We have had reports of several visual nutrient deficiency symptoms in corn. First, we need to remember that plants use energy to uptake nutrients, so under cool or wet conditions plants may not uptake some nutrients and may show deficiency symptoms that will go away as soon as conditions improve. If conditions improve and symptoms persist then it is a true deficiency. There are also other conditions that can help us to properly diagnose a deficiency. For instance, if a farmer has been following a sound fertility program, a deficiency should not be expected as nutrient levels do not tend to change dramatically from one season to the next.
Lately, some have asked if the striping we see in corn is magnesium (Mg) deficiency. It may help to know that soil pH affects the availability of Mg to plants. Magnesium deficiencies are more common under acidic than under neutral or alkaline pH. My guess is that most of it is probably low sulfur levels because of all the rain we have received or just an imbalance due to large amounts of N applied at sidedress. In most years it shows around V6-V8 in corn. I am not sure we need to do anything about it, particularly if there is no history of a deficiency. Research in the Midwest has shown inconsistent results under these conditions. In my previous post I talked about how sulfur depositions have decreased through the years and suggested the inclusion of ammonium sulfate as part of a fertility program.
There are symptoms that may look like nutrient deficiencies and could be wrongly diagnosed as such. Below are some examples. When in doubt, take plant samples. Make sure to collect the appropriate plant part as the established reference values change and are based on a specific plant part collected at the particular growth stage.