Most Unwanted -- Watch Out For The Weedy Outlaws Of The Plant World

LOOSESTRIFE, RAGWORT, hogweed, toadflax - the names sound like a witch's curse. Yet the blossoms of these plants are attractive, if not beguiling. See them along the road and it seems natural to invite them home to your garden.

Many people have, but beware: Their exotic beauty comes at a high cost.

These and other noxious weeds are our unwelcome neighbors. They ruin native plant and animal habitat, push us out of recreational areas, spoil food crops, clog waterways, poison or injure humans and livestock and lower land values. About one-quarter of Washington's gross agricultural product is lost to noxious weeds - those imported plants that are injurious or harmful to health and very tough to control.

Noxious weeds cost U.S. farmers and ranchers more than $5 billion a year to control, according to Secretary of the Interior Bruce Babbitt, who gave a tough war-on-weeds speech last April at a weed-management symposium in Denver. During that talk he said that noxious weeds wreak havoc on America's environment and economy "matched only by damage caused by floods, earthquakes, mudslides, hurricanes and wildfire."

Of course, not only farmers and ranchers are affected. All of us who use the outdoors or pay taxes have a stake in the fight. The congressional Office of Technology Assessment has predicted that biological invasions will become one of the most prominent ecological issues on earth.

The weed war is an old war, even in the Northwest. Back in 1881, Washington Territory adopted a law to control the spread of foreign thistles. Today, there are tough weed laws on the books across the Northwest - there are even "War on Weeds" billboards in the remote Montana countryside - yet the bad guys just keep coming.

Tom Wessels remembers seeing one of the worst, purple loosestrife, being openly sold in this state as recently as the 1980s.

"If people want to see an example of what can happen if an exotic plant gets away and runs wild in the environment, all they have to do is go over to the Potholes, near Moses Lake, and see what happens with purple loosestrife choking the waterways," says Wessels, program manager with the state Department of Agriculture's plant-services division.

Weed seed can hitch a ride in animal feed, fill material or in the folds of your shoes. Even some flowers-in-a-can type seed mixes sold in Seattle have contained seeds of oxeye daisy (Chrysanthemum vulgare), knapweed (Centaurea Biebersteinii) and Scotch broom (Cytisus scoparius) - all outlaws on the state list.

Experts agree that prevention is the most important strategy in this war. If you can't keep a bad plant out, at least keep it from seeding, because depending on the type, weed seed can remain viable for many years. Common mullein (Verbascum thapsus), for example, can germinate after 39 years in undisturbed soil; Canada thistle is good for 21 years. Both of these non-native plants are blacklisted by the state.

A state or federally listed noxious weed is defined as an introduced, non-native plant that is aggressive, highly destructive, competitive and usually hard to control. Their natural enemies were left behind in their native lands. Most of Washington state's noxious-weed species are native to Eurasia.

One of America's most notorious troublemakers, kudzu, is from Asia, where it had been grown for fodder. Once called "miracle vine" and propagated by the millions in the late 1930s by the U.S. Soil Conservation Service for erosion control, it has long been an unwanted pest. By the early 1990s, kudzu had cost landowners $100 million a year to control. It continues to strangle landscape and buildings in several Southeastern states.

Kudzu is noteworthy because it is the Dillinger of bad plants. It is often cited as an example of the worst that can happen when well-intentioned people meddle with nature's balance. We don't have kudzu running wild in the Pacific Northwest, but our gangster plants are just as scary in their own ways.

Washington's varied microclimates provide habitat for more than 100 plants that make up the state's 1998 noxious-weed list - a chart that ranks non-native, destructive weeds according to the seriousness of their threat and the likelihood that infestation can be controlled. All have voracious appetites for real estate.

Purple loosestrife (Lythrum salicaria), giant hogweed (Heracleum mantegazzianum), Scotch broom and Dalmatian toadflax (Linaria dalmatica ssp. dalmatica) were all introduced as ornamentals for home gardens. Many attractive weeds continue to be spread by well-meaning gardeners.

"The most dangerous weeds to us are the ones with ornamental appeal. We're always watching for Scotch broom, knapweed, oxeye daisy, miniature snapdragon (Chaenorrhinum minus), purple loosestrife," Wessels says.

Many noxious weeds not only spread like fury but also cause serious harm. Leafy spurge (Euphorbia esula) has a sap that can burn fingers. Giant hogweed's light-sensitive sap can cause third-degree burns and permanent scarring. Children may be poisoned if they eat the tempting pealike seeds and pods of Scotch broom.

Even some familiar plants, such as St. John's wort (the Eurasian perennial weed Hypericum perforatum), can cause serious problems. The dairy industry in California had such a bad time with this plant several decades ago that banks wouldn't make loans to dairy farmers who had St. John's wort on their land. Cows would eat the plant, it would make them photosensitive, they would blister, develop infections and sometimes die, says Bridget Simon, education specialist for the Washington State Noxious Weed Control Board.

