7 Worst Weeds of the Gorge

7 Worst Weeds of the Gorge
Garlic mustard, Alliaria petiolata. (Photographer: Laura Berman)
By Erin Middlewood

When you pull a few weeds in your yard, next thing you know, more pop up. Now imagine weeding the entire Columbia River Gorge.

Agencies on both side of the Columbia River work together to combat invasive plants. These weeds not only threaten the beauty of the Gorge, but also its ecological diversity. They pose a particular risk in the areas still recovering from the 2017 Eagle Creek fire.

"People don't like weeds to move in and change the places they love," said Chris Aldassy, a conservation specialist with East Multnomah Soil and Water Conservation District.

Climate, soils, disease, insects and animals conspire to keep these plants in check in their native territory. But when the seeds stray to new areas without these limiting factors, they spread with impunity.  

"They take over an area, forming a monoculture," said Emily Stevenson, program coordinator for Skamania County's noxious weed program. "We want diversity, with flowers blooming at different times so pollinators have something to eat throughout the season, and fruit for birds and insects."

Most Wanted

We asked weed managers to name the top seven invasive plants that threaten the Gorge.

"We love to debate our weed lists," said Samuel Leininger, the WeedWise Program Manager for Clackamas Soil & Water Conservation District.

Their lists vary because the threats are different from one end of the Gorge to the other. Some invasive plants—herb Robert and Himalayan blackberry, for example—that might have topped the list in the past have become so widespread that weed management agencies don't have the resources to eradicate them by themselves. The agencies instead focus on the ones they hope to prevent from taking root and collaborate with volunteers on the others that are widespread.

"When it comes to managing weeds, you've got some that are pervasive and people see all the time. Then there are the really bad ones," Leininger said. "The early detection species are ones we hope folks never see, but if they do, we have the resources to jump on it right away."

1. Garlic mustard, Alliaria petiolata

Here's one all the weed managers we surveyed agreed is "public enemy No. 1."

Garlic mustard is native to Europe. It thrives in both deep shade and blaring sun. It stands about 2 to 3 feet, with heart-shaped leaves with jagged edges, and small, four-petal white flowers. The weed self-pollinates. A three-foot square of garlic mustard can produce 62,000 seeds, enough to crowd out anything else.

"The seeds are really hard, like little rocks that get stuck in the soles of people's boots," Aldassy said. "Those seeds live in the soil forever."
Worse, garlic mustard is allelopathic, which means it poisons the soil for other plants. The chemicals produced by garlic mustard also hurt the mychorizal fungi, beneficial organisms that attach to roots to help plants absorb nutrients.  

Corbett is the epicenter for garlic mustard in Oregon. Weed managers worry that it will spread.

"We're concerned about it jumping across the Columbia," Leininger said. A hiker who ventures from the Oregon side to Washington could unwittingly carry the seeds on their clothes or boots. Hikers should use boot brushes to prevent spreading garlic mustard. And if they see garlic mustard, they should report it.

"If we know where it is, we can make sure it gets pulled or sprayed," Aldassy said.

2. Shiny geranium, Geranium lucidum

You may well have seen the low-growing, small, five-petal pink flowers of shiny geranium in your yard.
Shiny geranium is native in Europe, Asia and Northern Africa but has become common in Portland and its suburbs. A single plant can produce hundreds of seeds. The seed pods burst with enough force to propel seeds 20 feet, even without wind. Shiny geranium grows in both sun and shade, and can germinate as many as three times in a season.

"It creates these dense carpets," Aldassy said. "They're not going to kill older trees and shrubs, but they crowd other things out over time."


3. Knapweed, Centaurea

Meadow, spotted and diffuse knapweed are all on weed managers' radar. Native to central Europe, knapweed grows anywhere from a few inches to a couple of feet tall with a deep taproot.

