It Seemed Like A Good Idea At The Time: ‘Water wise’ Shrubs Turn Into Invasive Nightmare

Imagine a lovely evergreen ornamental plant that flourishes with little watering even in the driest and poorest soils, spreads with no care and repels deer.

Perfect for gardens in Utah and other arid Southwestern states? That’s what the Royal Horticultural Society opined when it gave myrtle spurge an Award of Garden Merit several years ago.

But what was once billed as a “waterwise” perennial by Utah nurseries has proven to be an eco-nightmare after the plant escaped residential yards and spread into the Wasatch foothills, where it is forming thick monocultures that crowd out native plants, destabilize soils and undermine biodiversity.

Many botanists now consider Utah’s spurge infestation a crisis, but they have few resources to combat its advance. Traits that make myrtle spurge resilient — coupled with a total absence of organisms that prey on it — have turned the plant into an invasive disaster, according to the Utah Native Plant Society’s Tony Frates.

Individual myrtle spurge plants and their seeds are long lived. Seedpods explode in May and propel seeds up to 15 feet, and despite the plant’s toxicity, birds further spread the seeds.

“We waited too long and this thing is now incredibly entrenched, and there just doesn’t seem to be an answer,” Frates wrote in an email. “It seems to be able to grow both in the shade under trees and in completely open places including rock cliffs/crevices. Amazingly versatile. Starts flowering before the bulk of our spring flowering species and gets a head start.”

Known as Euphorbia myrsinites, myrtle spurge is native to the rocky lands of the eastern Mediterranean. Scientists have yet to develop a biological control, typically in the form of an insect or pathogen that co-evolved with the target plant in its native habitat.

“It is possible that the plant could even be a hybrid accounting for extra aggressive vigor,” Frates said, “but no one really knows, and no one is trying to find out that we know of.”

Of Utah’s 3,930 plant species, representing 151 families, some 3,128 are indigenous, while 792 have been introduced, according to Stan Welsh’s “A Utah Flora.” Fifty-three of these nonnatives, such as Russian olive and tamarisk, are on the state’s official list of “noxious weeds,” which sorts them into four categories according to their prevalence and priority for action.

State officials added myrtle spurge to the cast of biological miscreants last year, assigning it to the “prohibited” class, making it unlawful to sell in Utah. But the label otherwise does little to combat the new invader. Some believe authorities should crack down on property owners who allow myrtle surge on their property, as some Colorado communities have done.

“If we are to ever have any chance of eradicating this species, cities need to institute mandatory bans, backed up by fines,” said Susan Sims, a board member of the Utah Native Plant Society.

Resembling big overripe broccoli tops, myrtle spurge blankets some hillsides, especially exposed south- and west-facing slopes above Salt Lake City neighborhoods. The infestations are plainly visible to those frequenting the Bonneville Shoreline Trail.

Hardest hit are City Creek, Emigration, Mill Creek and Neffs canyons, where spurge is proliferating at an exponential rate. The plant now covers the bottom of Dry Canyon above Salt Lake City’s Federal Heights and soon will move up both sides under the gambel oaks toward the ridgetops.

The Utah epidemic likely started in Salt Lake County but has spread into neighboring counties. U.S. Forest Service botanist Mike Duncan has seen myrtle spurge in every canyon he has visited along the Wasatch Front.

“We are tracking it and watching it,” Duncan said, “and where we can, working with partners to treat it.”

In coming weeks, several groups are planning weed-pulling events on affected acreage, timed with the spring when the soils are still damp and before seeds mature. While some observers see these pulls as too little too late, organizers say they play an important role.

Red Butte Canyon, behind Fort Douglas on the University of Utah campus, is among the least-infected areas, probably because it does not abut neighborhoods, and it is the target of regular public weed-pulling campaigns coordinated by employees of the U.’s Red Butte Garden.

“We will go in and pull huge plants and the next year the ground will be carpeted with seedlings,” said botanist Neal Dombrowski, who co-founded Urban Habitat to promote removal of invasive weeds along the city’s foothill interface.

Last year, 222 people participated in six pulls around Red Butte. This year, Dombrowski is hosting eight such events, including one May 24 in the Red Butte Canyon Natural Research Area.

Plants targeted in the weed purges include Dalmatian toadflax, dyer’s woad and houndstongue.

Volunteer teams pull up the plants, which they bag and leave on the ground to allow the sun to break down their contents. Gloves and boots are mandatory for these weed pulls, which are not without their perils. Crews work on steep slopes where a slip can result in a nasty tumble. And when spurge stalks break, they ooze a caustic white sap that can irritate skin and damage eyes.

Adding further insult to injury, myrtle spurge lacks a root network that might otherwise hold soils together. Instead, it has taproots that extend up to 14 feet, making the plants hard to pull out and useless for preventing erosion, according to Duncan.

Yanking up the plants poses a kind of Catch-22: Invasives will recolonize the open ground unless noxious seedlings are plucked out in subsequent years and native flora are planted in the disturbed soil.

“It grows right over the top of other plants, so there is really no way to stop it,” Frates wrote. “I’m not saying we should stop trying, but the outlook is very, very grim.”

Two years ago, U. undergraduate Brianna Milot began studying weed pulls in a research project overseen by the U.’s Environmental and Sustainability Studies Program. She staked out two research plots in Red Butte Canyon, where she documented an abundance of the plant in March 2017 and again this year.

She concluded that pulling out the plants reduces the prevalence of myrtle spurge, but only if an area is treated in following years.

“If we can get the seed heads, we are reducing next year’s crop of myrtle spurge,” Pecchia-Bekkum said. “The more you pull up, the less is there. That means two or three years down the line there is not as much, and it can be controlled.”

Salt Lake County officials declared spurge a noxious weed a decade ago and began a public education campaign.

“We invited people to dig it up and exchange it for native plants, but it didn’t make a dent,” said Sage Fitch, who directs the county’s weed-control program. “The reality is, it is very expensive. It’s valuable for landowners to remove it. It’s a public health threat.”

Today, myrtle spurge can be seen growing in many Salt Lake City yards, often metastasizing into neighboring yards and along sidewalks.

“You really can make a difference by digging it up,” Fitch said. “However, there are areas where I’m hesitant to do that — steep hillsides that have become totally covered. I’m concerned that if it’s removed, they will have problems with erosion. You can do a lot of disturbance.”