Similarly a little bit of tansy ragwort may not hurt a grazing animal, but an infestation in a pasture spells trouble. Horses eat too much and it can poison and kill.

"It gets your attention when horses begin to die," says Greg Haubrich, weed specialist with the state Department of Agriculture in Yakima. Humans are not immune. Eat a lot of honey made from tansy-ragwort blossoms and you can get tansy in your system, too, and there is a history of liver problems with this plant, says Simon.

And then there's Scotch broom. It may not kill animals directly, but it engulfs habitat and eliminates food-producing native vegetation.

"Scotch broom has no worthwhile place in our ecosystem," says Wessels, who's most desirous of keeping this aggressive plant on the west side of the Cascades. For those who are tempted to plant it, he instead recommends forsythia, which has striking blooms and remains attractive when blooms are finished. Beautybush, too, is much more appealing to the eye and could fill a similar place in the garden.

What else can we do to keep bad plants at bay?

"We don't need to go so far as to discourage ornamentals," says Catherine Hovanic, administrative assistant for the Washington Native Plant Society. "But there are wonderful native plants for the garden that can thrive in our climate of wet winters and dry summers" and have their niche in the ecosystem.

"It is always something of a guessing game when ornamental species are introduced," Hovanic says. Will they be well-behaved? Or will they scramble and smother our native plants, as does Clematis vitalba, the vine with fluffy white seedheads that cloaks Seattle trees in late summer. This plant is not on noxious-weed lists, but it is destructive. It's one of the worst noxious-plant pest in New Zealand, according to Hovanic.

Here are some of the main offenders in Washington state that have made state and King County lists, and warranted inclusion in school curricula prepared by Simon:

-- Purple loosestrife, an aquatic weed from Eurasia that was brought in as an ornamental and in ships' ballast material. It has become established in wetlands across Grant County and is under attack in King County. It produces brilliant magenta-colored blooms that result in 2.7 million seeds per plant. Seeds are tiny and inedible to birds. This plant moves in and replaces native vegetation, creating a biological desert. Birds and mammals have to go elsewhere or die. Root systems clog waterways, bringing increased siltation and flooding and requiring dredging and ditch cleaning.

-- Eurasian watermilfoil clogs waterways used by spawning salmon, boaters and swimmers. Drownings have been attributed to this plant. Lake Washington has had to clear watermilfoil before Seafair to make sure boat props didn't tangle in the weed.

-- Parrotfeather milfoil, with light green, featherlike foliage, is native to South America but thrives in Washington waters. It was sold in pet shops for backyard ponds, lakes and home aquariums. In natural waterways it can clog backwater channels that had been salmon-spawning areas. Dense mats over the surface of the water catch sediment, expand and block access of fish, boats and people. Fragments of the plant stems and rhizomes reproduce. It is very difficult to control: Grass carp won't eat the tough stems; mechanical controls make fragments that cause spreading; a waxy covering keeps herbicides from penetrating.

-- Spartina, or cordgrass, is known as "the weed that ate Willapa Bay." There are three species of non-native spartina in Washington and they are spreading. It has severe impact on tidelands, changing the way water works in the intertidal zone. Spartina traps sediment, causing the shore to gain elevation and wreaking devastating change for migratory waterfowl, shorebirds, bivalves, hardshell crabs, young salmon, English sole and lingcod. Houses on shoreline property become houses in a meadow. Common cordgrass was introduced as a hybrid from England; spartina is native to the eastern U.S. and the Gulf states.

-- Leafy spurge spreads quickly. Sap is irritating and co-carcinogenic, meaning it increases the cancer-causing properties of other substances. In Oregon, lands infested with leafy spurge are reportedly reduced to 10 percent of their original value.

-- Dalmatian toadflax is not toxic but is tough to control, resisting herbicides and spreading by root fragments. It takes over rangeland and pastures and is not palatable to animals.

-- Giant hogweed escaped from Seattle gardens about 30 years ago; toxic sap can leave permanent dark scars on skin. Children have been tempted to use the hollow stems as a spyglass, with painful results.

Dean Stahl is a Seattle writer. Photos courtesy of the Washington State Noxious Weed Control Board. ------------------------------- How to be weed wary

# Inform yourself. Learn to recognize noxious weeds and aquatic plants in your area.

# Be alert when selecting plants for the garden; nurseries sometimes carry invasive plants not on the state quarantine list. Consider using native plants for landscaping.

# Don't transplant any plant if you don't know what it is.

# Don't dump aquarium material in waterways; inspect boats and equipment for plant fragments while at the boat ramp.

# Check your clothing, boots and gear for weed seeds before leaving for the woods, and stay on established roads and trails.

# Avoid hiking through or camping in weed-infested areas. Camp only at existing campsites.

# Pull small infestations of known weeds you see on hikes or other outdoor excursions. Bag and pack out seed-producing parts of plants to keep dry seeds from spreading. Dispose of seeds in a landfill or burn them.

# If using horses in back country, feed stock certified weed-seed-free hay several days before and during your trip.

# Brush animals before and after back country trips to remove weed seeds.