A new invasive plant has taken root in Oregon for the first time. The Oregon Department of Agriculture confirmed that Hydrilla verticillata had been found on private property in Jackson County in October.

The aquatic weed grows long, slender branches with serrated leaves, which together form a thick mat of vegetation that can block waterways and take over native ecosystems.

“It’s widely regarded as the worst invasive weed in the world,” said Troy Abercrombie, the program manager who oversees the Oregon Department of Agriculture’s noxious weed control and native plant conservation. “It’s one of very few federally listed noxious weeds.”

Abercrombie said it’s a best-case scenario, as the Hydrilla verticillata, which likes to grow in freshwater, has been caught early on and is isolated to small ponds. In Oregon, the plant is listed as an A-rated invasive species, meaning it isn’t widespread and can be targeted for eradication with herbicide.

The department is now consulting with experts from Florida, a state that has spent hundreds of millions of dollars in the past decade managing the persistent weed, according to Abercrombie.

Hydrilla verticillata, which is native to tropical regions in Asia, Africa and Australia, was at first used as an ornamental species for aquariums because of its vibrant green color and elegant stems. But as the plant made its way into the wild, its spread became uncontrollable.

Dense mats of the weed can be nearly impenetrable to boats and swimmers, and they block the movement of aquatic organisms. In some cases, its proliferation can even change the hydrology of a river as it slows water flow and causes organic matter and soil to build up.

“You can have these cascading effects where the eventual impact is much larger than the singular impact from the species itself,” Abercrombie said.

Samuel Chan, an expert on watershed health at Oregon State University, serves on the Oregon Invasive Species Council. He said there are several reasons why Hydrilla verticillata, or water thyme as it is commonly known, is so difficult to manage.

“It’s a species that in my whole career, I’ve never seen spread so fast,” Chan said. “It grows at least 1 inch a day.”

Chan said Hydrilla verticillata is extremely adaptable because of its varied methods of reproducing — it can sprout from tiny fragments or dormant buds.

“ODA can treat the vegetative part of it with herbicides,” Chan said. “However, those turions and tubers will stay in the sediment.” Those dormant buds could easily sprout again next season, so eradication efforts require years of vigilance.

Abercrombie is asking the public to keep an eye out for Hydrilla verticillata by reporting any sightings to the site oregoninvasiveshotline.org.

News Source : https://www.opb.org/article/2026/11/11/invasive-aquatic-weed-hydrilla-verticillata-found-in-oregon-for-the-first-time/