By Linda Jones.
I drove up Interstate 5 at the end of March to central California and everything was so alive with color and greenery. All along the highway the hills were bright yellow with….Whaaat? Those are not California wildflowers covering the hills. It is that invasive black mustard, Brassica nigra or its relatives! The other non-native flower abundant in our hills and roadsides now is the garland daisy (Glebionis coronaria), an escapee from cultivation. Both are pretty this time of year, but at a cost to native plants.
Why are the hills of California covered in black mustard? Some blame it on the friars marking the trails to the missions with the yellow mustard. Seems like that would only have worked if people were going to the missions this time of year. However, the attribution remains.
Black mustard is native to southern Europe and Asia and it has been cultivated for making mustard and various cures, including easing arthritis pain (Maybe worth a try?). Regardless of how it came to be, it spread to acres and acres of hillsides and roadsides. The California Invasive Plant Council (Cal-IPC) lists black mustard as a moderately invasive non-native plant.
Allen and Roberts (in Wildflowers of Orange County and the Santa Ana Mountains) attribute the success of the mustard family to their rapid colonizing of disturbed areas where mycorrhizal fungi (critical to our native plants) are absent. Mustard then takes up soil nutrients and water, depriving the native plants of the habitat. The mustards also will crowd and shade out other plants.
Cal-IPC states that the black mustard produces allelopathic chemicals that inhibit native plant germination. In addition, black mustard can increase the frequency of wildfires in coastal sage scrub and chaparral communities. Such a bad actor.
If there is a bright spot, it may be that the checkered white butterfly (Pontia protodice) larvae feed on mustards, ingesting the plant toxins, which gives the adults protection from predation. However, they eat many other plants in the mustard family as well.
We had lovely rain this year and the result was a “superbloom”, including blooming black mustard, in many areas. However, sadly, in many areas, it will not matter how much rain we get in the winter. The beautiful native wildflowers still may slowly be lost to more competitive, non-native, invasive plants. The billboard at Camp Pendleton, below, was certainly a good reminder that we need to do more to protect our precious native wildlife areas or lose them to plants like black mustard.