Sorghum bicolor (L ) Moench ssp. bicolor—Cultivated sorghum
Sorghum bicolor (L ) Moench ssp. drummondii (Steud ) de Wet—Shattercane
Sorghum halepense (L ) Pers.—Johnsongrass
FAMILY: Gramineae (Poaceae)—the Grass Family (see Lolium)
PHENOLOGY: Depending on the taxon, environmental conditions and other factors plants flower from July to September.
DISTRIBUTION: Annual sorghum is cultivated widely in the United States. The domesticated types include broomcorn, sudan grass, grain sorghum, forage sorghum, and saccharin sorghum. Johnsongrass, a perennial introduced into the U S some time in the early 1 9th century, has spread as a weed of waste places, railroad yards, highway margins, and cultivated fields. In Pennsylvania it is more commonly encountered in the southeastern quarter of the state. Shattercane is an annual plant that results from crosses between cultivated sorghum and johnsongrass or as a spontaneous appearance of "wild'' (ancestral) genes in cultivated sorghum through genetic recombination. Shattercane is more commonly encountered in crop fields.
PLANT CHARACTERISTICS: Sorghum is a highly variable, diverse group of taxa too complicated to detail here. The spikelets are in pairs, numerous, and compressed, forming a large branching panicle, one spikelet of the pair sessile and perfect, the other pedicelled; glumes: about equal, hard; lemmas: thin, often awned. Sorghum halepense is perennial with narrow (4 cm) leaf blades. Members of the genus can attain heights of 10 feet or more.
POISONOUS PARTS: Green, aerial portions, especially leaves and stems, (canes) are toxic.
SYMPTOMS: Cyanide poisoning to livestock may result from consumption of plants. Mucuous membranes of eyes and mouth may appear congested. Ingesta examined immediately has a characteristic benzaldehyde odor, resulting from the production of benzaldehyde from the breakdown of the aglycone of certain cyanogenic glycosides. Respiration may be stimulated, rapidly altering to dyspnea, excitation, gasping. staggering, paralysis, prostration, convulsions, coma, and death.
Nitrogen poisoning can result from toxic levels of nitrates found in the plants. In ruminant digestion, nitrates are converted to nitrites, which are about ten times more toxic. They are the more immediate cause of poisoning. Symptoms of nitrite toxicosis include cyanosis, severe dyspnea, trembling, and weakness with a chocolate brown discoloration of the blood.
Postmortem: gross and histological lesions: bright red blood with congestion of internal organs; serious surface hemorrhage; respiratory passage edema may be present. Horses have been reported to develop chronic cystitis and ataxia and urinary bladder fibrosis in prolonged cases; epithelium ulcerations and abcesses may occur in the wall.
POISONOUS PRINCIPLES: Dhurrin, a cyanogenic glycoside, is present in some members of the genus Sorghum. Hydrolysis of this compound yields hydrocyanic acid. Forage sorghum also may accumulate levels of nitrates that can cause poisoning. Sheep developed hypersensitivity to light (photosensitization) due to a putatively photodynamic pigment in some species of Sorghum. For a complete characterization of photosensitization see Hypericum and Heracleum.
CONFUSED TAXA: As seedlings, virtually all species of Sorghum resemble one another and frequently are confused with young corn plants. Annual sorghum is either a cultivated plant or the weed shattercane.
SPECIES OF ANIMALS AFFECTED: Cattle mortality was extensive in some regions of the United States in years prior to the development of sorghum strains low in glycosides. Other livestock could be affected by the known sorghum toxins.
TREATMENT: (11a)(b), (25)
OF INTEREST: Some environmental factors that increase cyanogenic potential include high nitrogen, low phosphorus in soils, drought, and age of plants (young growth having highest potential). Many years of selective breeding have resulted in hybrids having low genetic potential for the development of hydrogen cyanide. Since S. halepense is a wild weed, it is to be considered with more suspicion than cultivated varieties, Sorghum halepense is a Pennsylvania Legislated Noxious Weed (Act 1982-74). Seeds of it (and those from any crosses) are Restricted Noxious Weed Seeds and must be listed on the tag or label of agricultural seeds for sale in the Commonwealth.