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Ada County working to kill an invasive grass before it spreads into the Boise foothills

A patch of cogon grass, a tall grass with seed tassels, in the Boise foothills
Barbara Ertter
Botanist Barbara Ertter found this patch of Cogon grass in the Boise foothills, now Ada County is working to eradicate this noxious weed.

BotanistBarbara Ertter was hiking in the Boise foothills during the pandemic when she saw a plant that looked like it was “potentially going to jump the fence.”

“It had all the characteristics of something to be worried about,” she said.

She took a sample and with the help of fellow scientists, the tall, green rather nondescript grass was identified as Cogon grass, scientific name: Imperata cylindrica.

“It's just a super aggressive thing,” she said.

If it finds the right environment, she explained, “It could really take hold and crowd out everything else and then it could grow and become more fuel for fires.”

The plant’s rhizomes, underground stems that can sprout new plants, make it hard to control.

“It's a perennial grass with a really robust rhizomatous structure. So it spreads with its roots and then it also spreads by seed,” Schroeder said.

Non-native plants and animals show up all the time in places they shouldn’t be, but some of them can spread aggressively and threaten the local flora. Cheatgrass and goatheads have long vexed the West, but more and more invasive species are cropping up, making it harder for native plants to compete for territory.

“We're seeing a disturbing trend here in Ada County,” said Adam Schroeder, director of the county’s Weed, Pest and Mosquito Abatement department, “We are finding at least one new noxious weed species almost every year since I've been here for about five years.”

The Cogon grass in Boise was found in a subdivision and it’s not clear how it got here. The U.S. Department of Agriculture lists it as one of the most invasive weeds in the country. Ada County had it listed on a temporary state list for noxious weeds, which allowed the county to start killing it.

“We've treated the infestation twice with a glyphosate product, a Roundup type product,” Schoeder said, “And then we're monitoring the results.”

He’s confident they can eradicate this instance of the grass, but as more species get trafficked here, Ertter says it’s humans’ responsibility to try to make room for the plants that have existed here for generations.

“We're the ones who caused it and so that gives us not only the right but the responsibility to try to rectify it,” she said.

Schroeder says another way to slow these unwelcome plants is to be aware when you travel.

“If you're recreating in other areas outside of Idaho or even outside of the county that you live in, make sure that you're cleaning off your boots, you're cleaning off your recreational vehicles,” he said.

Plants and seeds can also hitch rides with pets, so Schoeder says to make sure they’re also cleaned after traveling to new areas.

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