corn, ears typically remain upright until after they have reached black layer (R6). Once corn reaches physiologic maturity, the shank that supports the ear begins to deteriorate, causing the ear to droop. However, many of our acres currently range in development from dough (R4) to dent (R5), with some fields just entering black layer (R6).
What is causing this phenomenon in our corn? And what does this mean for yield in those fields affected?
early ear decline
There can be several contributing factors that cause early drooping of ears. Drought stress, high temperatures, poor root development, population and genetics can all be players.
Note that if you are raising non Bt trait corn, then insect pressure from European corn borer could also be a possible factor for early ear droop on your acres.
This year throughout the Corn Belt, our environmental conditions were stressful at planting, during pollination and at grain fill. Early on we had cooler soil conditions and corn got off to a slow start. These cooler conditions delayed germination and emergence in some of our corn acres.
As we transitioned into summer the heat really took over, especially during pollination. Then as we moved into grain fill, water became scarce and drought conditions started to affect areas. These combined to create a suite of conditions that could cause ears to droop prematurely.
Currently, it does appear that drought is the main stressor that could have caused these ears to droop earlier than normal. The shank can become weakened due to a loss of turgidity in combination with carbohydrates being cannibalized under drought stress.
High temperatures can further reduce grain filling corn by increasing evapotranspiration, putting more stress on the corn plant.
Root development and function could also play a role, especially under drought conditions. Once the shank bends over, the pinch point restricts the flow of carbohydrates from the plant to the ear. If the flow is completely shut off, grain fill to the ear ceases and the kernels will prematurely reach black layer.
Impact on yield
Timing and scouting will be key to understanding the impact early ear droop will have on yield. Scouting your fields to determine the development stage of the ear when it droops is critical.
It is important to note that at the beginning of dent, corn still has about 30 to 33 days until it reaches full maturity. Kernel moisture is at 60% and kernel dry matter is only 45% of the final at the beginning of dent.
When looking at estimated loss, if the ear droops during early dent when the milk line is hard to differentiate, yield loss could be up to 40% if the flow of carbohydrates is completely shut off. If the ear droops at the end of the dent stage, when the milk line is close to the tip of the kernel, then yield losses could be up to 12%.
To estimate these losses in your field, identify the development stage in which the ear drooped, then you can multiply the percentage of ears affected by the estimated yield loss per ear (depending on the growth stage utilizing the 40% or 12% loss estimations).
Another factor with ears that prematurely drooped is the integrity of the shank. If the shank is weakened, there is an increased risk of the ear dropping to the ground and increasing harvest losses. This can be exaggerated with less than ideal weather conditions.
Ultimately, pre-harvest scouting can help set expectations come harvest time and help to prioritize fields for harvest.