Agronomy Zone 16

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• Aaron Ahrenholz (11)
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• Bill Kessinger (6)
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• Tony Lenz (14)
• Mike McKibben (8)
• Keith Niemeier (11)
• Tony Plenggenkuhle (7)
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• Jim Rowley (8)
• Kevin Ryan (11)
• Thom Schreeg (10)
• Brenton Schwab (9)
• Louis Sutton (12)

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One thing that I like about agriculture is the fact that every season is different.  Some are good, some are bad and some just average.  This spring so far has been a complete opposite of last year.  Planting is ahead of schedule and progressing at a rapid pace.  We finally got some rain that was needed in some parts of the region.  This also has offered the opportunity for everyone to get a break and regroup.  This past week the mornings of April 28 and 29 did bring some frost.  Fortunately almost everything that was planted had yet to emerge.  We have some chance of rain predicted for May 1 through the 3rd, but with warmer temperatures. 

Central Michigan currently has approximately 30 percent corn and 10 percent soybeans planted, while southern Michigan is 75 percent corn and 5 percent soybeans.  North central Ohio has about 80 percent of the corn planted and 55 percent of the soybeans.  Northeast Indiana is almost done with corn and approximately 40 percent done on soybeans.

Soil conditions have been excellent.  The only short-term problem we may face is the potential for another frost.

The introduction of Roundup Ready Soybeans finally gave growers the tool to easily control many of the weed species that have caused so many problems in the past.  The task of field scouting is now much less stressful than it once was.  It seems that the only plants that are visible above the soybean canopy are a few stalks of volunteer corn.  With the widespread use of glyphosate-tolerant corn followed by glyphosate-tolerant soybeans, control of these volunteers is a problem. This really is not a problem since they are only scattered through the field and never put on any kind of an ear.  Insects often clip the silks and feed on the pollen, therefore leaving the soybeans alone.  Volunteer corn is not a problem, or is it?

Volunteer corn is on the fast track to becoming the number one weed in soybeans. What is the yield loss from a few volunteer corn plants towering in a soybean field?  Research studies have shown that as few as 2.4 corn plants per 100 feet of row can reduce yields by 10 percent. With current yields and prices that could result in an economic loss of $50 an acre.

Unfortunately, the problem goes beyond competition for water and nutrients.  Corn rootworm has now found a new source of food and shelter in volunteer corn.  Both northern and western corn rootworms have found that volunteer corn roots are a good source of nutrition and a very good place to lay their eggs for the next generation.  One of the big problems in controlling this pest is the fact that it is so adaptable.  The western variant has adapted to lay its eggs in soybean fields, therefore having corn to feed on next year.  Northern corn rootworms have adapted to rotations with extended diapause, where the eggs lay dormant through two winters and one growing season.  Therefore in a corn/soybean rotation the eggs hatch occurs when corn is planted.  

When volunteer corn plants come from rootworm-resistant hybrids, the insecticide Bt is not a full dose.  Unfortunately, when the larvae are exposed to a sub-lethal dose of the insecticide Bt, they can build up resistance.  This will ultimately cause rootworm corn to become ineffective in controlling the pest.

In studies conducted from 2007 through 2008 Christian Krupke, Ph.D., entomologist with Purdue University reported that Bt volunteer corn in soybeans can act as larval hosts for rootworms, and beetles can survive to adulthood.  Krupke is concerned the situation could allow more corn rootworm larvae to overwinter in soybean fields and it could accelerate the evolution of Bt-resistant rootworm populations.

Glyphosate-resistant volunteer corn can be easily controlled by using a herbicide other than glyphosate.   Most grass herbicides, such as Select Max or Fusilade DX can be tank mixed with glyphosate, therefore eliminating an application. 

LibertyLink Soybeans also offer a solution to this problem.  Ignite herbicide will eliminate glyphosate-tolerant volunteer corn, as well as any glyphosate-resistant weeds.  There are currently no known weed species that are resistant to Ignite.  The Liberty Link system is a great, cost effective solution to this problem.

Every year we are seeing more and more weeds that seem to escape herbicide application, especially glyphosate. Are these weeds herbicide resistant, or simply escapes? If they are resistant, how did they get that way and how do we get rid of them?

Whenever we discuss weed resistance management it is best to begin with some definitions:

Herbicide Mode of Action: Herbicide mode of action refers to the biochemical mechanism by which a herbicide causes growth to cease in target weeds. Herbicides can be classified into groups according to their modes of action.

Source: Herbicide Resistance Action Committee

Herbicide Resistance: This is the inherited ability of a plant to survive and reproduce following exposure to a dose of herbicide normally lethal to the wild types. In a plant, resistance may be naturally occurring or induced by such techniques as genetic engineering or selection of variants produced by tissue culture or mutagenesis.

Source: Weed Science Society of America; International Survey of Herbicide Resistant Weeds

Herbicide Tolerance: This is the inherent ability of a species to survive and reproduce after herbicide treatment. This implies that there was no selection or genetic manipulation to make the plant tolerant; it is naturally tolerant.

Source: Weed Science Society of America; International Survey of Herbicide Resistant Weeds

Weed Resistance: Resistance is the naturally occurring inheritable ability of some weed biotypes within a given weed population to survive a herbicide treatment

that would, under normal use conditions, effectively control that weed population. Selection of resistant biotypes may result in control failures.

Source: Herbicide Resistance Action Committee

How does resistance develop? Changes in weed populations in a given field begin when a small number of plants within a species, called a “biotype” have a distinct genetic makeup that allows them to tolerate a particular herbicide application. One common misconception is that herbicides cause a weed species to develop resistance. Herbicides are not known to directly cause genetic mutations in weeds that lead to resistance. These resistant biotypes may already exist in native weed populations. Therefore in applying herbicides with the same mode of action, some of the biotypes survive and reproduce, thus increasing the resistant population.

The cool, wet weather that we have experienced this fall has created ideal conditions for ear molds.  Diplodia and Gibberella ear rots have been found in many fields throughout Northeastern Indiana, Northwest Ohio and Southeast Michigan. We have not seen molds to this extent in many years.  The high incidence of Gibberella especially is of major concern to livestock producers.

The pathogen that causes Gibberella ear rot produces the mycotoxins deoxynivalenol and zearalenone.  These mycotoxins cause problems when present in a livestock feed ration. Deoxynivalenol, also known as DON, and vomitoxin causes livestock, especially swine, to refuse to eat and eventually regurgitate the feed.  Zearalenone will cause fertility and other breeding problems.  The Food and Drug Administration has established advisory levels of these toxins for animals. For example, the maximum DON level for sows is 3-5 ppm.  The level of the mycotoxins can only be verified through a chemical analysis.  This can be done using a test strip or sending a sample to a lab.  When corn is used for ethanol production the process will destroy the mold, however the process will not destroy the mycotoxins, therefore leaving a higher concentration in the DDG’s for feed use.

Gibberella ear rot can be readily identified by observing the ear prior to harvest.  Inspect 10 ears in several different locations in a field.  Look for mold with a slight pink color (see photo). The mold begins at the tip of the ear and progresses toward the base and rarely affects the entire ear.   

Fields with a high incidence of Gibberella should be harvested as early as possible and kept separately when stored.  Also, setting the combine to prevent small light and shriveled kernels from the grain will help reduce the level of contamination.  Grain should be stored at 15% or lower moisture in order to prevent further growth of the fungus.

Ear rots will survive in corn residue.  Therefore, the best strategy for management is to rotate infected fields out of corn or wheat.  Tillage will also help to break down residue and therefore reduce the presence of the fungus.