When Is Yellow A Problem?

A lot of questions this past two weeks about yellow corn.  We have several things going on. 

Here is the latest one, random yellow plants throughout the field without any pattern.  This one is easy.  It is surfactant burn from post emergent glyphosate applications.  The surfactant is what the chemical manufacturers use to carry the active ingredient, in this case glyphosate.  Different manufacturers use different surfactants, not an issue, generally the newer surfactants are safer.  But this year we had the perfect storm for surfactant burn.

A lot of corn was sprayed last week because the week before most sprayers were busy the week before applying fungicides to winter wheat.  And good spraying days have been few and far between the whole season.  This corn was growing rapidly and pushing the upper limit of safety for glyphosate application.  We don't talk about the upper limit very much because glyphosate tolerant corn is hardly ever injured.  We will get some injury though if the cuticle, or skin, of the corn plant is in a delicate condition.  The corn has delicate cuticles this year because it has not been hot and dry.  Corn skin is like human skin.  Expose it to sunshine and dry conditions and it will get tough.  Humid and cloudy weather keeps the skin more delicate.  Sensitive cuticles will react with the surfactant and bleach yellow.  It is a temporary condition which will disappear in a week as new leaves emerge from the whorl and for this reason the yield impact will be negligible.
Some hybrids do not show this flash because their genetic disposition leads them to create thicker cuticles.  It is the same as some humans have fair skin which burns easily and some humans have dark skin which does not burn as quick.  Does this mean much?  Not to a corn plant.  Not much to a human either unless you are very fair skinned and want to stay outside your entire life.

One last comment. The condition that also leads to thin cuticles is very rapid cell growth.  You can see a corn plant growing rapidly by looking at it's leaves.  If you see some twisting and curling, you can be sure is growing out of its shorts, like the plant below.

In the old days we would blame this on the dicamba or Banvel that was used on 100% of the corn crop in the 80's and 90's.  My old buddy Martin Harry would spend weeks holding hands and saying a prayer over corn fields that were a lot worse than this.   

A much more serious yellow can be seen in fields like this one.

This spring gave no room for error.  The trails through this corn were created by manure tankers.  You can even see cultivator trails on other fields.  Man made compaction and natures' compaction produced by pounding rains are showing up all over the place.  Compaction makes corn roots' lives miserable and starves the plant for oxygen.  Nutrient uptake and growth grind to a snails pace.  This is trouble that relects in the bin.

This is not so much compaction, but side hill seepage from a clay knoll.  Often clay knolls leach water out of their sides and the water will cause the corn to turn yellow too.  Same reason, lack of oxygen in the soil. 
The bad news is there is little we can do to make the corn feel better.  The good news is that 11 moths from now we get to try it all over again.