Drought at different times of the growing season can have different effects on a growing corn crop. When drought is paired with high heat, yield loss can be devastating. Often, drought stressed corn should be treated differently at harvest.
If a corn plant undergoes extreme drought during vegetative growth, cell expansion is limited, and the corn plant can be short. This can create issues in the fall if the ear set is below the level at which the combine can successfully harvest the ear. Drought during pollination may cause spotty pollination on the ear (Figure 1) and inconsistent ears may prove difficult for combine adjustment. If the drought stress continues into grain fill, test weight can often be negatively affected, and stalk strength compromised as the plant cannibalizes carbohydrates to fill the kernels (Figure 2). Stress during grain fill can also cause ear shanks to become weaker if the shanks do not develop correctly in the stressful droughty growing conditions. If this occurs, there is reason to be concerned as the ears may drop before planned harvest.
Several ear molds are more common during drought conditions including common smut and Aspergillus. Smut does not produce a mycotoxin; however, Aspergillus can - scouting during harvest to understand these issues can help address livestock feed concerns. Drought stressed corn can naturally have higher levels of aflatoxins. Long term storage can increase levels of aflatoxin if the corn is stored above 14 percent moisture content. The grain should be tested for aflatoxin levels and any that tests above 100ppb (parts per billion) should be stored separately and not for long term.
Drought stressed corn plants can have poor stalk strength as the plant takes its carbohydrate sinks from the stalk and gives it to the ear. Timely harvest is critical for drought stressed corn because stalks can be hollow, may be diseased, and can snap with a gentle push. While walking fields to scout for stalk strength, randomly push stalks over into the adjacent row and view for snap back. Make note of the percentage of those breaking to help determine if an early harvest is necessary. There is often stalk rots in corn plants with poor stalk strength; however, the stalk rot is often a secondary issue that comes after the initial stress. If plants start to lodge, harvest can be slowed dramatically; therefore, it may be necessary to harvest at a higher moisture content than desired to help ease harvesting.
In extreme drought cases, one should pay close attention to the economics of running the combine across the field. With exceptionally low potential yields, the cost to run the combine across the field can soar. Assuming a corn grain market value of $5.00 per bushel and a harvest cost of $38.90 per acre (2021 Iowa Farm Custom Survey), it would take an average of 7.78 bushels per acre to pay for a combine pass.1 It is certainly rare to see conditions that extreme. Drought conditions are certainly not desired, but they are a reality and it is important to be prepared to timely harvest the crop and make decisions to help minimize risk during harvest and storage processes.
1Plastina, A., Johanns, A., Gleisner, A., and Qualman, A. (2021) 2021 Iowa farm custom rate survey. FM 1698. File A3-10. Ag Decision Maker. Iowa State University Extension an Outreach. https://www.extension.iastate.edu/agdm/crops/pdf/a3-10.pdf.
Licht, M. and Archontoulis, S. 2017. Influence of drought on corn and soybean. Integrated Crop Management. Iowa State University. https://crops.extension.iastate.edu/cropnews/2017/07/influence-drought-corn-and-soybean.
Brackenrich, J. and Roth, G.W. 2020. Managing stressed corn. PennState Extension. The Pennsylvania State University. https://extension.psu.edu/managing-drought-stressed-corn.
Ciampitti, I., Jardine, D., Shoup, D., and Duncan, S. 2017. Considerations when harvesting drought-stressed corn for grain. Agronomy eUpdates. Kansas State University. https://eupdate.agronomy.ksu.edu/article_new/considerations-when-harvesting-drought-stressed-corn-for-grain-649-3.
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