Orange hawkweed (Hieracium aurantiacum) is a relatively new invasive weed in Clackamas County. With your help, our team plans to keep it from becoming a common problem for landowners! A member of the sunflower family, orange hawkweed is native to central and southern Europe and grows in open areas like gravel pits, roadsides, meadows, pastures, […]
Garlic mustard (Alliaria petiolata) is an increasingly invasive weed in our community. Native to central and western Europe, this fast-growing plant commonly invades sites such as parks, trails, roadsides, and streamsides. April is a great time to manage this priority invasive weed on your property. Sometimes referred to as Jack-by-the-hedge, garlic mustard is easily identified […]
It isn’t everyday that a weed manager feels the need to trade in their work boots for a day spent surrounded by home decor and scented candles. Remarkably, such was the case this week for WeedWise program manager Sam Leininger. Early in the week Sam was alerted to the possibility that a national retailer, Pier […]
Since 2016, the WeedWise program has been working to control the largest known infestation of goatsrue (Galega officinalis) in Oregon. Goatsrue is an Oregon class A noxious weed and has been deemed a high priority for control and eradication because it is toxic to livestock and spreads easily. This federal and state noxious weed is only known at a handful of other sites across Oregon and the Pacific Northwest.
Goatsrue flowers
Goatsrue is a deep-rooted perennial, with hollow stems and compound alternate leaves. The compound leaves have a terminal leaflet and 6-10 pairs of leaflets. The tip of each leaflet rapidly narrows to a fine tip. Goatsrue has pea-like flowers that vary in color from purple to white. Flowers bloom from June to October and are clustered at the end of its branches or at the leaf axils. Unlike some other members of the pea family, goatsrue lacks tendrils and grows in a more upright and bushy form rather than as a vine. The seeds are contained in pods with up to 9 mustard-colored, oblong seeds. Each plant can produce 15,000 pods a year. Additionally, these seeds may remain viable for 5-10 years in the soil.
Goatsrue closely resembles some regionally rare native plants, so we encourage landowners to contact us if they think they may have goatsrue on their property.
Robust goatsrue growth
In May of 2016, during one of our planned weed surveys, one of our contracted survey crews discovered a large previously unknown population of goatsrue on two adjacent riparian properties along the Clackamas River. This infestation affects 14 acres and is the largest known infestation of goatsrue in Oregon. At that time, we began a management effort to contain and control this priority weed with the goal of eradication of the goatsrue as well as several other priority invasive plants present at these sites.
This discovery was found as part of extensive surveys of streamside properties along the Clackamas River initiated in 2015 and continuing into the present. Twenty-one priority invasive plant species were on our target list for these surveys. Some of these species had been documented in our region and some had not. These surveys help us to address new priority invasive plants and better manage priority invasive plants established here. We thank private landowners for allowing us to access their properties for these surveys!
Goatsrue herbicide application
The WeedWise Program initiated control soon after detection of this large infestation. Our approach began confirming the identity of the goatsrue. We then followed up with a thorough review of the biology and control of goatsrue. Most notably, we learned that goatsrue can have a long seed dormancy period allowing seeds to grow after 10 years in the soil. As a perennial weed with a deep taproot, it is all difficult to remove by hand. Therefore, our management goals were to prevent all seed production and to target the large root systems of existing plants.
Next, we researched management strategies appropriate for this plant and this site. We also consulted with the Oregon Department of Agriculture Noxious Weed Control Program and the City of Portland Bureau of Environmental Services who both have prior experience managing goatsrue. Based on this research, we selected two herbicides to treat the infestation: one to target upland populations and a second aquatically approved herbicide to treat infestations that occur near water. The herbicide applications were planned by the WeedWise program and implemented using licensed restoration contractors.
What’s Next?To date, our management efforts have been highly successful, but with the size and complexity of the site we did note some patches with regrowth after herbicide application, as well as new seedlings emerging. On follow-up monitoring of the site, we also found several overlooked patches that had grown in an among other vegetation. In response, our current efforts focus on continuing to scout for missed populations and to remove interspersed invasive Himalayan blackberry (Rubus bifrons) stands which may obscure goatsrue plants. We are carrying out multiple rounds of control each year to ensure that we are not letting any plants go to seed and to continue to address regrowth.
After two years of intensive control, we have dramatically reduced the populations and are on track to eradicate this population. Eradication will require ongoing monitoring and control to address the long seed dormancy. Although we won’t be walking away from the site anytime soon, we are optimistic knowing that the population is significantly reduced, and that we are committed to eradicating goatsrue from Clackamas County!
The Scourge of Spurge Laurel Spurge laurel (Daphne laureola) is neither a spurge nor a laurel, but rather an invasive plant in the Daphne family. This perennial plant has poisonous berries, spreads aggressively in our native forests, and is increasingly being found in Clackamas County. Native to Europe, spurge laurel was introduced in Oregon as […]
The Thorn in Our Side Himalayan blackberry (Rubus bifrons) 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 […]
Do you think you’ve found a noxious weed? Here is how you can get help to identify and report your find! One of the most important aspects in controlling invasive weeds is to verify the identification if invasive weeds before you work to control them. Knowing the difference between an aggressive weed and a common […]
September is the Time to Control Japanese Knotweed Japanese knotweed (Fallopia japonica) has been called a “nightmare” and a “botanical bully,” and is one of the 100 worst global invaders. These characterizations give you a pretty good idea of just how unwelcome this invasive weed is in our community. Japanese knotweed is fast growing and […]
Puncturevine (Tribulus terrestris) is aptly named! This invasive weed has spiny seed heads that can easily puncture a bike tire, inflatable raft, animal paw, or footwear. Be on the lookout because it is beginning to make its way into Clackamas County from eastern and southern Oregon. Also known as “goathead”, puncturevine is native to southern […]
Policeman’s helmet (Impatiens glandulifera) is an invasive weed which grows in ditches, wetlands, and along waterways. Native to India, this fast-growing annual was introduced as a ornamental plant due to its impressive growth and the showy purple, pink or white blooms. Since introduction, it has escaped cultivation to become the dominate riparian vegetation in many […]
