volunteers pulling and bagging stinkwort

Stopping the Stinkwort Invasion

Despite its dainty foliage, stinkwort (Dittrichia graveolens) spells big trouble on the American River Parkway.

Native to southern Europe, stinkwort was first observed in the Sacramento region in 2002, thought to have been introduced by seeds in landfill soil. This spunky plant thrives in hot, dry weather and soils that are gravelly, saline, or even contaminated with heavy metal. The fast-growing annual can be found in grasslands, but also performs well in areas where the ground is disturbed or nearly bare, such as fire breaks and along the edges of highways, roads, and trails.

Stinkwort gets its name from the camphor-like smell of its sticky, resinous foliage. The annual plant germinates in the winter, remaining small until spring when it grows rapidly into a three-foot tall, upright shrub.

Invading Spaces

stinkwort weed growing along roadway, person pulling plant

removing stinkwort along a roadway

An invasive plant like stinkwort can dominate an ecosystem by out-competing native food plants. Being non-native, it provides no benefit to Parkway animals and insects and lacks natural limitations on its growth. It crowds out native plant species by overtaking resources, such as sunlight, nutrients, and water, disrupting an already fragile habitat.

Stinkwort also contains  phytotoxins that inhibit the growth of surrounding vegetation, giving it a greater advantage over other plants.

Parkway wildlife species are dependent upon native plants for food and shelters, and some plant-eaters create important food sources for other species. For instance, insects that feed on a specific native plant may be an essential protein source for frogs, lizards, and birds. The decline of the native plant harms the insects, and the decline of the insects then harms the other animals, rippling throughout the food chain.

 

 

A Seedy Battle

stinkwort seeds

stinkwort seeds, photo credit: Country Mouse

A member of the sunflower family, stinkwort blooms in September, when other plants are already dormant or have gone to seed. Its small, yellow flowers produce highly transportable, dandelion-like seeds that are easily moved by water and wind. They also travel by gripping a variety of surfaces, including animal fur, human clothing, and vehicle or bicycle tires.

According to USDA reports, a single stinkwort plant can produce an estimated 70,000 tiny, highly transportable seeds known to move over 200 meters in the air — about two football-field lengths. This means that removal efforts must be diligently repeated until the bank of fallen seeds around the original plant has been depleted, and surrounding land must be regularly monitored for new areas of growth.

Fortunately, stinkwort seeds have a short life in soil, remaining viable for only two to three years.

 

Easy to Pull, Difficult to Contain

removing stinkwort with hand trowel

removing stinkwort with hand trowel

Stinkwort is known to defy most control methods, even returning rapidly after wildfire. Hand-pulling has proven to be the most reliable way to remove the weed. It has a relatively short root system, making it easy to pull out, especially after a rain.

However, if part of the plant remains, it can quickly regrow. Yet another challenge is that stinkwort seeds can ripen on pulled or cut plants if they have already flowered. Extracted plants must be securely bagged if they have any flowers or buds to avoid spreading seeds.

 

 

 

 

 

 

Tricky to Identify

stinkwort with small yellow flower

stinkwort with flower buds

Removing stinkwort from the Parkway habitat begins with accurately identifying the plants, which isn’t as simple as it may sound. Our Invasive Plant Management Program (IPMP) volunteers are trained to distinguish this invasive plant from important native plants that look incredibly similar.

 

 

 

 

tarweed yellow flowers

tarweed flowers, photo credit: The Amateur Anthecologist

One such beneficial plant is tarweed (Madia elegans). Like stinkwort, tarweed is also an annual shrub with sticky, aromatic foliage, small yellow flowers, and tiny seeds that easily parachute. It is also a late-bloomer and thrives in full sun, low water conditions, and the unwelcoming, hard-packed soil along roadsides.

Unlike stinkwort, tarweed is a native plant. The seeds of tarweed are eaten by many birds and small mammals, such as mourning doves, quail, mice, and ground squirrels. Blooming through the fall, tarweed is an important late-season nectar source for butterflies and pollen source for bees.

 

 

 

 

Dangerous Encounters

pulled stinkwort plant

pulled stinkwort plant

The hazards of stinkwort warrant special handling by volunteers and extend beyond the Parkway ecosystem. The plants also are known to cause allergic reactions and severe dermatitis in some people who come in contact with the sticky resin, so we provide our volunteers with protective gloves to wear while pulling and bagging the weeds.

Dogs that walk through dense patches of stinkwort have been known to vomit, reportedly from ingesting or inhaling the bristles, according to some studies.