Like garlic mustard, knapweed also puts out chemicals that hurt surrounding plants. The leaves are fern-like. Flowers are white, pink or purple and fringed, similar to thistle. Stems, leaves and flowers are covered with hair.

 "That's a pretty nasty species when it shows up," Aldassy said.


4. Hawkweed, Hieracium

Hawkweed grows a foot or two tall and produces yellow or orange dandelion-like flowers. Some varieties are native to the Pacific Northwest, but the invasive kinds came from Europe. Hawkweeds send out runners, which make them quick to spread and hard to pull. They will resprout from any bits left in the soil.  Hawkweed will tolerate a bit of shade, which means they can encroach into forests, but they are more likely to infest meadows. That worries Leininger, who worries about their potential to crowd out the native wildflowers that Gorge enthusiasts enjoy.

"Hawkweed can easily spread through the open grasslands of the Gorge, which we've seen on the eastside," he said. "We're seeing some at higher elevation and on the Pacific Crest Trail."


5. Rush skeletonweed, Chondrilla juncea

Weed managers have all but given up on rush skeletonweed on the eastern end of the Gorge, but are working to prevent its spread west. Rush skeletonweed, native to Eurasia, has a deep taproot, small yellow flowers, slender stems and sparse leaves. Like dandelions, it sends out seeds attached to downy tufts that disperse by wind.

It's hard to fight because "it's almost invisible," Leininger said. "These spindly little things almost look like grass. You'll be on top of it but look past it."


6. Puncturevine, Tribulus terrestris

Puncturevine is native to Europe, Asia, Africa and Australia. It has small yellow flowers. It grows from a taproot to spread almost flat along the ground. Its leaves are oblong and grow opposite each other on a short stalk.

"Its seeds have thorns that will stick in your shoes or puncture a bicycle tire," Leininger said. "It's somewhat rare, although Hood River has a few spots. Mostly it's coming from out-of-area folks." Hikers and other recreationists spread the seeds.


7. False brome, Brachypodium sylvaticum

This hair-covered grass' native range is from North Africa to Eurasia. False brome grows in bunches and usually stays green throughout the year. It grows in both shaded forests and sunny meadows.

"This is one of our big success stories," Aldassy said. Weed managers targeted false brome for early detection and rapid response. A botanist reported seeing false brome in the Gorge eight years ago. Weed managers found it in four locations in the Gorge, including the Eagle Creek drainage.

"We're hopeful for full eradication," Aldassy said. "Fire tends to stimulate false brome, but after the Eagle Creek fire, it doesn't seem to be coming back. Time will tell."


You Can Help

Hikers who spot these villains should take a photo, note the location and contact the Oregon Invasive Species Hotline or the local county’s noxious weed board.

While weed management agencies focus on emerging threats, Friends of the Columbia Gorge leads stewardship work parties for volunteers to tackle the more widespread weeds.

"We can help combat the weeds that agencies don't have the resources to fight. Our volunteers make a difference in protecting the Gorge from invasive plant infestations," said Mika Barrett, stewardship volunteer coordinator for Friends of the Columbia Gorge.

Volunteers may be daunted when they face a carpet of herb Robert along a favorite trail, but they shouldn't be discouraged, Leininger said. "By adopting a site, you can have a meaningful impact no matter what the scale."

Erin Middlewood is a writer from Vancouver, Washington. She enjoys exploring the Columbia River Gorge with her husband and two sons. She's especially fond of the Nancy Russell Overlook at Cape Horn. Follow her at erinmiddlewood.com or @emiddlewood on Twitter.

Above photos;
Garlic mustard (Photographer: Matt Below)
Shiny geranium (Photographer: Bruce Newhouse)
Knapweed (Photographer: Matt Lavin) 
Hawkweed (Photograph provided by King County) 
Rush skeletonweed (Photographer: R. Mueller)
Puncturevine (Photograph provided by Washington State Noxious Weed Control Board)
False brome (Photographer: Glen Miller)