Herbicide-Treated Plot

Untreated Plot

Sahara mustard is an exotic winter annual native to North Africa and is the dominant winter plant across wide stretches of Southern California. Research on control methods in the desert environment is lacking.

Methods: Two levels (high and low application rates) of four herbicides were tested, Chlorsulfuron, Glyphosate, Triclopyr and Pelargonic acid (Scythe), thus resulting in 8 chemical treatments. These chemical treatments were compared to a hand-pulling treatment and an untreated control. The study was replicated in Borrego Springs and Palm Desert, California.

Results were variable between chemicals, Triclopyr had the greatest control of Sahara mustard, with reductions in mustard over 99%, and Chlorsulfuron exhibited reductions over 95%. However, these two chemicals do not control invasive grasses (Mediterreanean grass, Schismus species), which dominate after broadleaved plants are removed. These two chemicals also removed most of the native wildflowers in the research plots and should be used with caution if management goals are to preserve established wildflowers.

The high Pelargonic acid and both Glyphosate treatments exhibited acceptable control of Sahara mustard with greater than 85% reduction. The low Pelargonic acid treatment only had a 40% reduction. Glyphosate and Pelargonic acid also had the greatest post-treatment survival of native plants at 35-85% survival compared to control plots. However control plots had a low cover of native wildflowers (avg. 7% cover) because of competition with Sahara mustard.

When hand-weeding treatments remove Sahara mustard, native plants can thrive. Almost 30% of the hand-weeded plots were covered with other annuals. This is twice as much area compared to any other treatment, including untreated plots.

Results in the Coachella Valley were similar, however Pelargonic acid and the low Glyphosate treatment were not effective at the Palm Desert site.

The table below contains the results for our Borrego Springs research. Numbers represent averages for each column. The best treatment will have the greatest number of black or yellow numbers with the least amount of red numbers. For example, with the Brush-B-Gon High treatment % Native cover is very low and I assume managers would like to preserve their native plant cover, thus this is a red number.

Because herbicide concentrations can vary between products please contact ME or Carl Bell for application rates.

Certain herbicides can be effective at controlling Sahara mustard (Brassica tournefortii), yet the successful treatment will depend on site-specific management goals, such as the preservation of established wildflowers, and acceptable mortality rate of Sahara mustard.

Research Updates