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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2012-32

Dates Covered: 
September 25, 2012 - October 2, 2012
Greg LaBarge

Feeding Cover Crops? – Consider Nitrate Potential

If you have planted cover crops and plan to graze, ensile, or make hay out of them to feed to livestock, you should consider the potential for nitrate toxicity in the forage this year. This could be especially of concern for cover crops planted after corn silage that was stunted by drought and received a good dose of N fertilizer earlier this year. Nitrates can accumulate in about any cover crop, including oat, cereal rye, annual ryegrass, and brassica species. If there is potential for N carryover in fields where you planted cover crops, of if N fertilizer was applied to the cover crop forage, it is advisable to test the forage for nitrate content before you harvest or graze the forage this fall. Recent rains could have promoted a flush of nitrates to be taken up by the plant. To make matters worse, the current cold snap might shut down plant growth (depending on the cover crop species) preventing further accumulation of yield, so high nitrate concentrations will not be diluted out in the plant. So consider the N carryover situation in your fields, and test your cover crop forage accordingly.

Premature Sprouting of Corn Kernels

Premature Sprouting of Corn Kernels

We have received several reports of premature corn kernel sprouting across Ohio. The ear in the picture exhibiting premature kernel sprouting was sampled from one of the Ohio Corn Performance Test plots at the NW Research Station and was associated with a tight husk and an upright orientation.  A combination of factors, including erect ears, bird damage, ear molds, and wet weather, contribute to premature sprouting.  The problem is usually limited within fields but if it’s evident across a field it has the potential to cause drying and storage problems.  Fields showing widespread kernel sprouting should be prioritized for early harvest.

For more detailed discussion of premature kernel sprouting, check out the following newsletter articles from Purdue and Missouri.

Nielsen, Bob. 2012. Premature Corn Kernel Sprouting (aka Vivipary). Corny News Network, Purdue Extension. [online] Available at URL:

Wiebold, Bill. 2009. Wet Weather Can Cause Seeds to Sprout before Harvest. Integrated Pest & Crop Management Newsletter, Univ of Missouri.

Kernel red streak is also present on many of the kernels on the ear in the picture. With this kernel problem, red streaks form on the sides of kernels and extend over the crown; symptoms are most pronounced at the tip of the ear. Kernel red streak is caused by a toxin secreted during feeding by the wheat curl mite. Severity of symptoms varies among hybrids. The streaking develops in the pericarp but does not affect the feed or nutritional value of corn. The reddish discoloration is a cosmetic blemish, and may affect certain uses of food grade corn, and may thereby reduce premiums.

Cover Crops and Soybean Cyst Nematode

Soybean cyst nematode continues to expand in the state, robbing yields from more fields and larger areas within fields.  Where it does occur, SCN has been managed with rotation, rotating non-hosts (corn and wheat) and rotating varieties with SCN resistance.There is one factor that can contribute to this management approach not working and that is the planting or failure to control other hosts of soybean cyst nematode.  Soybean cyst nematode has a broader appetite than just soybean.  There are also regional differences in the host range of some of these populations.  In other words, the SCN in one state might be able to reproduce on one host and not the same in another.  In addition to the weed plants, the following crop plants have been tested with Ohio populations and found to make good hosts:

  • Alsike clover
  • Bird’s-foot trefoil
  • Green beans, dry beans
  • Common and hairy vetch
  • Cowpea
  • Crimson clover
  • Lespedezas
  • Pea
  • White & Yellow Lupine
  • Sweetclovers   

More importantly, almost all legumes have been shown to be a host of some population within the US, even those that are reported to be non-hosts to some populations.  Care should be taken in planting cover crops, these hosts should be rotated as well to avoid the adaptation of SCN populations.  The best tool to know and track your populations is to monitor their abundance in the soil – with the soil test.  If they keep increasing even with the planting of non-hosts – they will have adapted.  When you plant soybeans, the performance is not what it should be – check for SCN with a soil test.

Jack Frost and Forage Toxicity

Jack Frost and Forage Toxicity

Fall is in the air and Jack Frost will strike sooner or later. When he does, questions always arise concerning the dangers of feeding frosted forages. A very few forage species can be extremely toxic soon after a frost.

The warm-season annual grasses in the sorghum family and other closely related species are capable of becoming toxic to livestock after a frost event. Those species contain compounds called cyanogenic glucosides that convert quickly to prussic acid in freeze-damaged plant tissue. Prussic acid is also known as hydrogen cyanide – the very substance of murder mysteries!

