The corn growing season is reaching an end, but late-season rains can still have an impact on corn grain quality and test weight. Late-season precipitation can increase fungal colonization of corn ears, increase pre-harvesting sprouting, and reduce final test weight and grain quality.
Moldy ears can occur on corn that died prematurely from stress. Corn in this situation usually has high grain moisture content, which favors fungal colonization (Figure 1). In addition, the wet pattern experienced this past week favors the occurrence of moldy ears. Also, corn ears affected by abiotic or biotic (e.g., insect and bird damage) stress are more susceptible to ear molds.
Figure 1. Moldy corn ears. Photos by Eric Adee and Ignacio A. Ciampitti, K-State Research and Extension.
“Exposed ears” are also more susceptible. Exposed ears occur when the ear keeps elongating beyond the end of the husks. The upper part of the ear becomes partially or completely exposed. The combination of heat and drought early this season, followed by an unusually cool and wet pattern, increased the presence of exposed ears (Figure 2). For more information on this topic and other abnormalities in corn ears, check the new K-State Research and Extension i-book at: http://www.agronomy.k-state.edu/extension/crop-production/corn/
Figure 2. “Exposed” corn ears. Photo by Ignacio A. Ciampitti, K-State Research and Extension.
When ears are exposed out of the husks, diverse disease problems are evident. Some of the most common diseases are: diplodia ear rot, aspergillus ear and kernel rot, fusarium ear and kernel rot, gibberella ear rot, and blue eye mold, among several other diseases.
Low test weight
The occurrence of moldy ears can affect test weight in corn, resulting in light-weight and chaffy grain. Other causes of low test weight are: 1) higher grain moisture, 2) abiotic stress conditions (e.g., drought and heat), 3) late-season leaf diseases, and 4) below-normal temperatures during the end of the grain filling, which was not the case this year.
Moldy ears can also impact final grain quality through the production of mycotoxins, potentially affecting quality of the grain as an animal feeding source. It can also cause issues for storage and end-use processing (e.g., starch quality and ethanol).
Pre-harvest sprouting is likely to occur when dry grain (less than 20% moisture content) is re-wetted. This situation is particularly associated with late-season rains, warm temperatures, and upright ears. The main result is a sprouted kernel in the lower section of the corn ear (Figure 3). If this is a large-scale problem throughout the field, grain quality can be compromised and cause problems for storage purposes.
Figure 3. Premature corn kernel sprouting in the lower section of the ear. Photo by Eric Adee, K-State Research and Extension.
For more information about the causes of low test weight and premature corn kernel sprouting, see the following articles by Dr. Robert Nielsen of Purdue University:
In summary, these production issues are occurring now in the field in some cases. One the most effective management practices is to scout fields for these issues and estimate the portion of your field affected by moldy ears or pre-harvest sprouting problems. Timely harvest and pre-screening of corn ears can help mitigate these issues and diminish the economic impact.
Ignacio A. Ciampitti, Crop Production and Cropping Systems Specialist