A rocky hillside near Cottonwood Springs Road is covered with vibrant green plants, thriving after a particularly wet winter. But it’s not all good news, as much of the area has been invaded by a pervasive noxious weed that threatens to choke out native species.
Sahara mustard, or Brassica tournefortii, is a short-lived winter annual native to Eurasia and Africa. It goes by many names, including Asian mustard, pale cabbage and African mustard.
It was documented in California in the 1920s and “has since invaded vast areas of the Sonoran and Mojave deserts,” Red Cliffs National Conservation Area wildlife biologist John Kellam told St. George News via email.
Utah designated the species as a noxious weed, which describes a nonnative plant that can disrupt or alter the function, composition or diversity of an ecosystem.
“Sahara mustard is well-adapted to desert landscapes, and with its high seed production capacity and ability to rapidly propagate under low soil moisture conditions, this weed is expected to thrive across a wide range of habitats,” Kellam said.
First detected in Washington County in as early as the 1970s, land stewards began noticing the plants in lower numbers more frequently in 2018 and 2019, Kellam said. Due to increased precipitation, the species increased from about 100 plants to over 18,000 on less than 10 acres.
Sahara mustard can produce more than 16,000 tiny, sticky seeds that may remain viable for over three years. They spread via wind or by attaching to animal fur, shoes, clothing and vehicle tires, among others, and eventually drop in a different location, “thereby pioneering a new infestation site,” Kellam said.
“Narrow seed capsules open when mature, releasing small seeds that are sticky when wet and impervious to water,” he said.
Sahara mustard grows rapidly in moist fall and winter soil, and Kellam said this early advantage allows them to outcompete native species. The plant can grow in “dense monotypic stands … creating this continuous mass of plants,” which can result in less diversity among native flora and fauna.
The plants can grow to 2-3 feet tall and have basal rosettes — groupings of leaves at the lower end of its stem — that are up to 3 feet wide, Kellam said over the phone. With finite water and nutrients in the soil, fewer resources are available when native species begin to sprout in infested areas.
The species typically flowers and grows seeds in early spring. Its small, four-petaled blossoms cluster in pale yellow at the end of its branches and its leaves are typically bumpy. Mature plants become tumbleweeds, allowing their continued spread, Kellam said.
Sahara mustard plants in Southern Utah have nearly completed their life cycles, said Brad Winder, Washington County’s Noxious Weed Control Department supervisor. They are expected to begin growing again in October or November.
These plants and other “highly invasive nonnative species,” such as cheatgrass or red brome, are “fine fuels.” Because they dry quickly, they can increase wildfire frequency and intensity, Kellam said.
“Without management intervention to control Sahara mustard and brome grasses, the Red Cliffs and Beaver Dam Wash National Conservation Areas will likely experience continued increases in wildfires that negatively impact desert tortoise population resiliency and recovery efforts,” he wrote.
While the Sahard mustard can be confused with other native and nonnative species, like London Rockets, Winder said they are “quite different.”
“It’s a little more aggressive,” he said. “It can take over pastures and range land if we let it.”
Land stewards use various strategies to manage Sahara mustard populations, but Kellam said that “early detection and proactive management is the best approach” as established stands are “difficult to control.”
Weed treatments and manual removal, such as hand-pulling, hoeing or grubbing are effective control measures, particularly before the plants flower and set seeds.
“Physical removal methods used consistently and repeatedly are effective at controlling Sahara mustard,” Kellam said. “In general, (the) effectiveness of physical methods is improved when combined with herbicide control.”
In December 2022, conservation area staff completed an Integrated Weed Management Plan and Programmatic Environmental Assessment to control and eradicate nonnative noxious or invasive plants within the Red Cliffs and Beaver Dam Wash National Conservation Areas’ critical habitats, Kellam said.
This spring, over 18,000 Sahara mustard plants inhabiting critical habitat were pulled and bagged by a nine-person Utah Conservation Corp crew during a project coordinated by conservation area staff. Kellam said they cleared less than 10 acres of the 50-acre infestation/treatment study plot.
Two scientists from the U.S. Department of Agriculture were present, collecting data on the infestation’s density and native plant composition, allowing them to evaluate pre- and post-treatment information when the area is treated with BLM-approved herbicides later this year, Kellam said.
Additionally, BLM staff from the St. George Field office treated various trailheads and 15 miles of road edges with herbicide.
Southern Utahns interested in supporting efforts to remove invasive species can volunteer for weed-pulling projects coordinated by the BLM, noxious weed control department or other community partners.
Winder said residents can reduce the spread of hazardous nonnative species by researching plants they wish to purchase using Utah’s Noxious Weed List or by Googling the species’ names to ensure they’re not considered invasive before planting.
Sahara mustard found on private property can be pulled or treated with herbicide. Winder said those discovered on public land can also be pulled if they are positively identified.
“If you pull it, you’re potentially saving the local area from 16,000 seeds,” Kellam said. “And you pull another plant — you can see how exponentially the benefit that comes from someone taking the minimal effort to reduce plants in their backyard, or in parks or along road edges.”
“It’s very important to properly ID a plant, especially if you’re in a natural area or adjacent to it,” Kellam said. “You just don’t want to be pulling any native mustards — they’re having a rough enough time competing with these exotic plants.”
While Sahara mustards can be described as “beefy,” native species typically occupy less space, said Dawna Ferris-Rowley, a manager for the Beaver Dam Wash and Red Cliffs National Conservation Areas, speaking on how to differentiate local plants from the noxious weed.
“Thank you, Dawna, for providing the title for the article: ‘Kill all beefy mustards,’” Kellam joked.
If a person is unsure of a potentially noxious plant’s species, they should report the sighting to Washington County’s Noxious Weed Department at 111 East Tabernacle Street or by calling Winder at 435-634-5702, sending him an email or uploading information to the EDDMaps app.
Source : St George News