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Arrowgrass is a perennial that has fleshy, dark-green, half-rounded, grasslike leaves that grow from the base of the plant. Although clumps of leaves are only 6 to 18 inches tall, slender flower stalks may reach a height of 5 feet. Small, green flowers appear close together along the upper part of the stalk early in the season. Later, the flowers develop into golden-brown fruits.
Where and When it Grows Species of arrowgrass are widely distributed in marshy areas and wet meadows throughout the United States. Arrowgrass grows on wet, alkaline soils and may be found growing over large areas or small patches near springs. Arrowgrass starts growing in early spring. It is often found growing in native meadows that are cut for hay. Arrowgrass cut for hay may be toxic.
Arrowgrass that is growing with adequate moisture does not cause poisoning. When growth is stressed or stunted from lack of moisture or frost, plants quickly become toxic. Regrowth foliage following harvest is also toxic. The toxin in arrowgrass is the same as that in chokecherry.
Signs and Lesions of Poisoning
Dyspnea; rapid breathing and gasping
Cyanosis (blue discoloring of the lining of the mouth)
Muscular twitching, staggering, and convulsions
Bloat may occur; rumen contents may smell like almonds
Death (animals consuming large amounts of the plant may die in 1 to 60 minutes and show only convulsions and death as signs of poisoning)
Blood and tissues a bright cherry red (hyperoxygenation)
Tracheal and pulmonary congestion
Cattle and sheep may be severely affected if they eat large amounts of arrowgrass leaves or stalks in a short time. The leaves contain substances that produce the poison hydrogen cyanide on ingestion.
How it Affects Livestock The amount of arrowgrass required to poison sheep or cattle depends on the amount of poison in the plants and the rate at which the plants are eaten. There is enough hydrogen cyanide, also known as hydrocyanic acid or prussic acid, found in 1/4 to 3 lb of stunted arrowgrass to kill a 600-lb animal. The toxic dose must be eaten at one time to cause death because the poison is not cumulative. Death results from respiratory failure.
How to Reduce Losses Keep animals off areas where the growth of arrowgrass has been retarded by drought or frost or regrowth following harvest. The action of hydrocyanic acid is so rapid that it is usually too late to treat an affected animals after the signs of poisoning are recognized. Some poisoned animals may be saved by immediate treatment with an intraperitoneal injection of a mixture of 20ml if a 10-percent solution of sodium thiosulfate and 10ml of a 10-percent solution of sodium nitrate. For animals in advanced stages of poisoning, give an intravenous injection of the sodium thiosulfate and sodium nitrite solution. Consult your local veterinarian regarding treatment.
Arrowgrass can be controlled by metsulfuron (0.5 oz product/acre) when applied during seed stalk elongation.