The potential toxicity after frost varies by species. Sudangrass varieties are low to intermediate in cyanide poisoning potential, sudangrass hybrids are intermediate, sorghum-sudangrass hybrids and forage sorghums are intermediate to high, and grain sorghum is high to very high and is most likely to be toxic after a frost. Piper sudangrass has low prussic acid poisoning potential. Pearl millet and foxtail millet have very low levels of cyanogenic glucosides and rarely cause toxicity.

Other species that have potential to have toxic levels of prussic acid after frost are Johnsongrass, chokecherry, black cherry, indiangrass, elderberry, and some varieties of birdsfoot trefoil.

Animal symptoms of prussic acid poisoning

Animals can die within minutes if they consume forages such as the sorghum species that contain high concentrations of prussic acid in the plant tissue. The prussic acid is released from the forage and 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.

Factors that increase prussic acid toxicity

Plants growing under high nitrogen levels or in soils deficient in phosphorus or potassium will be more likely to have high cyanide 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 containing cyanogenic glucosides will have the highest levels of prussic acid. After a frost, cyanide is more concentrated in young leaves than in old leaves or stems. New growth of sorghum species following frost is dangerously high in cyanide. When sorghum species regrow after a drought, the new growth is also dangerously high in cyanide. Pure stands of indiangrass (not common in Ohio and nearby regions) 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 the toxic compounds are produced within hours after a 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 18 inches tall. Sorghum-sudangrass should be 30 inches tall before grazing. Never graze immature growth.
  • 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 be less likely to selectively graze damaged tissue. However, the forage can still be toxic, so feed greenchop with great caution after a frost.
  • Feed greenchopped forage within a few hours, and don’t leave greenchopped forage in wagons or feed bunks 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 anytime 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 has undergone silage fermentation 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 within a shorter time period after the frost.

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.

What about frosted alfalfa, clover, and grasses?

Other common forages such as alfalfa, clovers, and cool-season perennial grasses do NOT produce toxic compounds after a frost. There is different concern, however, when grazing alfalfa or clovers after a frost – and that is bloat. One or two days after a hard frost, the risk of bloat is higher for animals grazing legumes. The bloat risk is highest with grazing pure legume stands, and least when grazing stands having mostly grass and only low amounts of legumes present.

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.

Testing for Prussic Acid Content in Forages

An accompanying article describes the species that can develop prussic acid poisoning potential and management practices to follow to prevent poisoning of livestock with those species after a frost. If doubt remains regarding the safety of the forage, the forage can be tested for prussic acid (HCN) content. But 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.

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 the fastest way (overnight express) in a cooler with an ice pack.

Remember, HCN 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 about sample handling protocols.

The Michigan State University Animal Health laboratory

Diagnostic Center for Population and Animal Health

Michigan State University

4125 Beaumont Road

Lansing, MI  48910-8104

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

Request Procedure 70022


Cumberland Valley Analytical Services, Inc.

14515 Industry Drive

Hagerstown, MD 21742

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

Armyworm in Forages

We had a report of an armyworm problem in forages that contain grasses last week that is worth mentioning.  Many livestock producers have planted late summer forages for possible winter feed and obviously do not need their stands lost to this pest.  Growers might want to check their forage stands for signs of late armyworm feeding.  If significant, they might want to consider treatment.  However, remember to read the labels and follow any and all restrictions.

Weather Outlook

The outlook for the next two weeks ending Oct. 7 calls for slightly below normal temperatures and normal to above normal rainfall. The main wet period will be from Tuesday through Friday this week but may linger in the far south and east and northeast into the weekend. Next week looks drier. The southern two-thirds of Ohio will likely see 1-2 and possibly 3 inches of rain. The north and northwest will likely stay at an inch or less.

After some areas of frost on the weekend it looks like a low threat for frost until around Oct. 4th or 5th at the earliest.

The overall pattern looks somewhat active in the next month with few periods of more than 5 days without some rainfall. This is not uncommon coming out of a bad drought summer.

The winter outlook has become more uncertain. A weak El Niño will likely be around this fall but may quickly end this winter. If it does so the warm and drier winter outlook that the official NOAA outlook is calling for will not happen and a wetter and more seasonable temperature pattern will occur. We should get a better handle on this in Oct. and Nov.

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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.