Noxious Weeds Profile - Johnson Grass

Table of Contents

  1. Names
  2. Photos
  3. Current Status
  4. Poisonous/Cautions
  5. Distribution
  6. Growth Habit
  7. Method of Propagation
  8. Control
  9. Other Comments
  10. Related Links


  • English - Johnson grass
  • French - sorgho d'Alep
  • Latin - Sorghum halepense (L.) Pers.
Johnson grass (A - infestation in field; B - large whitish rhizomes produced after plants head out).
Johnson grass (A - infestation in field; B - large whitish rhizomes produced after plants head out).

Current Status

  • Ontario Weeds Act - noxious
  • Other provinces - none
  • Canadian Federal Seeds Act - Class 2
  • U.S. Federal Noxious Weed - no
  • U.S. Noxious State Reg - 26 states (including Mich, Ohio, Indiana, Illinois, Minnesota, Penn)


  • Pub 505 - no
  • NE Weeds - no
  • Canadian Poison Plant - This plant can produce toxic quantities of HCN if it is damaged through frost, mastication, or water stress. Johnson grass can also accumulate toxic amounts of nitrate under certain circumstances. Cattle and a horse were poisoned after ingesting Johnson grass. Plants are spread from rhizomes but susceptibility to severe frost has limited the plants to a few counties in southwestern Ontario. The grass is found in fields and field edges. Toxicity is not likely, but ingesting large quantities of Johnson grass can cause problems (Gray et al. 1968, Clay et al. 1976, Warwick and Black 1983).
  • Cornell Poison Plant - referred to Canadian site
  • Indiana Toxic Plants: TOXICITY RATING: Moderate to high. ANIMALS AFFECTED: All types, especially ruminants. DANGEROUS PARTS OF PLANTS: Leaves and stems, especially young plants. CLASS OF SIGNS: Breathing problems, staggering, severe anxiety, convulsions, coma, death (may be very sudden).


  • Not commonly found in Ontario. Does not usually overwinter in Ontario but occasionally found overwintering in protected areas such as near woodlots or river valleys.

Growth Habit

  • Perennial

Method of Propagation

  • Seeds, Roots/rhizome


  • Difficult to control and very competitive with row crops such as corn and soybeans.

Other Comments

  • Johnson grass has been reported to be a source of aster yellows virus.

Related Links

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