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Ohio State University Extension


C.O.R.N. Newsletter 2007-37

Dates Covered: 
October 29, 2007 - November 5, 2007
Curtis E. Young

Frost Damage and Prussic Acid Poisoning Potential

Authors: Mark Sulc

Jack Frost is finally taking his first bites of the year, bringing the potential for prussic acid poisoning when feeding forage from the sorghum family. Those forages contain cyanogenic glucosides, which are converted quickly to prussic acid in freeze-damaged plant tissue. Prussic acid, also known as hydrogen cyanide, can kill animals within minutes if it is present in high concentration.

Prussic acid binds hemoglobin in the bloodstream and interferes with oxygen transfer. The animal basically dies of asphyxiation. Symptoms include excess salivation, difficult breathing, staggering, convulsions, and collapse. Ruminants are more susceptible than horses or swine because cud chewing and rumen bacteria help release the cyanide from plant tissue.

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. Johnsongrass, chokecherry, and black cherry also have potential for prussic acid poisoning. Piper sudangrass has low prussic acid poisoning potential, and pearl millet is virtually free of cyanogenic glucosides.

Plants growing under high nitrogen levels or in soils deficient in phosphorus or potassium will be more likely to have high cyanide potential. After frost damage, cyanide levels will likely be higher in fresh forage as compared with silage or hay, because cyanide is a gas and dissipates as the forage cures and dries.

When grazing or greenchopping sorghum species this fall, follow these guidelines:
* 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 the plants are dry, which is usually 5-7 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 10-14 days before grazing.
* Don't allow hungry or stressed animals to graze young sorghum grass growth.
* Graze or greenchop only when sudangrass exceeds 18 inches in height, and sorghum-sudangrass should be 30 inches in height before grazing. Never graze immature growth at any time.
* 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 have less ability to selectively graze damaged tissue; however, the forage can still be toxic, so feed with great caution. Feed greenchopped forage within a few hours, and don’t leave greenchopped forage in wagons or feedbunks overnight.

When making hay or silage from sorghum species this fall, consider the following:
* Prussic acid content 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. It is very rare for dry hay to contain toxic levels of prussic acid. If the hay was not properly cured, it should be tested for prussic acid content before feeding.
* Forage that has undergone silage fermentation is generally safe to feed. To be extra cautious, wait 5 to 7 days before chopping after the forage was frosted. If the plants appear to be drying down quickly after a killing frost, it can safely be ensiled within a shorter time period from the frost.
* Delay feeding silage for 8 weeks after ensiling. If the forage likely contained high HCN levels at time of chopping, hazardous levels of prussic acid might remain and the silage should be analyzed before feeding.

Other common forages such as alfalfa, clovers, and cool-season perennial grasses do NOT produce toxic compounds after a frost and can be fed safely. The only concern is a slightly higher potential for bloat when grazing legumes within a day or two after a killing frost.

Testing for Prussic Acid Content in Forages

Authors: Mark Sulc

An accompanying article describes the management practices to follow for feeding the sorghum species to livestock 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, 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 as soon as they arrive. Other labs may provide testing for prussic acid, always call ahead to confirm whether the prussic acid test is provided.

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, web site:, Request Procedure 70022, Cost is $24/sample

Midwest Laboratories, 13611 B Street, Omaha, NE 68144-3693, TEL (402) 334-7770, FAX (402) 334-9121, web site:, Cost is $32 per sample, expect 5-working day turn around time

Harvest Delay Impacts Corn Performance

Authors: Peter Thomison, Allen Geyer, Rich Minyo

Harvest delays expose a corn crop to less favorable weather conditions, as well as wildlife damage. Additional losses may occur when ears on lodged plants come in contact with wet soils and surface residues resulting in development of ear rots. Ear rots reduce grain quality and lead to significant dockage when the grain is marketed. Some ear rots produce mycotoxins, which may cause major health problems if fed to livestock.

Several years ago we conducted a study that evaluated effects of four plant populations (24,000, 30,000, 36,000, and 42,000 plants/A) and three harvest dates (early-mid Oct., Nov. and Dec.) on the agronomic performance of four hybrids differing in maturity and stalk quality. The study was conducted at three locations in NW, NE, and SW Ohio over a three year period (2002-2004) for a total of eight experiments. The following lists some of the major findings from this research.


1) Results showed that nearly 90% of the yield loss associated with delayed corn harvest occurred when delays extended beyond mid-November.

2) Higher plant populations resulted in increased grain yields when harvest occurred in early to mid-October. Only when harvest was delayed until mid-November or later did yields decline at plant populations above 30,000/acre.

3) Hybrids with lower stalk strength ratings exhibited greater stalk rot, lodging and yield loss when harvest was delayed. Early harvest of these hybrids eliminated this effect.

4) The greatest increase in stalk rot incidence came between harvest dates in October and November. In contrast, stalk lodging increased most after November.

5) Harvest delays had little or no effect on grain quality characteristics such as oil, protein, starch, and kernel breakage.

6) Delaying harvest until November decreased grain moisture content by 5.8% (from 23.8 to 18.0%). Further harvest delays achieved almost no additional grain drying.

The 2003 and 2004 growing seasons during which most of this research was conducted were extremely favorable for corn growth and yield. Record corn yields were achieved statewide. Due to stress conditions in 2007 in various parts of Ohio, stalk quality is probably inferior to those past two years. In some severely stressed fields, corn died prematurely in August and September and significant stalk deterioration has already occurred. Given the poor quality of corn stalks in many corn fields, it’s likely that we could expect greater stalk lodging with shorter harvest delays than the research above would indicate.

For more details concerning this study, including table summaries, check out - "Effects of Harvest Delays on Yield, Grain Moisture and Stalk Lodging in Corn." C.O.R.N Newsletter 2005-34 (October 10, 2005 - October 18, 2005); available online at:

Fall Slug Sampling

Authors: Ron Hammond, Bruce Eisley

This the time period when fields should scouted for potential slug problems next year. Sampling is easiest following harvest. While we do not have thresholds, sampling will indicate whether a field has a small or large slug population. Fields with large numbers of slugs should be monitored more closely next spring. Fields with low numbers, while still needing sampling next spring, can be a lower priority.

There are various ways you can sample, with the main one done by placing about 10 wood boards or roofing shingles on the ground across the field and checking them by counting the number of adult slugs underneath the traps. It is best to count the slugs in the morning. Other ways of determining if fields have a lot of slugs is by visiting the fields in late evening before dusk or early in the morning during periods of heavy dew or fog for slugs crawling on the plant residue. Growers are also advised to look underneath the leaves of larger weeds that are covering the ground.

Archive Issue Contributors: 

State Specialists: Ann Dorrance, Pierce Paul and Denis Mills (Plant Pathology), Ron Hammond, Andy Michel and Bruce Eisley (Entomology), Mark Sulc (Forage Specialist), and Peter Thomison, Allen Geyer, and Rich Minyo (Corn Production). Extension Educators: Harold Watters (Champaign), Howard Siegrist (Licking), Roger Bender (Shelby), Glen Arnold (Putnam), Wes Haun (Logan), Steve Foster (Darke), Ed Lentz (Seneca), Jonah Johnson (Clark), Todd Mangen (Mercer), Greg LaBarge (Fulton), and Curtis Young (Allen).

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.