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Poisonous mushroom found in Boise neighborhood

The mushroom, known as "Death Cap," was found in the North End. Idaho Health and Welfare said it may be present elsewhere in Idaho.

BOISE, Idaho — Editor's note: This story originally appeared in the Idaho Press.

A mushroom never before detected in Idaho is popping up around Boise.

But be warned: You don't want to chop this one up and throw it in your stir fry.

Amanita phalloides, also known as the "death cap," has been found on Harrison Boulevard in Boise's North End, according to Mickey Myhre, a retired physician and current mycologist. The Idaho Department of Health and Welfare later said the mushroom was found under an oak tree "in an established neighborhood in Boise." Myhre said the mushroom has also been found "in some locations in the North End."

It's highly poisonous and responsible for more than 90% of mushroom poisoning deaths worldwide, according to the Centers for Disease Control and Prevention.

You won't get sick from touching the fungi. But if it's ingested, the death cap causes flu-like symptoms, before a brief reprieve provides false hope and precedes organ failure, specifically the liver and kidneys. Death can occur 7-10 days after ingestion.

On average, one person a year has died in North America from ingesting death caps, though that number is rising as the mushroom spreads, The Atlantic reported in 2019.

The death cap is native to Europe, but has spread to several continents, and likely reached North America "many decades ago," according to the British Columbia Centre for Disease Control.

A spokesperson for the Idaho Department of Health and Welfare confirmed to the Idaho Press that Amanita phalloides has been identified in Boise. "It may be present and undetected in other places (in Idaho) and it may not be," the spokesperson said.

The department encourages anyone who believes they found a death cap on their property to dispose of it in the garbage, not their yard debris can or compost pile, and to clean and disinfect any gardening tools, gloves or clothing that touched the mushroom.

The mushroom is also deadly if eaten by dogs, the spokesperson said.

Anyone who believes they found a death cap can take a photo and upload it to inaturalist.org, where they can discuss their findings with fellow naturalists. Additional information is available at the Southern Idaho Mycological Association's website, idahomushroomclub.org, and the North Idaho Mushroom Club Mycological Association's Facebook page.

Death caps' journey to Idaho

How did it end up in the City of Trees? Most likely, via the trees.

Myhre, the retired physician-turned mycologist, said some of Boise's trees are transplanted from Northern California, Oregon, Washington and British Columbia, all locations that have been infected by death caps.

The fungus lives in and around the trees' roots, Myhre said.

"The trees that we have here lining our yards and boulevards were largely imported from West Coast sources, mostly Oregon and Northern California. So it's not a matter of if, it's a matter of when this mushroom will show up," Myhre said. "Once a tree is transplanted that carries the fungus, it can take 60 years to produce a mushroom. It's been about that long since a lot of the older trees in the city have been planted."

When he was a doctor, Myhre's titles included chairman of the Saint Alphonsus pathology department, president of the Ada County Medical Society, president of the Idaho Medical Association and owner/founder of Idx Pathology. Since retiring, he's taken an interest in mycology — the study of fungi — and is a member of the Southern Idaho Mycological Association. He and his wife are booked for a trip to Nepal, where they'll work with fellow mycologists to find mushrooms that have yet to be identified on their way to Mount Everest's south base camp.

At a Southern Idaho Mycological Association meeting in September, a fellow member presented Myhre with mushrooms she found on Harrison Boulevard that bared a close resemblance to death caps. But the only way to know for sure was to perform a DNA analysis.

So, Myhre set up a DNA barcoding lab.

"When we ran the Amanita phalloides DNA through, it came trough as a 99.85% match," Myhre said.

Dos and don'ts

"The No. 1 rule with any kind of mushroom is don't eat anything unless you're absolutely sure of what it is," Myhre said.

Death caps look similar to the paddy straw mushroom used extensively in Asian cuisine, Myhre said. But you likely won't find those in Idaho. Additionally, cooking or freezing death caps won't eliminate their toxicity.

If you see one, dig it out of the ground by its stalk.

It's important to note, Myhre said, that no eradication method has worked. Spraying fungicide or other pesticides on death caps won't kill them.

"Death cap mushrooms are found near imported trees in gardens, parks, and urban areas but can spread to wild areas over time," according to a release from the Department of Health and Welfare. "In other regions, death cap mushrooms appear in late summer through December, or year-round. Seasonal risk in Idaho is unknown."

What to do for potential mushroom poisonings:

  • If you or your child has eaten an unidentified wild mushroom, immediately call the poison center at 800-222-1222, call your healthcare provider, or go to the emergency room.
  • If your pet has eaten a wild mushroom, call the ASPCA Animal Poison Control Center's 24-hour hotline at 888-426-4435 or contact your veterinarian or local veterinary emergency clinic.

What to do if you find a wild mushroom in your yard:

  • To help avoid spreading death cap mushrooms to other areas, remove the mushrooms from your lawn before mowing. Grasp the mushroom low on the stalk and pluck it from the soil.
  • There is no evidence that hand contact with death cap mushrooms is dangerous, but wearing gloves will protect your skin from germs in the soil.
  • Wash your hands thoroughly after touching the mushrooms or surrounding soil.
  • Dispose of the mushrooms in the garbage. Do not compost at home or put in the city compost cart. Do not put death cap mushrooms in wood chip containers or trucks.
  • Clean and disinfect garden tools after using them around affected trees.

This article originally appeared in the Idaho Press, read more on IdahoPress.com.

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