Carrizo cane is the border wall no one wants.

A pernicious plant on the banks of the Rio Grande along the U.S.-Mexico border, carrizo cane (Arundo donax) grows as much as 30 feet tall and so thick that people entering the country illegally can easily hide in it. Border patrol officers can’t see into it. Infrared signals can’t penetrate it.

Its roots form in clumps that can spread for hundreds of feet and choke out native vegetation. It sucks up water to fuel its growth—up to seven inches per week—affecting the river’s flows and using up drinking water and water for livestock.

“We have different missions, but we have the same goal, which is how do we control this invasive,” Tricia Cortez, executive director of the Rio Grande International Study Center, an organization dedicated to protecting the Rio Grande watershed, told Bloomberg Environment.

Cost Comparisons

The need to control carrizo cane is a rare element of border security that Republicans and Democrats agree on. Committing to doing it is another.

Last week’s $321 billion government spending and border security package only provided $1 million to address the hundreds of miles of cane along the river. U.S. Customs and Border Patrol has estimated it would cost $2.75 million per mile to dig and replace it with native vegetation.

It costs between $3,600 and $105,000 per mile to cut the cane and control its growth with herbicides or cane-eating insects, according to the Texas State Soil and Water Conservation Board.

Other initiatives to create a carrizo cane control program, usually tucked into a larger bill, have failed.

In 2015, the Texas Legislature directed the state Soil and Water Conservation Board to eradicate the reed but didn’t specify how to get rid of it.

The Texas Legislature has said $4.9 million per year is necessary to chop the cane down, apply herbicides, deploy wasps and other insects, and plant native vegetation in only the most ecologically disturbed areas. The state’s carrizo control program only receives a fraction of that: $1.5 million per year.

Threat to Border Security

Environmentalists prefer a long-term plan that would rip out the cane and its knotty network of roots and replace it with native plants, or to cut down the cane and use insects to eat the roots.

Border agents want to clear the cane to improve visibility as quickly as possible, including spraying with herbicides if necessary.

“It impedes our ability to see people coming across,” said Chris Cabrera, an agent in McAllen, Texas, and spokesman for the National Border Patrol Council. “The potential for one of our agents getting attacked by someone in there is pretty great.”

While most of the news on the border centers with President Donald Trump’s plan to build a border wall, attention to carrizo cane control fell by the wayside.

“With all due respect, people don’t understand carrizo cane,” Rep. Henry Cuellar (D-Texas), one of the bill’s negotiators, said after the House’s passage of the border security bill.

Cuellar, who made photos of the weed a central prop in border security hearings, said he plans to ask for more money to cut and slow the growth of cane for the next fiscal year, although he declined to say how much.

‘Never-Ending Treadmill’

Rep. Kay Granger (R-Texas), the ranking member of the House Appropriations Committee who also negotiated the package, agreed that more support is needed.

“Cuellar made a very strong case,” Granger said, but “it’s all we can do this year.”

Cuellar’s district covers about 200 miles of the border, including the town of Laredo, whose local government is fighting a border wall with a proposed riverwalk and flood control plan that incorporates planting native vegetation along the river’s banks.

The standard approach for keeping the cane under control is cutting it down to three feet twice a year and treating it with herbicides. While this is the simplest method, chemical control is controversial with residents and only provides short-term relief.

“It can be kind of a never-ending treadmill to keep it mowed down to a height that works for border security,” David Yeates, CEO of the Texas Wildlife Association in San Antonio, told Bloomberg Environment.

In 2009 a local Laredo neighborhood association sued and successfully halted Customs and Border Protection from spraying herbicides from a helicopter to kill off carrizo cane.

While herbicides have a role in successfully managing the cane quickly and cost-efficiently, they can also hasten erosion of the river banks and threaten wildlife, according to the Customs and Border Patrol’s assessment.

Push for Restoration Program

Another solution is using insects. Customs and Border Protection, the Homeland Security Department, and the Agriculture Department launched a program in 2009 to control the cane using Spanish arundo wasps and scales—small insects—that suppress growth by feeding on the roots of the cane.

But it can take years to see initial results. It took seven years for the amount of carrizo cane to decline 32 percent after wasps were deployed between Brownsville and Del Rio, Texas, in 2009. It would take about as long to remove the cane and replant it.

The National Wildlife Federation lobbied Cuellar’s office and others to include language in the border funding bill to completely eradicate carrizo cane and salt cedar—an evergreen tree that also takes up water and obscures visibility—and replace them with native plants.

The price tag: at least $250 million, according to the NWF’s proposed amendment to the border bill.

Collin O’Mara, the National Wildlife Federation’s president and CEO, would like to see the creation of a Rio Grande restoration program to which lawmakers could direct money in the next appropriations cycle.

“We’re trying to make sure we’re making the case for folks to understand why this is an extremely cost-effective solution to multiple problems,” O’Mara said.

But offering hundreds of millions to eradicate a weed that hardly registered a pulse during the border wall debate could be a tough sell.

“It might be a little high,” Cuellar said of the number. “We want to do miles and miles and miles.”