Johnsongrass

Latin Name: Sorghum halepense

Identifying Characteristics:

  • Grows up to 6 ft tall
  • Triangular panicle seedhead
  • White mid-vein
  • Jagged membranous ligule
  • Strong rhizome system

Plant Longevity:

  • Perennial warm-season-grass

Where Commonly Found:

  • Pastures
  • Fence rows
  • Ditch banks
  • Roadsides

Time of Most Concern:

  • Hydrogen cyanide toxicity
    • When the plant or tillers of a plant are less than 24 inches tall
    • After a hard frost in fall
  • Nitrate toxicity
    • During drought
    • High nitrogen application
    • Uptake of nitrate into plant after a rain that follows drought

Compound that Causes Concern:

  • Hydrogen cyanide, also commonly called prussic acid
  • Nitrate

Part of Plant Most Toxic:

  • Hydrogen cyanide
    • Young tillers
    • Immature leaf tissue
  • Nitrate toxicity
    • Lower stem

Livestock Species Affected:

  • Cattle
  • Sheep
  • Goats
  • Horses

Pasture, Stored Feed, Both:

  • Both (nitrate)
  • Pasture (hydrogen cyanide; typically dissipates when ensiled and in aging dried tissue)

Clinical Signs:

  • Difficulty breathing
  • Staggering
  • Falling
  • Convulsions
  • Coma
  • Depression
  • Blood of poisoned animals turns bright, cherry red from hydrogen cyanide
  • Blood of poisoned animals turns chocolate brown from nitrate poisoning

Amount Needed to be Consumed for Clinical Signs / Death:

  • Hydrogen cyanide
    • Forages that are >200 ppm hydrogen cyanide on an “as fed” basis are considered potentially dangerous
    • Forages >500 ppm hydrogen cyanide on a dry matter basis are considered suspect
    • Non-ruminant species (e.g. horses) typically less susceptible, as rumen microbes are more efficient at breaking down leaves and precipitating the release of hydrogen cyanide
  • Nitrate toxicity
    • Toxicity typically observed when forages have >1% nitrate or when 5000 ppm nitrate measured in dry matter
    • Nitrate toxicity is more common that hydrogen cyanide toxicity

Identifying Characteristics:

  • Grows up to 6 ft tall
  • Triangular panicle seedhead
  • White mid-vein
  • Jagged membranous ligule
  • Strong rhizome system

Plant Longevity:

  • Perennial warm-season-grass

Where Commonly Found:

  • Pastures
  • Fence rows
  • Ditch banks
  • Roadsides

Time of Most Concern:

  • Hydrogen cyanide toxicity
    • When the plant or tillers of a plant are less than 24 inches tall
    • After a hard frost in fall
  • Nitrate toxicity
    • During drought
    • High nitrogen application
    • Uptake of nitrate into plant after a rain that follows drought

Compound that Causes Concern:

  • Hydrogen cyanide, also commonly called prussic acid
  • Nitrate

Part of Plant Most Toxic:

  • Hydrogen cyanide
    • Young tillers
    • Immature leaf tissue
  • Nitrate toxicity
    • Lower stem

Livestock Species Affected:

  • Cattle
  • Sheep
  • Goats
  • Horses

Pasture, Stored Feed, Both:

  • Both (nitrate)
  • Pasture (hydrogen cyanide; typically dissipates when ensiled and in aging dried tissue)

Clinical Signs:

  • Difficulty breathing
  • Staggering
  • Falling
  • Convulsions
  • Coma
  • Depression
  • Blood of poisoned animals turns bright, cherry red from hydrogen cyanide
  • Blood of poisoned animals turns chocolate brown from nitrate poisoning

Amount Needed to be Consumed for Clinical Signs / Death:

  • Hydrogen cyanide
    • Forages that are >200 ppm hydrogen cyanide on an “as fed” basis are considered potentially dangerous
    • Forages >500 ppm hydrogen cyanide on a dry matter basis are considered suspect
    • Non-ruminant species (e.g. horses) typically less susceptible, as rumen microbes are more efficient at breaking down leaves and precipitating the release of hydrogen cyanide
  • Nitrate toxicity
    • Toxicity typically observed when forages have >1% nitrate or when 5000 ppm nitrate measured in dry matter
    • Nitrate toxicity is more common that hydrogen cyanide toxicity

https://extension.missouri.edu/publications/g4872

https://extension.okstate.edu/fact-sheets/johnsongrass-in-pastures-weed-or-forage.html

Beasely et al. Notes for Toxicology VB 320: A systems approach to veterinary toxicology. University of Illinois. 1994

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