Yolo County Weed Management Area

Barbed goat grass
05
Mar

Yolo County Weed Management Area

The mission of the Yolo County Weed Management Area (YCWMA) is to promote and coordinate efforts toward the management and control of the county’s noxious weeds through education and cooperation with landowners, agencies, organizations and the general public.

Target Weeds (as of 2020)

If you’ve seen any of the weeds below, please let us know! You can either create an account (or use your existing account) on CalFlora and join our group  (Yolo County WMA) to add your noxious weed observations yourself or reach out to our project manager Tanya Meyer at meyer@yolorcd.org. 

1. Regionally rare weeds

 These plants are known to be highly invasive but are still only found in small populations here.  They are a prime target for early detection rapid response (EDRR).  If you find any of these plants, please inform the YCRCD.

Acroptilon repens  

Russian knapweed is a perennial plant with a purple flower and lanceolate leaves that likes to grow in disturbed (usually moist) areas such as farm edges or stream banks. It can spread through it’s robust root system, which makes it a strong competitor that is capable of pushing out other plants to form dense patches.  

 CDFA rating: B 

Cal-IPC rating: Moderate

 

More Resources:

Cal-IPC Page

Weed Research and Information Center Pdf

Cal Flora 

Alternanthera philoxeroides

Alligatorweed is an aquatic perennial plant  that forms dense floating mats but usually grows in shallow water. Because of the dense mats it forms, it can block out light from native vegetation, cause flooding, and create habitat for mosquitos and diseases. 

CDFA rating: A

Cal-IPC rating: High

 

 

More Resources:

Cal-IPC Page

Weed Research and Information Center Pdf

Cal Flora 

Carthamus lanatus

Woolly distaff thistle is an annual plant that grows primarily in the winter on rangelands and disturbed open spaces like roadsides and grain fields. It can be identified by its yellow flower and a spiny leaves. It is a threat because of its ability to compete against native rangeland species and cause harm grazing livestock.  

CDFA rating: B

Cal-IPC rating: High

 

More Resources:

Cal-IPC Page

Weed Research and Information Center Pdf

Cal Flora 

Centaurea calcitrapa

Purple star thistle can be both an annual or perennial with a purple flower and spiny head. It can create thousands of seeds and a large taproot which helps it outcompete natives on rangelands, open forests, and riparian areas. 

CDFA rating: B

 Cal-IPC rating: Moderate

More Resources:

Cal-IPC Page

Weed Research and Information Center Pdf

Cal Flora 

Centaurea iberica

Iberian thistle is very similar to Purple star thistle with a purple flower and spiny head with the main difference being that it prefers moist areas like banks and watercourses (instead of rangelands). 

CDFA rating: A

Cal-IPC rating: not listed

More Resources:

Weed Research and Information Center Pdf

Cal Flora 

Chondrilla juncea

Skeletonweed gets its name from it’s characteristic wiry, branched stems. This biennial to perennial weed forms a deep taproot that helps it compete for water and nutrients. It prefers disturbed soils on roadsides, farm edges, and rangelands. 

CDFA rating: A

Cal-IPC rating: Moderate

More Resources:

Cal-IPC Page

Weed Research and Information Center Pdf

Cal Flora 

Euphorbia oblongata

Oblong spurge is a perennial weed with elliptical leaves and a yellow flower. It likes to inhabit disturbed sites, forming dense patches that exclude any desirable vegetation. This plant can survive many climates, able to withstand anything from flooding to freezing to hot dry summers. 

CDFA rating: B

Cal-IPC rating: Limited

More Resources:

Cal-IPC Page

Weed Research and Information Center Pdf

Cal Flora 

Iris pseudacorus

The yellow flag iris was originally introduced as a pond ornamental because of it’s beautiful yellow flower. Unfortunately, in natural settings, this iris forms dense stands around bodies of water, crowding out native vegetation and reducing habitat for waterfowl and fish, and is also toxic to animals when ingested. 

CDFA rating: B

Cal-IPC rating: Limited 

More Resources:

Cal-IPC Page

Weed Research and Information Center Pdf

Cal Flora 

Lepidium draba

Whitetop (sometimes called Hoary cress) is a perennial weed with a big white flowerhead that can reproduce both by seed and root shoots. This weed can grow in many soil types under many conditions, preferring disturbed sites, and can completely displace native vegetation. 

CDFA rating: B

Cal-IPC rating: Moderate

More Resources:

Cal-IPC Page

Weed Research and Information Center Pdf

Cal Flora 

Sesbania punicea

Red sesbania is a deciduous shrub or small tree with red flowers and drooping pinnately compound leaves. It is a concern because it usually grows in moist areas adjacent to waterways, forming impenetrable patches, and produces seed that are toxic to animals.

CDFA rating: B

 Cal-IPC rating: High

More Resources:

Cal-IPC Page

Weed Research and Information Center Pdf

Cal Flora 

Solanum elaeagnifolium

Silverleaf nightshade or Silverleaf horsenettle is a small perennial herb with silver leaves and purple flowers. It is toxic, like most plants in the nightshade family. It tends to occur in disturbed or overgrazed areas and is generally avoided by livestock and wildlife. 

CDFA rating: B

Cal-IPC rating: not listed

More Resources:

USDA Plant Guide pdf

Cal Flora 

2. Established weeds (with outlier populations)

These plants are already established in our county, but they are often found in small patches.  These “outlier” populations should be controlled before they take over the site.

