At first glance, the delicate yellow flowers appear rather pretty. But glance up, and you realize the plant’s green leaves and branches stretch all the way to the horizon, blocking out most everything else. In just two weeks, this green monstrosity has doubled in size, growing into a thick, dense mat on the shoreline along Bybee Lake and into the water.
What is ludwigia?
Invasive ludwigia is an aquatic plant native to South America. Officials in Oregon started noticing a dramatic growth in ludwigia about five to seven years ago, likely after people dumped out aquariums with ludwigia in local waterways.
Ludwigia has several species and subspecies of ludwigia. Most of the ludwigia found along Willamette River backwaters is Ludwigia hexapetala, sometimes called water primrose or primrose willow. The kind found at Smith and Bybee Wetlands is Ludwigia peploides montevidensis. Ludwigia peploides is sometimes called floating primrose willow.
One kind of ludwigia is native to Oregon – Ludwigia palustris – but the plants are much smaller than the invasive varieties, and they do not compete with other native plants. The native ludwigia is sometimes called eastern false loosestrife or marsh seedbox.
This is invasive ludwigia, an aquatic plant native to South America that is threatening to choke backwaters, oxbow lakes and warmer river channels in Oregon. Ludwigia could destroy these special habitats and harm water quality, damaging native plants, amphibians, fish, birds and other wildlife. But it’s not too late to avoid the worst, and a network of groups is battling ludwigia, including Metro at Smith and Bybee Wetlands Natural Area in North Portland.
Ludwigia is the worst invasive aquatic plant in the state, said Glenn Miller, an invasive plants specialist at the Oregon Department of Agriculture.
“As I say to people in lectures, this one is the game changer,” he said. “It is so impactful that you’ll see open bodies of water that just convert to anaerobic mudholes in probably 20 years and really exclude most other life. No other aquatic plant we have had in the state does that.”
State officials first noticed a significant increase in invasive ludwigia about five to seven years ago when it started infesting Willamette River backwaters, such as Delta Ponds in Eugene. Since then, there have been infestations at Willamette Mission State Park near Salem, near Willamette Falls, Smith and Bybee Wetlands and other parts of the Willamette River system. Infestations have also been spotted in the Columbia Slough in Portland, Rogue River system in southern Oregon and in Central Oregon.
“The entirety of western Oregon and up through the Columbia River system and some parts of central and northeastern Oregon could be really susceptible to it,” Miller said.
Experts suspect ludwigia arrived in Oregon through the aquarium and aquatic garden trades. The plant is popular in aquariums, which often get dumped into local waterways when people no longer want them.
Ludwigia has completely infested a side channel at Black Dog Landing near Albany. Photo by Travis Williams
Devastating impacts
Ludwigia has the potential to devastate aquatic ecosystems.
“You’d most likely see a decline in the native populations of turtles, amphibians and fish in the Willamette and Rogue systems,” Miller said. “These are unique habitats that were formed when the river meandered, and we’re losing them.”
Help tackle ludwigia
Interested in joining the fight against invasive ludwigia?
Please clean, drain, and dry boats and gear after all outings on water.
If you spot invasive ludwigia, report it to the Oregon Invasive Species Hotline.
Join the Willamette Aquatic Invasives Network and contribute to a community map of ludwigia.
Native plants form the basis of healthy habitats that provide food and shelter for native animals. For instance, Smith and Bybee Wetlands is an important stopover for migratory birds to rest and refuel as they fly to and from the Arctic. But when invasive ludwigia covers an area, migrating shorebirds can’t stick their beaks in mudflats to eat bugs, and wintering ducks and waterfowl find less rice cutgrass and other native seeds and plants.
Ludwigia can also lead to poor water quality, said Elaine Stewart, a senior natural resources scientist at Metro. The dense mat of ludwigia on the water surface and decomposition as it dies deplete oxygen from the water. Low oxygen is bad because native fish and invertebrates that live in the wetlands need oxygen. It could also make water quality bad for salmon.
“Ludwigia can throw an entire ecosystem out of balance,” Stewart said. “Complexity is good in an ecosystem, and ludwigia simplifies it.”
A network of people is trying to prevent that from happening in the Willamette River system. Formed in 2014, the Willamette Aquatic Invasives Network meets quarterly, and members represent more than 60 government agencies, land trusts, nonprofits, universities, businesses and community members.
