October’s Weed of the Month: Himalayan Blackberry

Himalayan blackberry (Rubus armeniacus) tantalizes us with its sweet fruits in the summer and tortures us with its prickly vines all year long. Also known as Armenian Blackberry, this wide-spread and aggressive weed is native to Armenia and Northern Iran. It is considered an invasive species in many parts of the world, including here in Clackamas County.

Recursive Blackberry thorns

In Oregon, Himalayan blackberry is considered a more common Class B noxious weed. It is found in much of western Oregon and is not actively surveyed, even though it is a weed of economic importance. As a class B noxious weed, propagation, transport, and sale of this plant are prohibited by law.

One can find Himalayan blackberry throughout Clackamas County. It thrives on unmanaged sites, disturbed areas, and along stream corridors. Due to the spread of seed by birds, it is also commonly found under perching sites, such as along fence rows and under power lines.

Himalayan blackberry is a tall, semi-woody shrub with thorny stems and edible fruits. It grows upright on open ground and will climb and trail over other vegetation. Mature plants can reach up to 15 feet in height. The canes of Himalayan blackberry can reach lengths of 40 feet and are typically green to deep red in color.

Himalayan blackberry forms dense, nearly impenetrable thickets of brambles. In some instances, canes can reach densities of more than 500 canes per square yard. Canes typically last only three years before dying off, so dense thickets are often dominated by old canes.

Why Should I Care About Blackberry?

Himalayan Blackberry

The removal of blackberry from public and private property is an ongoing battle. The plant aggressively reproduces by seed which passes undamaged through the digestive tract of many birds and animals and can remain dormant in the soil for several years. The canes of adult blackberry plants will also root where the tips touch the ground. Roots may reach 30 feet in length and extend 2-3 feet deep. Unfortunately, even small root fragments can develop into new plants.

Management of this invasive weed requires the investment of significant resources in time, equipment, labor, and herbicides. In the case of agricultural land, infestation by blackberry can reduce the available land area for farming and significantly increase farming costs. Addressing any invasive weed increases farm costs that are then passed on to consumers in higher food prices.

Habitat for wildlife is also disrupted when blackberries form dense thickets that crowd out many native plants. Many of these native trees and shrubs provide shade and bank stability along rivers and streams. In forest land, older canes can build up a substantial litter layer which may serve as fuel for wildfires.

How Can I Control Blackberry?

Blackberry Bramble

Autumn is an ideal time to manage Himalayan blackberry on your property.  During the spring and summer months, birds and small mammals often use the thorny brush to build nests to protect their young from predators. Blooms attract pollinators and berries are attractive to people, birds, and other animals. Desirable plants that co-exist with blackberry are also actively growing during the spring and summer months, so control activities on blackberry during this time can be potentially harmful to them as well.

In the fall months, our native plants have largely died back or become dormant for the season, young birds have fledged, and the blackberry flowers and fruits are no longer attracting wildlife. At this time, blackberry plants are also reallocating their resources down into their roots, making fall the ideal time to manage these plants with a targeted herbicide application. Should you choose to use chemical control, ALWAYS FOLLOW THE LABEL and put safety first, for you and any unintended targets.

For manual control, it is important to arm yourself against the sharp thorns by wearing thick gloves, sturdy long pants, and long-sleeved shirts or jackets. Those who are unprepared will suffer the consequences with nasty scratches. Use a board or plywood to mash down blackberry canes to access densely infested areas. If your ground is level or has little to no slope, you may also be able to mow down the canes (sometimes a brush cutter is necessary). This will remove the bulk of the plant.

Fruiting blackberry

If you wish to use the mowing method for permanent control, you will need to repeat this process throughout the year and for several seasons to exhaust the energy in the root system. Remember to check for any nesting birds in the spring. Should you choose to use goats to remove the blackberries, you may still want to get rid of the old canes first and then let the goats periodically graze the new growth for long-term control.

If you choose to remove the entire plant, including the roots, you will have much easier access with the top growth removed. Digging or tilling can take out the root system, but be sure to remove as much root material as possible. Even small pieces can re-sprout, so try raking up all remaining bits. If you are working on a slope, make sure you have enough time in the fall to reseed any disturbed areas to avoid erosion caused by fall and winter rain. If not, root removal might need to wait until spring.

After blackberry is removed, expect a flush of weeds in the old blackberry patch. A build-up of weed seed may remain dormant under the brambles for years and once exposed to sunlight they will sprout.

Removal of invasive blackberry requires persistence and patience, but success comes to those who persevere! For more detailed information on blackberry control, check out the Best Management Practices for Himalayan Blackberry. If you have specific questions about Himalayan blackberry contact the WeedWise program.

If You Like the Berries, Plant a Native Instead!

Western thimbleberry (Rubus parviflorus)

Pacific blackberry (Rubus ursinus), also known as trailing blackberry, wild mountain blackberry, or Northwest dewberry is the only blackberry native to Oregon. Its smaller, sweeter berries have fewer seeds and ripen earlier than Himalayan blackberries. Instead of forming huge brambles, these plants trail along the ground and can sometimes be found in areas that have been recently logged or burned.

Thimbleberry (Rubus parviflorus) is another great native berry with delicious fruit prized by foragers. The fruits are fragile and do not pack or ship well so you won’t find them in stores. This makes them an ideal plant to grow at home!