The toxic substance in arrowgrass is hydrocyanic acid which becomes more concentrated when plants are growing under stress. Hydrocyanic acid poisoning results in abnormal breathing, trembling, convulsions, and death. Cocklebur is a broadleaved annual weed 2 to 4 feet tall with rough textured leaves and stems. Burs, 0.5 to 0.75 inches long, develop in clusters near the base of the leaves. The young seedlings are most poisonous and most often eaten by hogs.
Older plants are less palatable and less poisonous.
Cocklebur poisoning causes weakness, rapid breathing, convulsions, and death. Cocklebur occurs mainly around water and on flood plains, and is most common is the southeastern part of North Dakota. Sneezeweed is a leafy perennial plant which grows 1 to 2 feet high with yellow sunflower-like heads, 0.75 inch wide, that appear in August. Sneezeweed grows in low moist areas and is not common in North Dakota. Sneezeweed poisoning is most common in sheep and causes vomiting, coughing, and bloating.