By Joel Ransom

The end of the growing season for corn is fast approaching. At this point, it appears likely that we will make it to the end of September without a hard killing frost. Moreover, current climate predictions seem to indicate that October and November will be warmer than normal. This is great news for the drying of the corn crop prior to harvest. Though we started the season with concerns about corn not reaching maturity before the first killing frost, for much of the state our concerns are now focused on the lack of moisture determining the end of the effective cropping season.

Get Ready For Low Test Weight Corn, Ear Drop And Lodging

The impacts of drought on a corn crop are more gradual than that of a hard frost (temperatures below 28 degrees). Drought stress begins by reducing photosynthesis as the stoma close and leaves begin to curl. As this stress continues, the lower leaves begin to die and ultimately the entire plant can be killed. During this process, stored carbohydrates and other nutrients are moved from the lower leaves and the stem into the developing kernels. When stored and newly synthesized carbohydrates are not sufficient to support the development of all the kernels in the cob, the uppermost kernels stop growing. Depending on their stage of development, these kernels may be so small that they will be blown out the back of the combine. Those large enough to not be lost during combining will be smaller than normal and have low test weight.

About half of the crop is now in the dent stage. Generally when a crop gets to this stage, we are not overly concerned about the impact of drought stress on yield. However, this year, since the drought stress started well before this stage of development, continued stress has the potential to dramatically impact yield. In fact, 40% of the total kernel weight is yet to be added to kernels in the dent stage. Therefore, even the kernels at the lower end of the cob will likely fail to fully fill and will have low test weight at harvest.

The recent rain brought relief from severe drought stress in much of the state, but for many farms it came too late to have much of an impact on the corn crop. Crops with few or no green leaves will not benefit from these recent rains.

In addition to its impact on yield, drought stress affects stalk quality. Severely stressed crops will be prone to lodging.

Additionally, ear drop can become more problematic in some hybrids after severe drought. Plan to harvest your most severely stressed fields first, and probably sooner than you would normally plan to, in order to minimize losses associated with downed plants or dropped ears.

Ransom is a North Dakota State University Extension agronomist. Source: ND Crop and Pest Report