A New Weed in Anza-Borrego

Threats and opportunities for eradication

Chris McDonald
Natural Resource Advisor
University of California Cooperative Extension
cjmcdonald@ucanr.edu
A young Volutaria plant

A new and highly invasive weed is spreading in Borrego Springs including in Anza-Borrego Desert State Park (ABDSP). Volutaria (Volutaria tubuliflora) was first discovered in Borrego Springs in 2010 in ABDSP. It has also been discovered in Chula Vista and Newport Beach. In the past six years Volutaria has been found in over 20 locations in Borrego Springs, making it the largest of the three known Volutaria infestations. It is unknown how Volutaria arrived in California; it is, however, making itself an unwanted guest and threatening desert and coastal communities.

Volutaria poses several threats to the Park. Volutaria can grow in thick stands potentially reducing native wildflowers. It grows taller than most wildflowers, shading out its native neighbors. And because Volutaria is taller and much less attractive than the native wildflowers it can obstruct the brilliantly colored wildflowers, leading to a reduced spring flower bloom.

Volutaria also does not appear to be very palatable to wildlife. While caterpillars and rabbits have frequented populations of wildflowers adjacent to Volutaria plants, most Volutaria plants show limited signs of grazing. It is possible that Volutaria contains chemicals that leave a bad taste in the mouths of herbivores. This means that as Volutaria increases in numbers and crowds out native plants there is less food available for native herbivores including rabbits, butterfly and moth caterpillars, and even pollen for our numerous bee species.

A patch of flowering Volutaria plants growing faster and taller than the native plants

In Borrego Springs, Volutaria can be abundant along roadsides. This means that visitors can inadvertently pick up seeds on their clothes, boots, pets, cars and bikes as they spend a day, weekend or month in Borrego Springs and then carry them a long distance back to their home. They can also accidentally spread the seed locally by visiting an infested site with mature seeds and then unknowingly carry the seed to a new stop later in their trip. Cleaning your equipment and clothes before and after a trip is one way to prevent the spread of Volutaria. Without containing the spread of Volutaria the chances of eradicating this weed are greatly reduced.

Volutaria is in the sunflower family and has relatively small unattractive flowers. It is closely related to knapweeds and star thistles. These two groups of plants are well known among botanists and land managers across the Western United States because they contain numerous and noxious weeds including yellow star thistle (Centaurea solstitialis) and spotted knapweed (Centaurea stroebe ssp. micranthos). This is the first introduction of Volutaria tubuliflora in North America and it threatens to be just as invasive as its close relatives.

Volutaria plants have a distinct shaped leaf (a quarter for scale)

In its native range in the Mediterranean and North Africa, Volutaria can occupy a variety of habitats from disturbed areas, grazed pasture, farms, rocky slopes, extremely dry deserts and coastal plant communities. All of these types of plant communities are found in Southern California. ABDSP contains several of these habitats and the potential for this weed to flourish locally and across the region is high. So far, most Volutaria populations are in the central portion of Borrego Springs and in locations that are easy to access. Other weeds in ABDSP are in very isolated and difficult to reach locations, which hinders their removal. Despite the ease of accessing Volutaria populations, it is spreading rapidly and without a significant effort to control this weed it could spread beyond our capacity to eradicate it from California, creating another threat to our deserts.

One of the ways you can help is to learn more about Volutaria: how to identify it, how to keep it from spreading, how to keep it out of your yard and volunteering to pull it. ABF will be working with Anza-Borrego Desert State Park to organize weekly volunteer weeding events every Thursday from January 26 and continuing through March 30.  You can get all the event details on the ABF website. You can also learn to identify Volutaria and how to keep it from spreading. Because this noxious weed is a recent invader and is, so far, found in only a few places in Southern California, there is a chance an organized effort can successfully eradicate this weed from North America and prevent it from spreading across the Park as well as the rest of the desert.