Wednesday, June 15, 2016

How will the Heat, Drought, and Hail affect Critical Corn Growth Stages (V6 and V12)?

Recently, in training, we have been learning about critical growth stages of corn and this is what we have been discussing:

V6 Corn Growth Stage
Most of the corn has just reached or is just past the V6 corn growth stage.  As most know, this is one of the first critical growth stages because the growing point/tassel is above the soil surface. You can actually cut the lower stalk in half and find them. This growth stage is also very, critical because, thanks to the genetics, the kernel rows are being determined.  If you look at the base of the plant, you might see some lower leaves starting to die as well as some tillers. Some hybrids may form more tillers than others.  Lastly, if you dig, you will find nodal roots, which is going to allow for rapid stalk elongation as well as new leaf development every few days!   

What an Agronomist Fears at V6 Growth Stage
As an agronomist, I fear Mother Nature, because the growing point (hail, flooding, frost) can be now injured, since it is above ground.  Hail has also caused some major leaf defoliation at this growth stage in some areas and this could affect the row number, now determined, by the plant.  If hail causes total defoliation, with a healthy growing point, you could be looking at around 50% yield loss.  Without insurance at this point, a replant could be too late, if hail lowered plant populations.  Many have asked if they should apply a fungicide after hail at this growth stage.  IowaState has done research on this subject.  They have concluded that it would be a "flip of a coin", if you gained any yield with fungicide application, so at this point, I would not recommend fungicide.  Sometimes, plants injured by hail could be infected with common smut, but it rarely is an issue.  In addition, with dry conditions, leaf anthracnose will not be an issue. Corn rootworm hatch and feeding has begun (lightning bugs and shed of cottonwood tree are natural indicators). 


Hail injury at V5/V6 growth stage near Rockford, Illinois

V12 Corn Growth Stage
Some areas were able to plant during a very, early planting window at the beginning of April.  If so, these corn hybrids will be quickly approaching the V12 growth stage in the next few weeks.  If you grab the top of the plant and pull, you can count the number of leaves to the tassel.  Depending on the planting date and maturity, we could be looking at VT the first or second week of July.  We know the kernel row is set, but at this critical growth stage, the number of potential kernels and ear size is being determined. It is possible for a new vegetative growth stage to form every few days and if you look towards the base of the plant, you may discover brace roots forming on top of the soil. 

What an Agronomist Fears at V12 Growth Stage:
As an agronomist, I know that environmental stress can affect the number of potential kernels and ear size at the V12 growth stage.  On average, the plant could be utilizing around .25 inches of rain per day and a major amount of nutrients, so if limited, yield could be affected.  If the plant experiences extreme heat and drought, around 3% yield loss could be lost each day.  Defoliation from hail is now more of a concern and, if the stalk and growing point are not affected, complete defoliation could cause up to 80% yield loss.  I am worried about bacterial diseases like Goss's wilt, if hail injury has occured.  Fungicides will not protect against bacterial diseases, but hybrid resistance will manage this disease.  So, in most causes, if the weather remains dry and if no fungal diseases are present, I would not recommend fungicides.  Lastly, we have had some strong storms pass through in the last week.  You can now start to see difference in hybrid root strength or discover that roots are otherwise compromised.  Corn could bounce back, but at this growth stage, it is possible to start seeing some yield loss (2 to 6%) if corn remains lodged.  Weed escapes, especially waterhemp, can be found lurking beneath the canopy, which means competition for moisture, during drought.


Waterhemp escapes could compete for moisture in V9/V10 corn in Sangamon County, Illinois

Reference:  http://corn.agronomy.wisc.edu/Management/L011.aspx

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