Winter Questions  01/18/18 10:19:40 AM

Winter offers  time for questions and answers to develop a plan for the coming season.  We have a had some questions regarding the following--
Remember the Japanese Beetles??  More than likely you would rather forget the infestations from last summer.  Yes, they caused a lot of vegetative loss to the leaves of trees and other landscape, but they also caused vegetative loss to corn and soybeans—primarily around the edges of the fields.  It did not appear that any of the infestations in row crop caused any noticeable yield loss.  BUT, what about this coming season? All those beetles laid a bunch of eggs for hatch in 2018.   This could affect my corn stand-- Should I/Can I do something? HELP!!
Japanese beetles spend about 10 months of the year in the ground in the larval stage.  Spring weather mostly dictates the survival rate of all over-wintering insects.  Cold, open winters have a tendency to increase the mortality. Winters with a lot of deep snow packs usually increase the survival rate due to the “insulating affect” of the snow to the overwintering larvae. BUT, that can be tempered with cooler, wetter springs that can promote added soil bacterial influence which in turn increases larval mortality. 
Consider this: 
Think about the number of years in recent memory when corn stand establishment and loss was high due to any specie of grub feeding.  I can think of two in the last 25 years in Eastern Nebraska.  In those circumstances, these areas were along waterways and high residue situations where many overwintering insects call home. These areas were not very big and did not affect more than a acre or two.  IF you are able to apply an in-furrow insecticide, that is certainly an option for control.  There is no seed trait that I am aware of that has grubs of any kind listed for control by using the trait.  Seed treatments (there are many) with insecticide capabilities usually work for some period of time, but can run out of residual if there is a pro-longed window of active grub feeding.
SO, if you are concerned about white grubs or Japanese Beetle larvae feeding, this is not normally something I would consider budgeting for as an expense.  Even in big grub years, their impact on production is historically minimal.
What is soil pH and buffer pH?
We have talked before about the importance of soil pH and insuring that your soil pH is at a level to promote active nutrient uptake.  You really can have an abundance of fertility, but if your soil pH is too low (normally the problem) or too high (it does happen in spots) the corn or soybeans are unable to absorb the nutrition and maintain active and vigorous growth..  The definition of pH is the negative logarithm of the hydrogen ion concentration (nothing is ever easy in chemistry!!).  Hydrogen (H+) and hydroxyl (OH-) ions are responsible for acidity and alkalinity, so in this case it is a measure of soil acidity or alkalinity.  The pH scale goes from 1 to 14.  A soil pH of 7 is considered neutral.  pH's less than 7 are considered acidic and contain higher concentrations of H+ ions. Here is the “electric” part.  Nitrate (NO3-), the most plant available form of nitrogen, and is negatively charged.  Much of the reason that it is so soil mobile, especially in light organic matter/course textured soils, is due to the soil organic matter and the nitrate being unable to form a tight bond.  The more acid the soil, the tightly that bond becomes and the more difficult it is for that bond to break and the nitrate to be available for the plants to absorb it..  The nitrate may still be there to some degree, but it is being held tightly in the soil organic matter due to the acidity of the soil. 
Soil pH's more than 7 are considered alkaline.  They contain more hydroxyl ions (OH-) than hydrogen ions. Since pH is expressed on a logarithmic scale, the concentrations of hydrogen and hydroxyl ions changes TENFOLD for every one unit change in pH. So a soil with a pH of 5 is ten times more acidic than a soil with a pH of  6. Typical soil pHs range from 4 which is extremely acid to 8 which is alkaline.
Hydrogen ions are found in the soil solution as well as bound on exchange sites on clay or organic matter. The concentration of H+ ions in solution is small relative to the hydrogen ions adsorbed on clay and organic matter.  The H+ in solution is called the ACTIVE acidity and is measured by a soil pH test.  The H+ adsorbed to cation exchange sites can be a large reservoir of potential or RESERVE acidity that replaces H+ in solution as they are neutralized by lime.  This resistance of the soil to change pH is called buffering.  In order to determine how much lime is needed to raise the pH, the soil must be tested for this potential or reserve acidity.  This test is called the BUFFER pH.  So, soil pH is a measure of active acidity and buffer pH is a measure of reserve acidity.  Both measures are used to determine liming amounts for acid soils. 
Agronomically we worry most about soil pH and it’s affect on available soil fertility when the soil pH goes lower than 6.0.  Normally when the soil pH goes to that level, your buffer pH is high and it will take a little more time, material, and effort to bring you pH back up to productive crop producing levels.
What about high pH?
Usually not a hot topic at the coffee pot, however, in some of our river bottom areas, high soil pH can be as big of an issue as low pH.  If you have a high soil pH, it is likely a bigger problem, then low levels due to the limited and cost effective measures available to bring the soil pH down.  Living with a slightly alkaline soil (pH 7.0 to 8.0) is much easier and less expensive than trying to lower soil pH.  Planting soybeans with a good iron chlorosis scores will benefit you when your pH crawls above 7… If you are plaqued with high pH—above 8.0 pH—planting corn on these areas usually is a better crop/cost fit than planting soybeans.  Here is why:
A major problem in alkaline soils is reduced nutrient, and especially micronutrient, availability. Iron deficiency (iron chlorosis) is a very common problem in these soils and is the direct result of high pH soils reducing the availability of iron to plants. The most common symptom of iron deficiency is interveinal chlorosis, where leaves turn light green or yellow but leaf veins remain green    Alkaline soils in the Western U.S. contain large amounts of naturally-occurring lime. This “free lime” buffers pH in the alkaline range and makes it extremely difficult to change soil pH.  Irrigation waters/high water table areas can also be alkaline and promote high soil pH. Selecting crops that tolerate high soil pH conditions will insure success in plantings and few problems with iron or other nutrient deficiencies.
LOWERING SOIL PH If soil pH is above 8.0, some action may be needed to reduce pH. After determining soil pH, consider the following measures to lower the pH of highly alkaline soils:
Add elemental sulfur--Elemental sulfur slowly oxidizes in soil to form sulfuric acid. Test the soil occasionally and stop adding sulfur when pH is back to around 7 or below.
Use acidifying fertilizers such as ammonium sulfate.  Another reason corn is usually a better fit in these situations.  Normally we don’t use much fertility type amendments in soybean production.  In corn there are some options. 
What about Gypsum?  Will it help?
Yes, and No.  Gypsum is hydrated calcium sulfate, CaSO4·2H2O, It can be a soil amendment but normally is cost prohibitive.   It is used to make chalk, plaster of paris and drywall for building construction.  Gypsum is added to heavy clay soil to improve its ability to drain and to improve its texture. Gypsum makes clay soils less compact and hard and better able to accept air and nutrients that plants need.  Gypsum is not acid soluble and will not change the soil pH.  Gypsum helps to shift the Ca and Mg levels in soil and offers a readily available form of sulfate sulfur, a valuable secondary nutrient that benefits the soil and crop. The sulfate in gypsum binds with excess Mg in the soil to form soluble Epsom salt, which moves lower into the soil profile. This Mg is replaced by Ca, improving water holding capacity, root development and soil quality.1 It is normally not useful to amend any soil type other than heavy clay.

