Himalayan blackberries are one of the most resilient invasive species that Metro has to manage at its natural areas.
As Metro's Natural Areas Land Manager, Dan Moeller is a veteran in the war against invasive weeds. At times, the battle seems one-sided: Just when the garlic mustard is cleared from one property, a patch of false brome is found on another.
But when Moeller speaks of Rubus armeniacus, commonly known as Himalayan blackberry, it's with grudging respect.
"You can look at it and say, 'It would be great to get rid of it.' But we also look at in awe." Moeller paused, then emphasized each word. "Because it is so good at what it does."
Himalayan blackberry (and the equally noxious Evergreen blackberry, Rubus laciniatus), is the poster plant of invasive weeds – a pest so aggressively successful that it can grow from a single plant into an impenetrable thicket in just a few years.
Autumn is the season that agencies and property owners often are out trying to control blackberries, as part of a systematic approach that includes cutting or smashing the canes in the summer, then spraying pesticide on the new canes to limit new growth in the spring.
Most Northwesterners are familiar with the Himalayan blackberry. They've enjoyed its juicy sweet fruit, or cursed its tearing, sharp thorns. Because it's such a part of our landscape, rural and suburban, many assume it is a native species.
The Himalayan blackberry was introduced to Oregon as a crop plant sometime in the late 1800s and quickly escaped. The weed was remarkably successful, thanks to the birds and wildlife that spread its myriad seeds and to its ability to root from the tip of its canes or from mere fragments of roots.
Some property owners even planted the weed, believing it would control erosion along streams.
"When we buy natural area property, and even agricultural land, in certain places where there's been disturbances, you can find almost a monoculture of blackberries," Moeller said.
As it spreads, the blackberries push out native plants, including our native trailing blackberry, with its long, slender vines and intensely flavored fruit. Nothing can grow beneath the thickets, which can lead to erosion. And the blackberry roots are not that good at stabilizing banks. The thickets provide food and habitat for some species, but not for the full diversity of animals and birds that depend on native plants.
Humans also feel the effect of blackberries and other noxious plants.
A report to the Oregon Invasive Species Council found that the state's 21 "noxious" species caused $125 million in production loss, fire damage and other control costs. The cost of noxious weeds to the United States in general tops an estimated $143 billion, according to the report.
Volunteers help clean up Himalayan blackberries at Howell Territorial Park on Sauvie Island.
Getting rid of blackberries is neither easy nor quick.
"We don't go in and treat the weed until we can commit to coming back multiple times," Moeller said. "You can't assume that you can go in once and take care of a weed, any weed. There's a high chance the weed will come back. In the soil, there's a seed bank that's grown over the seasons."
Property owners with small infestations should dig out the root ball – and have the shovel ready when the weed, invariably, rises again. Spraying new growth with a pesticide can be effective. Just remember that blackberry roots have been found more than three feet deep and spreading more than 30 feet, and that any root pieces left in the ground likely will grow.
County offices of the Oregon State University Extension Service are good sources for advice, as are the local offices of the Oregon Soil and Water Conservation Districts.
Large tangles of blackberry typically are mowed or flattened, and then sprayed. The tactic is repeated until the weed is under control, which with blackberry doesn't necessarily mean complete eradication, Moeller said.
Blackberry control work is underway at Metro's Clear Creek natural area south of Carver. The property was once used for Christmas trees and its mature riparian forest, prairie and stream banks were overwhelmed by Scotch broom and Himalayan blackberry.
The entire property was mowed and treated. Moeller said the work will be repeated until the weeds are controlled.
Eventually, more than 500 acres will be returned to native species. The natural area will include a rare wetland prairie, one of the few left in the Willamette River valley, and the stream with the most abundant salmon population in the lower Clackamas River basin.
Fighting blackberries now to restore such a treasure for the future is worth the battle, Moeller said.