Sahara mustard is a highly invasive weed that can spread and degrade native wildlife habitat at a fast pace. The recent discovery of small populations of Sahara mustard in multiple locations within the Irvine Ranch Natural Landmarks is causing concern, and now land managers are focusing efforts on eradicating Sahara mustard before it becomes entrenched.
Land managers in other parts of Southern California have already seen Sahara mustard (Brassica tournefortii) monopolize large areas of land. Fields once home to wildflower blooms have been replaced by this unwanted weed, driving out wildlife that depends on native plants there for food or shelter.
Sahara mustard starts growing earlier than most native plants, and the leaves at its base spread out in a wide “rosette” pattern, shielding neighboring plants from the sun. In a study by the University of California, Riverside, Center for Invasive Species Research, Sahara mustard was found to cause native plants to focus their resources on growing taller to escape the rosette shade, instead of producing seed. This caused a 90% reduction in native plant germination within the study area.
Another adaptation that allows the Sahara mustard plant to out-compete native plants is that its seeds are extremely hardy, germinate quickly, and can thrive in both wet and dry conditions. Each adult plant can produce up to 10,000 seeds, which can remain in the soil for several years. Not only does this help the plant spread rapidly, it also means that land managers are against the clock each year to remove the plants before they go to seed.
Sahara mustard is similar in many ways to the more widespread Black mustard and the fairly common Shortpod mustard (Hirschfeldia incana). The plants have similar leaves and stems, but there are a few ways to tell the plants apart. Black mustard stems grow up to six feet tall, while Sahara (and Shortpod) mustard only grows about three feet tall. Also, Sahara mustard plants have leaves that spread along the ground from the base of the plant, and the stems have smaller, less noticeable flowers than the showy yellow Black mustard blooms and the later-flowering Shortpod mustard.
Since Sahara mustard is not yet established in our local wildlands, there is an opportunity to stop the spread before it impacts native habitat within the Irvine Ranch Natural Landmarks. The Irvine Ranch Conservancy is tracking occurrences of Sahara mustard, and asks that visitors report any sightings of possible Sahara mustard along trails. If you think you see a Sahara mustard plant, please send an email to firstname.lastname@example.org with the location of the sighting, with a photo of the plant if you have one. Please do not attempt to remove the plant.
If you would like to help remove invasive weeds and restore native habitat in the Irvine Ranch Natural Landmarks, several volunteer opportunities are available. Volunteers work with science staff and trained stewardship activity leaders during these habitat restoration events. To find upcoming events, visit www.LetsGoOutside.org/Activities and select the Stewardship category in the menu.