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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter: 2014-35

  1. Does Black Layer Form When Corn Is Frosted?

    Author(s): Peter Thomison

    Black layer is the stage in corn development at which kernel growth ceases and maximum kernel dry weight is achieved (also referred to as “physiological maturity”).  A killing fall frost prior to physiological maturity can cause premature leaf death or whole plant death.  This occurred over the weekend when temperatures dropped below freezing in some late planted Ohio corn that had yet “black-layered”.  The impact of frost injury to immature corn was discussed in the September 23 C.O.R.N. newsletter ( ).  A common misconception is that kernel black layer formation sometimes does not occur following a frost or other late-season severe stress.  Kernel black layer always occurs (Nielsen, 2013).  Any severe stress that occurs during the grain fill period will cause premature kernel black layer formation and is related to the reduction in or termination of sucrose (photosynthate) availability to the developing kernels (Afuakwa et al., 1984).

    Afuakwa, J. J., and R. K. Crookston.  1984.  Using the kernel milkline to visually monitor grain maturity in maize.  Crop Science 24: 687-691.

    Nielsen, R.L. 2013.  Effects of Stress During Grain Filling in Corn.  Corny News Network, Purdue Univ. [online]  [URL accessed Oct. 2014].

    Thomison, P.R. 2014.  Assessing yield losses in corn due to frost.  C.O.R.N. Newsletter 2014 - 32 September 23, 2014 [online]

  2. Soybean Pod Shattering

    Figure A & B. Soybean pods curling after shattering and Soybean harvest losses in 2012 after shatter
    Author(s): Laura Lindsey

    Soybean pod shattering is not completely understood.  Through breeding efforts (beginning approximately 5,000 years ago when soybean was first thought to be domesticated), soybean plants have gained pod shattering resistance (Dong et al., 2014).  However, certain environmental conditions can lead to pod shattering.

    Last week, I received a picture of empty, curled soybean pods which is an indication of shattering loss (top picture).  This particular field received hail which could explain the empty pods.  With the recent wet weather, shattering can also occur as a result of the re-wetting of dry pods.  We saw soybean pods shatter in 2012 when pods were formed under drought conditions and re-wet later in the season.

    Shattering (and other harvest losses) can account for significant yield loss.  In the bottom picture, there are approximately 8 to 12 seeds per square foot which translates into a 2 to 3 bushel per acre yield loss.

    Reference:  Dong, Y., X. Yang, J. Liu, and Y. Wang.  2014.  Pod shattering resistance associated with domestication is mediated by a NAC gene in soybean.  Nature Communications 5:1-11.

  3. Frosted Forage Precautions

    Author(s): Mark Sulc

    Jack Frost will be visiting us soon.  Several forage species can be extremely toxic soon after a frost because they contain compounds called cyanogenic glucosides that are converted quickly to prussic acid (i.e. hydrogen cyanide) in freeze-damaged plant tissues.  We will discuss those first below.  Others species have an increased risk of causing bloat when grazed after a frost, we will discuss those at the end of this article.

    Species that can develop toxic levels of prussic acid after frost include annual grasses in the sorghum family, Johnsongrass, shattercane, chokecherry, black cherry, indiangrass, and elderberry.  It is always a good idea to check areas where wild cherry trees grow after a storm and pick up and discard any fallen limbs to prevent animals from grazing on the leaves and twigs.

    The potential toxicity after frost varies by species as follows:

    *  Sudangrass varieties = low to intermediate in cyanide poisoning potential

    *  Sudangrass hybrids = intermediate potential

    *  Sorghum-sudangrass hybrids and forage sorghums = intermediate to high

    *  Grain sorghum = high to very high

    *  Piper sudangrass = low prussic acid poisoning potential

    *  Pearl millet and foxtail millet = rarely cause toxicity

    Animals can die within minutes if they consume forage with high concentrations of prussic acid.  Prussic acid interferes with oxygen transfer in the blood stream of the animal, causing it to die of asphyxiation.  Before death, symptoms include excess salivation, difficult breathing, staggering, convulsions, and collapse.

    Ruminants are more susceptible to prussic acid poisoning than horses or swine because cud chewing and rumen bacteria help release the cyanide from plant tissue.

    Plants growing under high nitrogen levels or in soils deficient in phosphorus or potassium will be more likely to have high prussic acid poisoning potential.  After frost damage, cyanide levels will likely be higher in fresh forage as compared with silage or hay.  This is because cyanide is a gas and dissipates as the forage is wilted and dried for making silage or dry hay.

