Beetles saving county's wetlands from purple alien invader

2004 Archived News

close up of purple loosestrife flowers

Purple loosestrife, that striking magenta wetland invader, was highly conspicuous in King County wetlands as recently as last year. But look again. Thanks to a voracious weed-eating beetle, along with the hard work and cooperation of state, federal and county agencies, purple loosestrife is slowly disappearing. On Thursday, the King County Noxious Weed Control Program and WSU Extension, in cooperation of King County Parks, will be releasing Galerucella beetles on purple loosestrife at King County's Marymoor Park in Redmond and at a larger infestation near the Auburn SuperMall as part of ongoing noxious weed control efforts. "The measure of success for this program is not seeing those plants where we've historically had infestations, and we're starting to get to that point," said Steven Burke, King County Noxious Weed Control Program manager. "What's great about these beetles is that, because they only eat purple loosestrife, introducing them has only a positive impact on our ecosystem."

Burke said about 300 beetles will be released at Marymoor and about 1,000 in Auburn. Beetles have previously been released at both locations and Thursday's release will supplement established populations.

Galerucella beetle on purple loosestrife leaf; feeding damage is evident

Why is purple loosestrife a problem?

Purple loosestrife is a perennial plant that can reproduce both vegetatively and by seed. Large plants can produce more than 2 million seeds the size of ground pepper. These seeds are stored in the soil seed bank, and when conditions are right, purple loosestrife expands unhampered through our wetlands. Purple loosestrife displaces native vegetation, which in turn displaces wildlife. The hydrology and ecology of a site is changed, greatly reducing habitat values, water quality benefits, and species diversity typified by a healthy wetland system.

Purple loosestrife was originally introduced from Europe in the ballast of ships in the 1800's. It came over without any natural predators, and was therefore able to establish and spread here with nothing to slow it down. Recent research indicates that many plants quickly adapt when they no longer have to fend off natural enemies. They are better able to out-compete our native plants, which have many natural controls to deal with – including their own natural enemies and other invasive plants.

How is purple loosestrife being controlled?

A humble beetle that only eats purple loosestrife is slowly but surely devouring it. The Galerucella beetle is native to the same range in Europe and Asia as purple loosestrife. Unlike purple loosestrife, the beetle was deliberately brought over in the 1900s as a biological control agent. King County Noxious Weed Control Program Staff have been releasing Galerucella beetles in King County since 1997. This year, in collaboration with WSU King County Extension, beetles were already released at four sites, including sites in Woodinville, Auburn and Seattle. In areas where the purple loosestrife is not dense enough to support beetles, program staff works with landowners to control it by hand. The end result has been a significant reduction in purple loosestrife.

What is biological control?

Biological control is the use of a living organism to suppress the population of a pest to an acceptable level. In this case, the pests we are attempting to suppress are noxious weeds, and the living organisms that we use are insects. Research is conducted by USDA Agricultural Research Service European Biological Control Laboratory to make sure the introduced organism will only eat the specific target weed, and will do enough damage to the weed to be an effective control.

Biological controls can control the target weed directly or indirectly, but they will not eradicate the plant populations from a site. Weeds are directly impacted when the biocontrols destroy plant parts that prevent growth, or prevent seed production. Biocontrols impact a weed indirectly when the stressed plants are no longer able to out-compete native or beneficial plants on a site.

It can take 4 to 5 years for any visible signs of weed control, making this an effective tool in a long-term control plan.

Want more information?

For more photos and information on purple loosestrife and other noxious weeds, contact the King County Noxious Weed Control Program at 206-296-0290 or visit their Web site.

For more information regarding biocontrol of purple loosestrife and other noxious weeds please contact Tara Zimmerman at WSU King County Extension at 206-205-3203 or tara.zimmerman@kingcounty.gov.