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War on Purple Plague
Cameras and eyeballs discovered the magenta spikes of one of California's prettiest pests in the Delta this year, confirming the spread of purple loosestrife (Lythrum salicaria) from the upper to the lower watershed. The surveys by airplane, boat and foot, and education efforts aimed at revealing the ugly side of this pretty aquatic plant, represent the first year of a three-year project aimed at extinguishing the European invader before it's too late.
Too late, that is, for the native flora and fauna at the edges of Bay-Delta waterways. In many states, this 'purple plague' is the top nuisance plant and makes up more than 50% of the biomass of emergent vegetation, closing the canopy and leaving a virtual biological desert underneath. Scientists say that other common wetland plants can't compete, that loosestrife can impede waterflow and storage, and that its leaves decay so much more rapidly than those of the resident vegetation that they only supply detritus important to the food web of juvenile salmon in the autumn, rather than throughout the winter and spring.
Luckily for California, the new survey indicates an invasion that is still very controllable. But it also revealed previously unreported infestations in the Delta's Middle and Old Rivers, and along the Calaveras and Tuolumne Rivers, according to Carri Benefield, who heads up the CALFED funded control project for the Calif. Dept. of Food and Agriculture. Upstream areas have had the purple plague much longer, with documentation in Shasta and Butte counties dating back to the 1950s.
Though killing pretty plants is a "tough sell," that's exactly what Benefield's program is trying to do. Armed with the survey data, the project will now work with local groups to develop action plans mobilizing three types of possible control methods: hand removal for infestations of less than 100 plants; spraying with herbicides for bigger jobs; and various combinations of the two, with the possible addition of some European beetles known to munch loosestrife to the ground.
"The fact that these plants are aquatic limits our control options right off the bat," says Benefield. "Access is a big problem, you can't dig from a boat as easily as from the ground. And using chemicals in waterways can be a water quality worry."
One thing plant removers have to be careful of is the loosestrife's copious production of seeds the size of ground pepper. Pulled plants have to be bagged and destroyed, and mature plants removed with care because disturbance often creates a new flush of seedlings. "You don't want to dig at the wrong time, otherwise all the seeds could float downstream," warns Benefield. "You have to commit yourself to a multi-year process." The long maintenance commitment may buy some time to mobilize the beetles, however, whose use in California is still in the testing phase.
In the meantime, Benefield has been spreading word of the plague - giving over 50 talks so far - to garden clubs, government staff, ecologists, and weed management groups. "I tell people that on the East Coast, there are places where purple loosestrife stretches as far as the eye can see. I tell them purple loosestrife could be the next yellow star thistle" (a familiar yellow prickler now displacing California grasslands).
The plague is still at an early enough stage that it can be stopped, says aquatic weed researcher Lars Anderson of the U.S. Department of Agriculture. "But we have to remember that once it gets into the Delta, with tides moving seeds in every direction every six hours, it could spread very rapidly." Contact: Carri Benefield (916)654-0768 or see www.cdfa.ca.gov/purpleloosestrife ARO
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