    Young, rapidly growing plants of species that contain cyanogenic glucosides will have the highest levels of prussic acid.  After a frost, cyanide is more concentrated in young leaves and tillers than in older leaves or stems.  New growth of sorghum species following a non-killing frost is dangerously high in cyanide.  Pure stands of indiangrass can have lethal levels of cyanide if they are grazed when the plants are less than 8 inches tall.


    Grazing Precautions

    The following guidelines will help you avoid danger to your livestock this fall when feeding species with prussic acid poisoning potential:

    *  Do not graze on nights when frost is likely.  High levels of toxic compounds are produced within hours after a frost, even if it was a light frost.

    *  Do not graze after a killing frost until plants are dry, which usually takes 5 to 7 days.

    *  After a non-killing frost, do not allow animals to graze for two weeks because the plants usually contain high concentrations of toxic compounds.

    *  New growth may appear at the base of the plant after a non-killing frost. If this occurs, wait for a hard, killing freeze, then wait another 10 to 14 days before grazing the new growth.

    *  Don’t allow hungry or stressed animals to graze young growth of species with prussic acid potential.

    *  Graze or greenchop sudangrass only after it is 15 to 18 inches tall.  Sorghum-sudangrass should be 24 to 30 inches tall before grazing.  Never graze immature growth or short regrowth following a harvest or grazing (at any time of the year).

    *  Do not graze wilted plants or plants with young tillers.

    *  Green-chopping the frost-damaged plants will lower the risk compared with grazing directly, because animals are less likely to selectively graze damaged tissue.  However, the forage can still be toxic, so feed greenchop with great caution after a frost.

    *  Always feed greenchopped forage of species containing cyanogenic glucosides within a few hours, and don’t leave greenchopped forage in wagons or feedbunks overnight.


    Hay and silage are safer

    Prussic acid content in the plant decreases dramatically during the hay drying process and the forage should be safe once baled as dry hay.  The forage can be mowed any time after a frost if you are making hay.  It is very rare for dry hay to contain toxic levels of prussic acid.  However, if the hay was not properly cured and dried before baling, it should be tested for prussic acid content before feeding to livestock.

    Forage with prussic acid potential that is stored as silage is generally safe to feed.  To be extra cautious, wait 5 to 7 days after a frost before chopping for silage.  If the plants appear to be drying down quickly after a killing frost, it is safe to ensile sooner.

    Delay feeding silage for 8 weeks after ensiling.  If the forage likely contained high levels of cyanide at the time of chopping, hazardous levels of cyanide might remain and the silage should be analyzed before feeding.

    Freezing also slows down metabolism in all plants that might result in nitrate accumulation in plants that are still growing, especially grasses like oats, millet, and sudangrass.  This build-up usually isn't hazardous to grazing animals, but green chop or hay cut right after a freeze can be more dangerous.


    Species That Can Cause Bloat

    Forage legumes such as alfalfa and clovers have an increased risk of bloat when grazed one or two days after a hard frost.  The bloat risk is highest when grazing pure legume stands, and least when grazing stands having mostly grass.

    The safest management is to wait a few days after a killing frost before grazing pure legume stands - wait until the forage begins to dry from the frost damage.  It is also a good idea to make sure animals have some dry hay before being introduced to lush fall pastures that contain significant amounts of legumes.  You can also swath your legume-rich pasture ahead of grazing and let animals graze dry hay in the swath.  Bloat protectants like poloxalene can be fed as blocks or mixed with grain.  While this an expensive supplement, it does work well when animals eat a uniform amount each day.

  4. Prussic Acid Testing in Forages

    Author(s): Mark Sulc

    Some forage species can develop prussic acid poisoning potential when harmed by frost and management practices should be followed to prevent poisoning of livestock (see accompanying article).  If doubt remains regarding the safety of the forage, it can be tested for prussic acid (cyanide) content.

    Keep in mind that prussic acid is a gas, so it is difficult to detect in samples sent to labs.  Sample handling is extremely critical to ensure that the lab test will be representative of what is being fed to livestock and that the prussic acid did not volatilize during shipment.

    Obtain a representative FRESH sample of the forage to be fed.  Collect 1 to 2 lbs of fresh forage from across the field to be grazed.  For silage, follow proper sampling protocol to obtain a representative sample.

    Do not allow the sample to dry.  Place in an air-tight plastic bag, freeze the sample quickly, and ship to the lab the fastest way (overnight express) in a cooler with an ice pack.

    Remember, cyanide content dissipates with drying of the sample.  So if the sample arrives at the lab drier than the fresh forage that is fed, a false negative result will likely occur.

    The following are two labs that will analyze samples for prussic acid (cyanide).  Other labs may provide testing for prussic acid, always call ahead to confirm whether the prussic acid test is provided and to ask them about their recommended sample handling protocols.


