As of May 6 2019, 36 percent of Iowa’s corn is planted according to the USDA-NASS. Under cool conditions (50 to 55oF soils), it may take more than three weeks for corn to emerge whereas corn in 70oF soils can emerge in less than a week (Licht et al., 2001). Cool and wet conditions at or around planting delay emergence and provide seedling disease pathogens, like Pythium, a favorable environment and longer time to infect corn seeds or seedlings (Munkvold and White, 2016; Robertson and Munkvold, 2007). The cool and wet conditions could also result in herbicide injury due to the slow growth and prolonged exposure to herbicides. Additionally, for corn planted shortly before (24 to 36 hours) the cold spell over the weekend of April 27 and 28, imbibitional chilling may be a concern. Corn planted ahead of the cold spell could still experience cold injury, which causes abnormal shoot growth like twisting or problems with root system development.
Iowa State University
Vittetoe, Rebecca K. and Anderson, Meaghan J. B., "Evaluating Corn Stands" (2019). Integrated Crop Management News. 2539.
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