Alianthus altissima

Tree of heaven is a fast growing tree/shrub that escaped from cultivation as an ornamental and has become well established in many areas of California. It has grey bark, long pinnately compound leaves, yellow flowers, and clusters of winged seeds.   

CDFA rating: C

Cal-IPC rating: Moderate

More Resources:

Cal-IPC Page

Weed Research and Information Center Pdf

Cal Flora 

Aegilops triuncialis

Barbed goat grass is an annual grass most easily identified by its large rigid seed heads with three spikey awns, reminiscent of a goat head, which make it unpalatable and dangerous for livestock and wildlife. This grass sprouts early and aggressively, allowing it to dominate rangelands and disturbed ground. 

CDFA rating: B

Cal-IPC rating: High

More Resources:

Cal-IPC Page

Weed Research and Information Center Pdf

Cal Flora 

Dittrichia graveolens

Stinkwort is an annual flowering plant with sticky bright green foliage, small yellow flowers, and a distinctive smell. It grows primarily in disturbed sites on the urban fringe, but is beginning to invade open riparian and grazing areas. 

CDFA rating: B

Cal-IPC rating: Moderate

More Resources:

Cal-IPC Page

Weed Research and Information Center Pdf

Cal Flora 

Lythrum salicaria

Purple loosestrife is a perennial aquatic weed with magenta flowers that is an extremely aggressive colonizer in any area with seasonally or annually available water, from marches to lake shores. It can take over an area in a single season and is not very palatable, so it poses a great risk to wildlife habitat.

CDFA rating: B

Cal-IPC rating: High

More Resources:

Cal-IPC Page

Weed Research and Information Center Pdf

Cal Flora 

Phytolacca americana

American pokeberry is a tropical ornamental shrub that has escaped to inhabit woodlands, rangelands, and disturbed sites like roadsides and farm edges. It has dark purple berries, large egg shaped leaves, and a distinctive red stem that make it easy to identify. This plant is toxic to all mammals, so it is a threat to native wildlife populations. 

CDFA rating: not listed

Cal-IPC rating: Limited

More Resources:

Cal-IPC Page

Weed Research and Information Center Pdf

Cal Flora 

Saccharum ravennae

Ravenna grass is one of the largest grasses in the state with large feathery seed heads on stalks that can get up to 6 feet tall. It so far is only widespread along the edges of Cache Creek here in Yolo County, but there is concern it could escape to other watersheds. 

CDFA rating: not listed

Cal-IPC rating: Moderate

More Resources:

Cal-IPC Page

Cal Flora 

 3. Other Weeds 

As you may have noticed, there are some common wildland weeds that did not make it into the list of target weeds. Those are the weeds are so firmly established in Yolo County that the WMA does not have the resources to actively manage them under normal circumstances. 

Arundo donax

Arundo (or Giant reed) is a very large perennial cane (like bamboo) that grows extremely fast, about 4 inches a day, using a lot of water and taking up a lot of space along waterways. It also can reproduce by seed and vegetatively, so it can spread quickly through watersheds and already covers a lot of Yolo County’s sloughs and creeks. 

The Yolo RCD is currently working on a largescale Arundo Eradication project. Click here to learn more.

More Resources:

Cal-IPC page

Weed Research and Information Center pdf

Cal Flora page

Rubus armeniacus

The Himalayan blackberry is believed to have originated in Armenia, brought over for its large and sweet fruit. It can occupy any land close to water, creating huge brambles that effectively outcompete any other vegetation, including our native blackberry. While the Himalayan blackberry does provide some habitat function, it’s aggressive behavior still makes it a threat to native ecosystems. 

More Resources:

Cal-IPC page

Weed Research and Information Center pdf

Cal Flora page

Elymus caput-medusae

Medusa head is an annual grass that forms monotypic stands, threatening rangeland diversity and reducing grazing capacity. It gets its name from its long awns and awn-like glumes that persist even after the seeds have fallen off. Medusahead has a lot of lignin in its stems and leaves that degrades slowly and is hard for herbivores to digest, so it has very low forage value and also can increase fire risk. 

More Resources:

Cal-IPC page

Weed Research and Information Center pdf

Cal Flora page

Lepidium latifolium

Perennial pepperweed is common wherever there the water table is high, especially disturbed areas, and can form dense monocultures. It’s robust root system makes it very hard to kill, and often mechanical removal can increase it’s numbers.  

More Resources:

Cal-IPC page

Weed Research and Information Center pdf

Cal Flora page

Conium maculatum

Poison hemlock is an invasive from Europe that likes to inhabit moist soils along streambanks, hedgerows, woodlands, and meadows. As it’s name suggests, all parts of the plant can be poisonous to most mammals, making it a dangerous plant to have around. It can be identified by its tripinnately compound leaves (like carrots), tall mature form, and white  

More Resources:

Cal-IPC page

Weed Research and Information Center pdf

Cal Flora page

Centaurea solstitalis

Yellow star thistle is one of the most notorious weeds in the West, able to create large monotypic stands in are hard to control. The spiny yellow flowers make it unpalatable for most herbivores, even causing chewing disease in horses. 

More Resources:

Cal-IPC page

Weed Research and Information Center pdf

Cal Flora page

Tamarix parviflora

Tamarisk is a small tree or shrub with tiny scale-like leaves that usually grows beside rivers and lakes but is tolerant to many different climates and soils. It provides very little habitat value for native wildlife and, in large numbers, can seriously reduce water tables. 

More Resources:

Cal-IPC page

Weed Research and Information Center pdf

Cal Flora page

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