Pepperweed could become new nemesis to area rivers

| Saturday, September 30, 2000 10:00 PM PDT ∞

DAVE DOWNEY
Staff Writer

TEMECULA ---- When workers begin spraying herbicide this month to try to eradicate the bamboolike arundo plant from the Santa Margarita River, they will be looking out for another exotic plant that could pose an even worse threat to the fragile river environment down the road.

For the moment, weed control efforts along the watershed through southwest Riverside and northwest San Diego counties are focused on arundo, or giant reed, and tamarisk. A coalition of government agencies that recently organized as a nonprofit group is preparing to send workers equipped with backpack-mounted sprayers into the field in a couple weeks to knock those plants down. They will be spraying rodeo, which is approved by state and federal agencies for use around water and milder than other herbicides.

Judy Mitchell, district coordinator for the Fallbrook-based Santa Margarita and San Luis Rey Watersheds Weed Management Area, said sprayers will start on Murrieta Creek ---- a Santa Margarita tributary ---- in Temecula and work their way downstream.

While the team is out ridding the river of arundo and tamarisk to give willows and native vegetation more room to grow, members will comb the river ecosystem for the pepperweed plant.

Commonly called tall whitetop by farmers because of its dense clusters of white flowers, the nonnative plant is growing in the stream in places such as beneath the Main Street bridge in Old Town Temecula.

"We're finding (pepperweed) all along the Santa Margarita," said Jason Giessow, an Oceanside plant biologist who has contracted with the weed management agency to spearhead the eradication campaign and develop a plan for the pepperweed plant.

The total area occupied by pepperweed is about 100 acres, Giessow said. That's not a whole lot for a watershed that has numerous tributaries in Riverside and San Diego counties, including Murrieta Creek in Temecula, he said. But the plant can spread so explosively that officials want to prevent it from becoming a major infestation.

Said his wife and business partner, Jesse: "It can be tame for a while and then just really take off."

The Giessows are going to survey the watershed this fall for pepperweed and map its distribution, then develop a strategy for fighting that has a reputation for being very competitive, crowding native plants out in only a few years.

Another agency ---- the San Diego Weed Management Area ---- is targeting three infestations of pepperweed in the San Pasqual Valley, along Santa Maria Creek and in Moosa Canyon, according to the group's Web site. Both weed-fighting agencies formed earlier this year.

Bill Winans, environmental management specialist for the San Diego County Department of Agriculture/Weights and Measures, said plans are being laid to treat those areas next spring.

"The infestation in the San Pasqual Valley is the largest in our county," Winans said. "It may be 500 acres or more."

While arundo has caused much more harm to Southern California riverbeds to date ---- the rapidly growing plant with bamboolike stalks and cornlike leaves has infested 10,000 acres along the Santa Ana River in northern Riverside County ---- the pepperweed plant is perhaps an even bigger threat, Jason Giessow said.

Pepperweed, like arundo, colonizes new territory by sending out long, lateral roots that sprout new shoots. But, unlike arundo, the pepperweed plant sprays numerous seeds as well. Even when workers successfully wipe out particular colonies by spraying, new ones tend to crop up all over from the seeds, which easily wash downstream when it rains, Giessow said.

Pepperweed can produce more than 6 billion seeds per acre, according to a Web site posted by the University of Nevada.

Native to southern Europe and western Asia, pepperweed belongs to the mustard family. It was accidentally brought into this country in bags of sugar beet seed delivered to Yolo County about 100 years ago, according to the California Exotic Pest Plant Council.

The plant is capable of elbowing out a whole range of native plants and transforming riverbeds into dense fields of white-flowering plants one to three feet high. That could potentially devastate areas that are crucial habitat for endangered birds such as the California coastal gnatcatcher and the least Bell's vireo.

Pepperweed, too, is so hardy it can grow in a wide range of climates. It is found not only in the coastal salt marshes of California, including San Diego County, but also at 8,000-foot-high Donner Summit on Interstate 80 in Northern California.

The plant has taken over thousands of acres throughout each Western state, except Arizona. Because of its range and rapid rate of growth, officials responsible for managing rivers and agricultural areas have given up hope of eradication and are concentrating on controlling its distribution.

That's why officials in Riverside and San Diego counties want to attack the plant quickly and decisively before it grows out of control locally, Giessow said. But, he said, because there is little money available at the moment, the Fallbrook-based nonprofit must secure grants before launching a campaign along the Santa Margarita River.

Contact Dave Downey at (909) 676-4315, Ext. 2621, or downey@nctimes.com.

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