What to do about yellow corn plants?

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Yellow corn has been a hot topic. Green/yellow corn plants are present within the same row. A distance of green plants is followed with a distance of yellow plants. A green plant is beside a yellow plant.

This situation can be found on most soil types and no-till/conventional-till.

Also field sandier (light-colored, coarse-textured soil) areas have yellow plants while field bottom (dark-colored, finer-textured soil) areas have green plants.

What is the cause and what action should be taken? Primary potential causes (from most likely to less likely) are environmental conditions, sulfur deficiency, nitrogen deficiency, and manganese (not magnesium) deficiency.

Environmental Conditions

Until recent days, corn roots have experienced cool, wet soils. These conditions have resulted in very limited/shallow root systems. Corn poorly functioning root systems are feeding from a very small soil volume. Recent days/nights have been warmer (80s daytime, 60s nighttime) and drier.  Be patient (wait a week) and allow roots to grow laterally/deeper.

Sulfur Deficiency

Remember the wet 2013. Remember 2013/2014 wheat sulfur deficiencies. For light-colored, coarse-textured soils, 20 lbs/acre of sulfur should always be a part of the corn fertility program. If 20 lbs/acre of sulfur was not applied on light-colored, coarse-textured soils, it is needed. If 20 lbs/acre of sulfur was applied on light-colored, coarse-textured soils, consider waiting a week to see if corn roots will find it soon.

Ammonium sulfate and K-Mag/Sul-Po-Mag are two common sulfur sources: 100 lbs/acre of ammonium sulfate will provide 21 lbs/acre of nitrogen and 24 lbs/acre of sulfur; 100 lbs/acre of K-Mag/Sul-Po-Mag will provide 22 lbs/acre of potash, 11 lbs/acre of magnesium, and 23 lbs/acre of sulfur. If leaching rains have occurred since preplant/at-plant nutrient applications, I prefer ammonium sulfate. Ammonium sulfate will ensure shallow sulfur and nitrogen are present for limited/shallow root systems.

Nitrogen Deficiency

Nitrogen deficiency is ranked after sulfur due to 1/3 -1/4 of total corn nitrogen being applied preplant and/or at-plant. Recognize leaching concerns apply to sulfur and nitrogen. Remember the very small soil volume corn roots are currently feeding. For light-colored, coarse-textured soils, consider waiting a week to see if corn roots will find nitrogen soon. If plants do not respond, consider 100 lbs/acre of ammonium sulfate.

Manganese (not Magnesium) Deficiency

Proper soil pH is the nutrient foundation for any crop. For mineral soils, the target pH is 6.0.  Above 6.2, manganese deficiency can be the cause of yellow corn. Swine lagoon sprayfields, past lime pile spots, nearby rock/gravel roadbeds, and field entrances/perimeters are common areas for 6.2+ pHs. This situation will likely require 2 foliar applications of manganese (0.5 lb/acre actual manganese per application) 7-10 days apart.

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