The Sahara Mustard & Volutaria Weed Eradication Task Force

Guidelines for the treatment of Saharan mustard (Brassica tournefortii) within Anza-Borrego Desert State Park®

Background: Saharan mustard (Brassica tournefortii) is a member of the mustard family (Brassicaceae) and is native to the arid regions and deserts of North Africa, the Middle East, and Southern Europe surrounding the Mediterranean Sea. Botanists believe that it was introduced several times into Southern California and Arizona in the early part of the twentieth century, and locally seeds likely hitched a ride in the seeds and plant stock of date palms that were planted in the Coachella Valley in the early 1920s.

It is an extremely invasive annual species that has become an increasing threat to annual desert wildflowers and other native species in several western states. Unfortunately there is not now an effective way to treat large areas of infestation, but locally we can reduce the threat in selected areas within the park. Anecdotal reports indicate that Saharan mustard may be substantially decreased where it is not common if there is follow-up treatment in subsequent years.

Description: Saharan mustard is an annual plant that has a basal rosette of turnip-like lobed leaves that are covered with bristly hairs and produces mostly leafless branching flowering stalks that extends above the basal leaves. Larger plants may also have lateral flowering shoots arising from the base of the plant. The flowers are pale yellow and have four petals later producing long, narrow seed pods. Plants may vary in size from a few inches tall in drier areas to very robust plants that are often 2 – 3 feet across in wetter areas, especially in sand, washes, and along roadsides. The mustard uses up water and nutrients and crowds out the native plants.

Saharan mustard seeds commonly germinate after the early winter rains, but occasionally they will germinate after late summer and fall storms, generally after August. There may be a series of germination events after each storm, creating a mosaic of plants of different sizes and stages of development. It may be necessary to revisit the site after each storm. Also, plants may appear in areas where you may have not seen them before.

It is important to know that there are similar looking native plants that often co-occur with Saharan Mustard and an effort should be made to learn the differences with someone trained in plant identification during a scheduled training session.

1) Tansy mustard (Descurainia pinnata) is an annual plant that has very finely divided gray-green leaves and small yellow four-petaled flowers producing short club-shaped seed pods.

2) California Mustard (Guillenia lasiophylla) has tiny white to cream-colored four-petaled flowers. The leaves (although variable) are usually scalloped or comb-like and are smooth to the touch. This delicate plant is somewhat lax and often grows at the base of small shrubs.

3) False mustard (Camissonia californica) a native plant in the evening-primrose plant family that may be mistaken for Saharan Mustard because it has relatively larger yellow four-petaled flowers. It has scalloped to toothed leaves that are often red-dotted and are smooth to the touch. The long seed pods are reflexed down along the axis of the stem.

You may find photos of the plants listed above online at Calphotos – plants  http://calphotos.berkeley.edu/flora . On the homepage browse using the first letter of the scientific name, the genus name, for example, “C” for Camissonia, then in the next window, scroll down until you find the two word scientific name Camissonia californica on the list and click on that. Incidentally, the common name False Mustard does not occur on the common name list. There may be several common names for a plant, therefore it’s better to browse using the scientific name.

Treatment: Early treatment is essential. The mustard seeds may germinate before many of the native wildflowers, but not always. You will soon develop a ‘search image’ for the plant in the various stages of development and be able to distinguish it from the wildflower seedlings.

At the Henderson Canyon Road site, we have found that carefully weeding with a hand-held weeding tool is more effective than using a hoe where the mustard is growing close to the native plants. You may use a stirrup hoe (a long-handled tool with an oval cutting edge). It is better than a garden hoe because it doesn’t drag as much soil with it but cuts the plant at ground level.

Small pulled plants can be left in the field as long as they don’t cover native plants. In the past, we have started treatment late in the season when the plants were in flower and/or fruit, but that required a lot of extra work to pull, bag and dispose of them. Later in the season before the larger plants produce mature seed pods, they will need to be bagged and removed from the site.

Field equipment: sturdy boots, gloves, plenty of drinking water, snacks, sunscreen, wide-brim hat, and a hoe, and hand shears to cut off the taproot and the flowering stalks of larger plants later in the season.

Authorized Limited-Term placard for 2010-11: Park volunteers must attend one of the scheduled training sessions. You will be required to fill out a volunteer service agreement and will receive a placard (permit) to work within the park. Please display this placard in the window of your vehicle when you enter Borrego Palm Canyon Campground, or are working elsewhere within the park. Anza-Borrego Desert State Park volunteers who have had previous training may pick up a placard from the volunteer coordinator at the Visitor Center or contact Larry Hendrickson (phone number and email address below).

The following suggestions will help us reduce any negative impacts to native plant species and ensure that the park visitor experience is not affected by this activity:

  • Select an area and survey it first. Smaller plants often occur in the drier gravelly soil and are almost invisible. These plants will often mature faster (bolt) than plants in wetter areas, that is, they may have already produced flowers and seed pods. These smaller mature plants should be bagged for removed. Also, smaller less developed plants are often hidden in the shade at the base of shrubs and cacti. You may be able to use your weeding tool to remove these.
  • Be careful not to disturb native vegetation. If working with others, spread out so that you minimize trampling of native annual plants.
  • For aesthetic as well as safety reasons, do not dispose of plants on or at the edge of trails.
  • Be vigilant for rattlesnakes at any time of year.
  • Do not place pulled plants on top of other plants or toss them onto shrubs. You may place plants in a bare area nearby or on top of boulders. You make stack them if space is limited, but piled plants may not dry sufficiently, and surprisingly, the larger plants have enough energy to continue to grow even after they have been pulled out of the ground!
  • There are many rodent burrows at the Henderson Canyon site, usually several holes surround a mound of sand. Do not walk on them because you may sink into the burrow. Use a hoe to remove the mustard around them.
  • Limited-Term volunteers must keep a record of hours and where they worked and convey that information to Larry Hendrickson. ABDSP volunteers should record their hours at the visitor center and report hours to Larry Hendrickson.
  • Do take the opportunity to educate interested park visitors about the program. If asked, explain that they will not be able to pull mustard in the park without attending a training session and have written permission to do so.

Thank you very much for your help!

Larry Hendrickson, Senior Park Aide, California State Parks, Colorado Desert District, 200 Palm Canyon Drive, Borrego Springs, CA 92004

 

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