African Rue

Peganum harmala L.

Zygophyllaceae (Caltrop family)

Description

African rue is an introduced, deep-rooted, perennial plant in the Caltrop family. The plant is a succulent, bright green herb growing from a woody base. It is bushy, many branched and about 1 foot tall when fully grown. The leaves of African rue are hairless, divided into narrow segments and located alternately along the stems. The flowers consist of five white petals and are present from April to September. Segmented seed pods develop from May to October. The forage value of African rue is poor for livestock and wildlife, and the plant is extremely unpalatable. It is also poisonous to livestock and is consumed only when animals are starving.

Habitat

African rue is found in a variety of soil types but thrives in disturbed areas, roadsides and abandoned cropland.

Toxic Agent

African rue, which contains at least four poisonous alkaloids, is toxic to cattle, sheep and probably horses. The seeds and fruit of the plant are the most toxic; a lethal dose is 0.15 percent of the animal's body weight. Young leaves are somewhat less toxic than seeds, with a lethal dose of about 1.0 percent of the animal's weight, while mature leaves are less toxic. Dry leaves are apparently nontoxic.

Signs of Livestock Ingestion

Signs of chronic poisoning include: loss of appetite, listlessness, weakness of the hind legs, knuckling of the fetlock joints Acute conditions produce these signs: stiffness, trembling, incoordination, frequent urination The body temperature of poisoned animals is usually subnormal. They salivate excessively, wetting the lower jaw and muzzle. Postmortem examination may reveal hemorrhages on the heart or liver. Acute poisoning usually is caused by eating seeds.

Management Strategies

African rue is extremely unpalatable. Animals eat it only if they are starved or suffering from severe mineral deficiencies. If poisoning occurs, it is usually in spring and summer. When possible, avoid pastures infested with African rue during these times. Remove livestock known to be grazing young leaves or seeds of African rue from the area. If given good-quality feed and water, chronic poisoning cases generally recover. Chemical control treatments for African rue should target problem areas such as roadsides, livestock pens and traps, and areas around oil fields.