1Chen, Liming, David Kost, and Warren A. Dick. “Gypsum as an Agricultural Amendment.” The Ohio State University Extension Bulletin 945 (2011). pp. 1464-1470.


Concerns with volunteer corn in corn and/or soybean fields may be more than normal in 2018 because of late harvest, storms, and lodging that occurred in many areas during the 2017. Controlling volunteer corn in corn on corn rotations is not easy.  In soybeans there are certainly more options.  However, understanding the competitive effects of volunteer corn plants on yield can help in making control decisions in corn and soybeans..
 
There is some Corn of Corn Acres in our area and research testing has shown that corn yields can be reduced when volunteer corn populations are high. Low volunteer populations may initially look bad but generally does not impact yield. Volunteer corn is usually not even a cosmetic problem for very long because field corn quickly outgrows it. A study conducted by the University of Illinois in 2005 showed that corn yield was significantly decreased when the density of volunteer corn was over 15,000 plants per acre. In University of Minnesota testing conducted in 2007 at two locations, the average population of volunteers had to be over 10,926 and 8,377 plants per acre to impact corn yield. The data from multiple University testing conducted in 2007 ( really the last BIG Lodging year)  was used to predict the impact of volunteer corn plant populations on corn yield. Predictions indicated that a volunteer population of 1,000 plants per acre would result in less than a 1% loss in corn yield (average of 1 Bu/A in the testing). A volunteer corn population of around 1,000 plants per acre would be considered low but more typical of what a grower would observe in a corn field.
 
How High is High?  A high volunteer populations of 5,000 to 10,000 plants per acre (1 to 2 plants per square yard) can have a predicted yield loss of up to 6%, and a very high population of 20,000 plants per acre had a predicted yield loss of about 12%. Predictions indicate that control measures would be warranted under high volunteer corn populations of around 1 to 2 plants per square yard.
 
The distribution and density of volunteer corn plants can be highly variable in a field. Volunteers can emerge as single plants usually due to kernel loss from the combine, or in clumps resulting from dropped ears or lodging. Testing has shown that volunteer corn plants in ear clumps can be less competitive than the same number of evenly dispersed volunteers.
Volunteer corn plants generally have delayed emergence, reduced vigor, and are usually behind in growth stage compared
 
Volunteer corn plants generally have delayed emergence, reduced vigor, and are usually behind in growth stage development when compared to a “planted” corn crop. Volunteer plants may produce a small ear, but mostly no ear at all by harvest. At the populations and distributions that typically occur in corn fields, volunteer corn is generally not an economic problem.
 
BUT
 
Volunteer corn should be controlled early in corn to help reduce negative impact on yield. Disking/Tillage of volunteer corn in the spring was traditionally the only control option available in field corn.  If you believe there will be a high volunteer corn pressure, your best decision may be to rotate to soybeans and control the volunteers. It is much easier to control volunteer corn with herbicides in soybeans.
 
Volunteer corn is generally less of a problem in no-till fields. No-till leaves dropped ears and kernels on the surface exposed to freezing and thawing, wildlife foraging of the seed, and poor soil contact for germination. Early fall tillage can/did stimulate germination and emergence of volunteer corn prior to a winter freeze, thus reducing the potential amount of emergence this spring. If we get an early spring to promote early volunteer corn growth prior to planting of any crop, tillage is certainly an option not only for the volunteer corn control, but also, any winter annual weed pressure that may have developed. 

 
 
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