    The Michigan State UniversityAnimal Health laboratory

    DiagnosticCenter for Population and Animal Health


    4125 Beaumont Road

    Lansing, MI48910-8104

    TEL (517) 353-1683, FAX (517) 353-5096

    Request Procedure 70022


    Cumberland Valley Analytical Services, Inc.

    14515 Industry Drive

    Hagerstown, MD21742

    TEL: 1-800-282-7522, FAX (301) 790-1981

  5. Five Things to Know about Fall Herbicide Treatments

    Author(s): Mark Loux

    There is plenty of information on fall herbicide treatments in the C.O.R.N. newsletter archive and on other university websites.  Our philosophy on this has not changed much over the past decade.  A few brief reminders follow:

    1.  When to spray?  Anytime between now and Thanksgiving will work, and possibly later.  We have applied into late December and still eventually controlled the weeds present at time of application.  Once hard freezes start to occur, there is usually a substantial change in the condition of certain weeds, such as dandelion and thistle, that renders them less sensitive to herbicides.  We discourage applications during periods of very cold weather which can occur starting about Thanksgiving, and also (obviously) when the ground is snow-covered.

    2.  What about all of that trash, er I mean crop residue, on the ground after harvest - won’t that cause problems?  We have not worried about this, and the herbicides seem to work regardless.  Most dealers I have asked seem to have the same impression.  On the other hand, it probably wouldn’t hurt to wait a while after harvest to let the residue settle down, and the weeds to poke through.  Dense crop residue usually prevents marestail from emerging anyway.

    3.  Don’t make it too complicated or pricey.  Keep in mind that the primary goal is control of weeds that have already emerged.  This is hard to accomplish with a single herbicide, but there are a number of relatively low cost two-way mixtures that easily achieve this goal.  Our philosophy has generally been to start with 2,4-D, and then add another herbicide that results in more comprehensive control.  Herbicides that make the most sense to add to 2,4-D based on our research:  glyphosate, dicamba, metribuzin, simazine, Basis (and generic equivalents), Express (and generic equivalents), Canopy/Cloak DF or EX, or Autumn Super.  These allow either corn or soybeans to be planted the following year with these exceptions:  simazine - corn next year; Canopy/Cloak - soybeans next year; Basis - possibly restricted to corn based on rate and geography.  We do not see the need for three-way mixtures, although a case can be made to add a low rate of glyphosate to a two-way mix to control grass or improve activity on perennials.  A two-way mixture of glyphosate and Sharpen could also be used, but we believe Sharpen has more utility in marestail control programs when used in the spring.

    4.  Is there an advantage to including residual herbicides?  No, because almost all of them peter out over the winter and fail to provide any control of spring-emerging weeds.  Want a more scientific description of the process than “peter out”?  Ok - a combination of herbicide degradation and dilution and off-site movement occurs that results in inadequate concentrations of herbicide remaining in spring to control emerging weeds.  The primary exception to this is chlorimuron (Canopy/Cloak), which for whatever reason does persist at high enough concentrations to provide some control in spring.  Our research has repeatedly shown that applying other residual herbicides in the fall to get control in spring is a waste of money.  The good news here is that any effective fall herbicide treatment with or without residual will result in a weed-free seedbed in spring, usually into April, so that the spring-applied burndown/residual treatment just has to control small weeds that emerge in the few weeks prior to planting.  That is the goal.

    5.  It doesn’t take a lot of herbicide to control weeds in fall, just the right ones.  There is a tendency for some manufacturers to promote an expensive mixture of too many herbicides that just isn’t necessary.  Avoid most residual herbicides, and also those that mainly “speed up the kill”.  Consider that fall treatments should comprise not more than about 25% of your total herbicide budget for a crop, and it can be accomplished for even less than that.

  6. Ohio Weather Outlook


    The pattern discussed last week will continue this week.  Expect an active weather pattern as a storm system crosses Ohio Tuesday with lingering light showers Wednesday and Thursday keeping field work at a minimum this week. Drier weather will return by the weekend and much of next week outside of some rain maybe on this coming Monday.

    Temperatures will be on a typical roller coast ride starting the week warm then cooler before warmer later next week.  Overall, October will end up being a bit cooler and wetter than normal.  November looks to start warmer than normal temperatures and normal rainfall.  Frost and freeze risk...close to normal.  Risk of frosts and freezes increases next about October 21-23, 2014.

    Wind risk...low, EXCEPT moderate on Tuesday, but most winds Tuesday below 35 mph.