The network is forming a steering committee to develop a comprehensive aquatic invasive species action plan, said Marci Krass, the network coordinator and restoration program manager at the nonprofit Willamette Riverkeeper.
“There’s a lot of enthusiasm in helping to save these backwater habitats,” said Matt Mellenthin, a network member and a habitat restoration coordinator at Integrated Resource Management, a company based in Philomath. “Just about everybody in the environmental field clearly sees how important the habitats being taken over by ludwigia are. Whether it’s for salmon rearing or water quality, there are just a lot of partners working on this stuff together.”
Metro has hired Mellenthin’s company to help control ludwigia at Smith and Bybee Wetlands – and it’s not the only one.
“The first year we worked at Delta Ponds (in Eugene), it was the first large-scale ludwigia treatment in Oregon,” Mellenthin said. “In a five-year span, we’ve gone from one project to 13 large projects throughout the Willamette Valley, from Eugene to Smith and Bybee.”
Invasive ludwigia can also significantly reduce recreational opportunities. Infested areas often cannot be accessed by motorized or nonmotorized boats.
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Small fragments of ludwigia can easily spread and grow, causing new infestations downriver.
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Ludwigia peploides montevidensis leaves can appear more pointed when growing on land.
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Ludwigia hexapetala leaves can appear more rounded when growing on water.
Protecting Smith and Bybee Wetlands
Seemingly hidden among industrial warehouses in North Portland, Smith and Bybee is one of the largest urban wetlands in the country. At nearly 2,000 acres, the natural area is home to beavers, river otters, black-tailed deer, western painted turtles, blue herons, osprey, bald eagles and many other animals. It’s also a popular paddling destination in the winter, and people walk the trails year-round.
Metro staff first spotted invasive ludwigia at Smith and Bybee Wetlands in the mid-2000s, said Justin Cooley, a natural resources technician at Metro who has coordinated the efforts to control ludwigia. Metro and Portland State University experimented with control efforts beginning in 2010.
Large-scale treatments started in 2014, thanks to money from the parks and natural areas levy approved by voters the previous year. In 2014 and 2015, intense treatments from July through September helped keep ludwigia under control. In 2016, crews faced their biggest challenge, tackling a 60-acre monoculture that had developed on Bybee Lake. The goal is to contain ludwigia and prevent it from spreading further, but it’s unlikely that it will be eradicated.
“We are doing everything we can to try to get this down,” Cooley said. “Right now we’re at a point where we can manage it.”
The fight isn’t easy. Ludwigia is hardy and stubborn. It typically starts growing along the shorelines and quickly makes its way into lakes and rivers.
“It’s an early colonizer as the mud flats are exposed,” Cooley said. “It can outcompete any of the native plants, such as the forbs, sedges and rushes.”
Ludwigia will spread on the surface of the water, and parts of the plant will drop down. Eventually the roots are attached to the bottom of the lake or river. Special roots even feed oxygen to the plant in low-oxygen environments.
Each year, contractors start by hand pulling and spraying a glyphosate-based herbicide on ludwigia growing around the lake. The first round of treatments usually occurs in late June using canoes to reach floating mats away from the water’s edge. The herbicide prevents floating mats of ludwigia from taking root on the lake bed as the water level drops, ensuring migrating birds will have access to open water and mudflats to feed on native plants.
As new plants grow on the exposed lake bed, crews strap on 4½ gallon backpack sprayers and walk around to treat the ludwigia. At the height of the growth, crews use a 700-foot hose connected to an ATV to reach patches far from solid ground.
“It is tiring work,” Cooley said. “The crew is wearing chest waders and slogging through mud.”
Herbicides are the most effective method of treating ludwigia, especially on a large site, but they’re used with caution. The weed killer used to treat ludwigia is approved by the Environmental Protection Agency for use in and near water.
Hand pulling ludwigia is not feasible as the only tactic at a large site like Smith and Bybee Wetlands. It must be done with care, since hand pulling can spread ludwigia, which easily grows new colonies from small fragments that break free and float away. It also spreads by seeds.
Come June, another round of treatments at Smith and Bybee Wetlands will start in the ongoing effort to control ludwigia.
“I’m hopeful we’ve turned the corner and are pushing ludwigia down,” said Stewart, the Metro scientist. “Invasive species are forever. It takes a lot of resources.”