The dry conditions are causing some to see what is known as “floppy” corn (aka rootless corn). Rootless corn is easy to diagnose – simply dig up plants that are not standing erect like they should be, then gently knock off the soil to get a look at the roots. With rootless corn you will see the seminal roots but no, or poorly developed, nodal roots.
The nodal roots are the permanent roots of the corn plant and begin to grow from the coleoptile node approximately ¾ inch below the soil surface when the corn is V1-V2. The roots will grow deeper as long as the meristematic root tip reaches moisture before it desiccates. With current weather conditions being hot and dry for the coming week, this will exacerbate the issue. Already dry soils will warm up much faster than wet soils, and air temperatures of greater than 90oF can result in soil temperatures reaching lethal levels for young developing roots.
The pictures below are from a field in Johnson County and show corn plants lying flat on the ground with no sign of an open seed furrow. The nodal roots have not developed as they should for V4 corn plant. Normally rootless corn is problematic when the seed furrow reopens, and dry conditions prohibit normal root formation. In this particular field, the furrow remained closed; however, the dry weather and soil conditions have prohibited the nodal roots to develop as they should.
Photos. Rootless corn from Johnson County, IA at approximately V4 growth stage (photo credit Ryan Hahn).
Unfortunately, if you have rootless corn there is not much that can be done to alleviate the problem. Sometimes row cultivation with soil tossed around the corn stalks can spur nodal root development and minimize soil water evaporation near the nodal roots. However, if the soil is already dry the fix will be a soaking rain to provide moisture to allow the nodal roots to develop like normal.
Nielsen, R. 2019. “Rootless” or “floppy” corn syndrome. Corny News Network, Purdue University, West Lafayette, IN. https://www.agry.purdue.edu/ext/corn/news/timeless/floppycorn.html
Elmore, R. and L. Abendroth. 2007. Rootless corn syndrome. ICM News, Iowa State University, Ames, IA. https://crops.extension.iastate.edu/encyclopedia/rootless-corn-syndrome