Species specifics: African rue

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Fast facts about African rue

Highly toxic to livestock and humans including cattle, horses and sheep.
African rue is also commonly referred to as wild rue or rue weed.
Nonnative to the United States, this perennial wood succulent plant is found throughout much of the Southwestern United States, including Arizona, California, Nevada, New Mexico, Texas and Utah, with additional populations becoming a problem as far north as Idaho, Montana, Oregon and Washington.
Aggressive, invasive and generally difficult to control without herbicide treatments.

What to look for

African rue (Peganum harmala), also commonly referred to as wild rue or rue weed, is a nonnative, noxious perennial weed that contains multiple compounds toxic to both livestock and humans and can inhibit the growth of neighboring native plants.

The plant features green, succulent-like foliage and typically grows 2 to 3 feet tall, with a woody base and an extensive root system. Leaves are smooth, alternate and deeply divided into narrow lobes. When crushed, they emit a strong, unpleasant odor.

While its aboveground spread generally does not exceed 4 feet in diameter, African rue develops an extensive root system that includes a taproot that reaching 25 feet or more, and lateral roots starting around 12 to 15 inches below the soil that can spread as far as 20 feet in radius from the parent plant. New plants can sprout from the parent plant off the lateral roots.

Single white, five-petaled flowers bloom from a stem or along the forks of leaves in late spring through summer that yields fruits that contain seed pods that can be green, orange or brown. Each African rue can produce more than 1,000 seeds annually. African rue spreads by both seed and root fragments. Seeds and root pieces may be transported by animals, vehicles, farm equipment or moving water such as flash floods common in the arid regions where this plant is found.

Plants will often become senescent (or dormant-like) after its first spring green-up and flowering and will die back to its base through the heat of the summer. By fall, once temperatures have slightly fallen and moisture levels rise again, African rue will go through a second vegetative cycle until a hard freeze. Mature plants die back to their roots overwinter and reemerge from roots in early spring, generally in March or April.

The weed is highly toxic to livestock including cattle, sheep and horses, as well as humans. Seeds, fruits and leaves all contain toxic alkaloids in varied degrees. Much of the plant also contains allelopathic chemicals that act as growth inhibitors to surrounding native plants. In general, animals avoid eating African rue thanks to its bad taste and smell, but care should be taken in pastures where this weed is present to ensure enough other favorable forages are available for animals to consume.

Where it is found

Noxious in Arizona and New Mexico, African rue is also found throughout California, Idaho, Montana, Nevada, Oregon, Texas, Utah and Washington. The weed is highly drought tolerant, often exhibiting, and thrives in a variety of soil types. Disturbed areas such as those recently cleared, tilled or heavily grazed are susceptible to new population booms of African r

How to treat it

African rue is a difficult weed to control or eradicate due to its ability to reemerge from root pieces or lateral root shoots. It is also not a plant that is controlled by burning. African rue will readily reemerge after a burn, often stronger than before.

Combined with its allelopathic chemicals that allow it to outcompete neighboring favorable forages and native grasses, African rue is a weed to manage with herbicide treatments as soon as a new plant is found in pastures or rangelands.

Treat African rue plants with Spike® 20P herbicide for both broadcast applications and individual plant treatments (IPT).

Broadcast: Apply at 7.5 to10 pounds per acre.
IPT: Use 0.50 ounce of pellets per 100 square feet. If using the Spike 20P 5-pound canister, one pull will deliver approximately 0.33 ounces.

Do not use Spike 20P in heavy clay soils. Poor control or erratic results are likely to occur when applied to soils containing more than 5% organic matter or more than 30% clay.

Spike® is a registered trademark of Nutrichem used under license. Always read and follow label directions.