    Rain risk...normal into early November about 1 - 2 inches.  See the latest National Weather Service Ohio River Forecast Center 16-day rainfall outlook at:

  7. 2nd Edition Cover Crops Guide Released - Options To Explore Valuable Cover Crops Information

    Author(s): Sarah Noggle

    Farmers interested in planting cover crops to improve soil health now have two resources available to utilize.  The two items are an expanded and updated second edition of the Midwest Cover Crops Field Guide and also the Midwest Cover Crops Council cover crops selector tool. 

    The second edition of the pocket guide was release on Monday, September 22, 2014 and was produced by the Midwest Cover Crops Council and published via Purdue University.

    Growers plant cover crops for a variety of reasons and possible benefits.  Cover crops can trap nitrogen left in the soil after cash-crop harvest, scavenging the nitrogen to build soil organic matter and recycling some nitrogen for later crop use.  They also can prevent erosion, improve soil physical and biological characteristics, suppress weeds, improve water quality and conserve soil moisture by providing surface mulch.

    The first cover crops guide was released in February 2012.  The updated guide is in response to the increasing interest in cover crops in the Midwest and to requests for additional information.  This new information will help farmers better choose appropriate cover crops for their situation and better manage the cover crops they grow. 

    The updated guide features seven new topics:  Getting started in cover crops; Rationale for fitting cover crops into different cropping systems; Suggested cover crops for common rotations; Cover crop effects on cash crop yields; Climate considerations including winter hardiness and water use; Adapting seeding rates and spring management based on weather; and "Up and coming" cover crops.

    There also is more information about herbicide carryover, manure and bio solids applications, and crop insurance issues.

    Four states have been added to the new guide to round out information for cover crops in the Midwest. They are Kansas, Missouri, Nebraska and South Dakota.

    The guide's second edition is available at Purdue Extension's The Education Store at: .  Search by the name of the publication or product code ID-433.  Writers in the publication are from The Ohio State University Extension, Purdue University and Michigan State University.    

    Also available from the Midwest Cover Crops Council is the Cover Crops Decision Tool.  The MCCC Cover Crops Decision tool is a web-based system to assist farmers in selecting cover crops to include in field crop and vegetable crop rotations.  The web based tool allows users to choose specific state and county locations, along with crop rotation information, soil type, drainage class and top factors the farmer is looking for to determine suitable cover crops for each specific location.  The tool narrows down potential cover crop options and the benefits received from each specific cover crop.  A report is created with considerations for using the cover crop in a specific location, planting information, termination dates, performance/roles, cultural traits, potential advantages and disadvantages and finally information resources about the cover crop. 

    The following link:  will take you to the web based Midwest Cover Crops Council (MCCC) Cover Crops Decision Tool.

  8. Soil Testing and Nutrient Application Practices of Ohio Agronomy Retailers

    A survey of agricultural retailers was undertaken to provide a benchmark of current practice adoption of soil sampling, type of spatial sampling, placement and timing of nutrient application currently being used in Ohio’s two major watersheds. The responding retailers provided services on 3.8 million acres representing 39% of Ohio’s row crop and hay production acres with 1,920,450 in Lake Erie Watershed while 1,910,050 acres were in the Ohio River Watershed. Eighty two percent of the soil sampled was done according to methods that meet or exceed university recommendations.  The Lake Erie Acreage Weighted Average (AWA) reported 74 % and the Ohio River AWA 90% of the acreage being soil sampled according to methods that meet or exceed recommendations (Figure 1). Farmers in the Lake Erie basin are more likely to surface broadcast phosphorus with no tillage done (36%) than those in the Ohio River basin (23%). Incorporation with a planter as starter fertilizer accounts for 30-33% of the applied phosphorus regardless of geography (Figure 2). For all of Ohio AWA most fertilizer is applied in the Fall (September –November) and Spring (March-May) accounting for 77% of phosphorus application. The two watersheds are similar in the Fall application but the Winter period application is higher, 21% in the Ohio River Watershed than 8% in Lake Erie Watershed. Spring application is lower in the Ohio River Watershed at 27% compared to 41% in the Lake Erie watershed (Figure 3).

    A complete copy of the report with more detail can be downloaded at

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.


Amanda Douridas, CCA (Educator, Agriculture and Natural Resources)
Eric Richer, CCA (Field Specialist, Farm Management)
Glen Arnold, CCA (Field Specialist, Manure Nutrient Management )
Les Ober, CCA (Educator, Agriculture and Natural Resources)
Mark Badertscher (Educator, Agriculture and Natural Resources)
Pierce Paul (State Specialist, Corn and Wheat Diseases)
Sam Custer (Educator, Agriculture and Natural Resources)


The information presented here, along with any trade names used, is supplied with the understanding that no discrimination is intended and no endorsement is made by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

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