Oils in the plant have been known to taint the flavor of meat and milk of animals that have consumed the plants. Sadly, stinkwort seeds can kill grazing livestock, such as sheep and horses. Barbs on the fluffy-tipped seeds reportedly damage the animals’ digestive systems. 

 

 

 

 

Join the Effort

Because stinkwort is relatively new to the region, we may still have time to effectively eradicate it from the Parkway with vigilant efforts.

Invasive plant management is an essential part of conserving and nurturing the American River Parkway. Stinkwort is one of several invasive plant varieties that compromise the Parkway ecosystem and are managed by ARPF and our team of trained volunteers.

You can get involved by signing up for volunteer training or by making a donation to our Invasive Plant Management Program.

close up of yellow Spanish Broom flowers, blue sky in background

Putting the Squeeze on Spanish Broom

Spanish broom (Spartium juniceum) is a beautiful, hearty shrub with elegant yellow flowers.  It is a fast-growing  variety of the pea family, growing up to 10-15 feet tall in just a few years with roots that can extend several feet below the surface, even through rocky soil conditions.

It was introduced to California in 1848 as durable landscape ornamental because of its draught-tolerant properties and ability to root in less than ideal soil. By the late 1930s, Spanish broom was planted along mountain highways to prevent erosion.

So, why the fuss over such a pretty, practical plant?

Originating in the southern Mediterranean region of Europe, Spanish broom is an invasive, non-native plant that has no natural local predators and provides no benefit to native insects and animals. With nothing to keep it in check, Spanish broom quickly overtakes resources — sunlight, nutrients, and water — needed by native plants, which are needed  by area wildlife.

Because it can grow in tall, dense patches and produce substantial dry matter, Spanish broom can also create a serious fire hazard during the dry season.

How is Spanish broom removed?

Removing Spanish broom isn’t easy, and must include pulling out the entire root system to deter it growing back stronger. It also involves specific training and diligent repetition.

Even if the whole plant and root system are removed, seeds are a factor. One plant can produce 7,000 to 10,000 seeds in one season, and the seeds can remain viable for decades. A large seed bank is likely present in the soil around any mature Spanish broom plant. Seeds can also be moved to new locations by erosion, rain wash, and possibly ants.

Parkway areas where Spanish broom has been removed in the past are likely to have new plants sprout for years to come, and the plant can also establish itself in new locations. Restoring the natural habitat is a slow process that requires regular monitoring and proper removal of Spanish broom on an ongoing basis.

Identification
Spanish broom twig with orange ribbon tag

Spanish broom plant identified and tagged.

The first step with Spanish broom removal is accurately identifying the plants. When in bloom, the plants are more visible with their bright yellow flowers. However, after the plants have dropped their leaves, this becomes more difficult. Trained volunteers may need to scout and tag the shrubs for later removal during an Invasive Plant Management Program (IPMP) group event.

 

 

 

 

 

 

 

 

 

 

 

Equipment
two orange weed wrench tools

Weed wrench tools.

Because the root system is strong and must be removed completely, Spanish broom extraction requires special equipment, including a weed wrench designed to grip the base of the plant and gradually employ leverage to lift it out. This industrial tool costs about $250 each.

Other useful tools are trowels and pickaxes to help loosen surrounding soil and dislodge rocks.

 

 

 

 

 

 

 

 

Extraction Process
pulled Spanish broom root

Spanish broom root system.

Ideally, the weed wrench removes the whole plant, roots and all. Extraction tends to be more difficult during a draught season and easier after a good rain. According to long-term ARPF IPMP volunteer Dennis Eckhart, an established Spanish broom plant in challenging conditions can take as long as 30 minutes to remove properly.

 

 

 

 

 

 

 

 

 

 

 

weed wrench close up with plant

Weed wrench in action.

In reality, this process is not only labor-intensive, it requires finesse to avoid breaking or shredding the plant stem. When seed pods are present, they must be collected before extracting the plant.

 

 

 

 

 

 

 

 

 

 

broken Spanish broom stem

Broken Spanish broom stem

If the plant stem does break, creative problem-solving is important. Broken root systems can grow back even stronger than before, making it more difficult to remove them next year. Volunteers must dig down around the root, remove rocks, twigs, and vines, and attempt new approach angles — all while trying to minimize disruption to the surrounding natural habitat.

 

 

 

 

 

 

 

 

Invasive plant management is an essential part of conserving and nurturing the American River Parkway. Spanish broom is one of several invasive plant varieties that compromise the Parkway ecosystem and are managed by the American River Parkway Foundation and our team of trained volunteers.

You can get involved by signing up for volunteer training or making a donation to our Invasive Plant Management Program.