Divers prepare to yank irrigation-clogging weed

Flowering rush, an invasive Eurasian aquatic weed, will soon be removed by a diving team from several sites on the Columbia river, where it was discovered last year. The weed poses a danger to agriculture because it can block irrigation canals and irrigation intakes.

Divers equipped with suction hoses will soon begin removing flowering rush from sites on the Columbia river where the irrigation canal-clogging weed was discovered last year.

The invasive species was first found on the Oregon side of the river near McNary Dam in August 2014, but regulatory hurdles prevented it from being dug out immediately.

Flowering rush is already a problem in Washington, Idaho, and Montana, where its thickly growing leaves impede water movement to the detriment of irrigators and fish.

A team of divers from the U.S. Army Corps of Engineers is scheduled to spend the final week of August yanking the plants, which were previously covered with plastic barrier mats to prevent the weed patches from spreading.

“This is going to be an ongoing thing for a while and there are no easy solutions,” said Tim Butler, noxious weed control program manager for the Oregon Department of Agriculture. “Unfortunately, there are no silver bullets. It’s a difficult plant to control, is the bottom line.”

Before divers were allowed to physically pull the weed, the U.S. Army Corps of Engineers — which has jurisdiction over the Columbia River — had to clear the project under the National Environmental Policy Act, the Endangered Species Act and the Archaeological Resources Protection Act.

With that process complete, further removals will not have to be evaluated under NEPA or ESA, though new sites will still have to be reviewed for cultural resources under ARPA, said Damian Walter, wildlife biologist for the agency.

The upcoming diving project is expected to cost $50,000, which required the agency to shift funds from other invasive management programs, he said.

Flowering rush remains submerged during winter, so the diving team also had to wait until the plants were at their most visible to begin removal, Walter said.

The weed is a concern for irrigators because it can stop water from freely flowing in canals, hindering water delivery. Its capacity to change ecosystems is also a risk for threatened and endangered native fish, as the plant creates the ideal habitat for invasive pike that prey on them.

Treating the weed patches with herbicides is troublesome because of the plant’s aquatic nature — chemicals are difficult to effectively apply in flowing water, can damage crops and face environmental restrictions.

“The physical removal is probably the best technique we have at this point,” said Butler.

In the long term, researchers from Washington State University hope to identify natural predators in Central Europe, where the weed originates, to help suppress it in the Northwest.

At this point, two potential candidates have been found: the beetle species Bagous nodulosus and Bagous validus, which feed on the flowering rush’s rhizomatous roots, said Jennifer Andreas, director of WSU’s Integrated Weed Control Project.

Attacking the rhizomes is important, since fragments break off and allow the weed to infest new areas downstream, she said. “That’s the part that’s causing the biggest damage. That’s the part that moves.”

Before the insects could be released into environment, researchers must conduct extensive studies to show they would not damage native plant species, Andreas said.

Approval must come from the USDA’s Animal and Plant Health Inspection Service and the process usually takes about a decade, she said.

Biological controls are typically deployed against invasives that are already widespread, but WSU hopes to release a natural enemy before flowering rush gets completely out of control, Andreas said.

“This is a weed that is spreading incredibly quickly,” she said.

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