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.
The YCWMA promotes and coordinates efforts toward the management and control of the County’s noxious weeds through education and cooperation with landowners, agencies, organizations, and the general public. The group is led by the Yolo County Department of Agriculture and the Yolo County Resource Conservation District (Yolo RCD).
The YCWMA was formed in 1999 through a coordinated effort between federal, state, county, and local agencies, private industry, and landowners that were jointly concerned about the explosion of invasive plant species in Yolo County. The YCWMA has a strategic plan and a Memorandum of Understanding (MOU).
The YCWMA has carried out a number of successful projects, including: reducing perennial pepperweed and yellow star thistle infestations at Grasslands Regional Park to protect special status species, controlling small populations of CDFA rated noxious weeds, and establishing native grass along roadsides to prevent re-invasion. The Yolo RCD has most recently been involved with coordinating the outreach effort, including mapping known weed populations and hosting informational meetings, as well as some of the on the ground control of the target weeds.
What is a noxious weed?
A ‘noxious weed’ is any species of plant that is, or is liable to be, troublesome, aggressive, intrusive, detrimental, or destructive to agriculture, silviculture, or important native species, and difficult to control or eradicate (definition as per the California Food and Agricultural Code). A common characteristic of all noxious weeds is their aggressive, competitive behavior. Typically, they steal precious moisture, nutrients, and sunlight from surrounding plants thus, impacting native vegetation.
Why is the management of ‘noxious weeds’ important?
California is a state prized for its beauty and biodiversity with high numbers of native (and even endemic) plant and animal species. In these open spaces, non-native invasive weeds have the ability to disrupt natural ecosystem process. This disruption can affect wildlife by reducing the available food and shelter, damage waterways by increasing erosion, and degrade recreational opportunities by blocking trails and stream banks. Weeds are already here in Yolo County, so it’s important that we do everything we can to reduce the impact of existing weed populations and prevent any new weeds from establishing.
Because each weed species behaves differently in the environment, groups like the California Invasive Plant Council and California Department of Food and Agriculture have come up with specific ratings systems to help describe them. These ratings are often based on the threat posed to ecosystems and the current population size of each weed.
California Department of Food and Agriculture (CDFA) Ratings
Taken from: https://www.cdfa.ca.gov/plant/IPC/encycloweedia/winfo_weedratings.html
A – “A pest of known economic or environmental detriment and is either not known to be established in California or it is present in a limited distribution that allows for the possibility of eradication or successful containment […].
B – “A pest of known economic or environmental detriment and, if present in California, it is of limited distribution […].
C – “A pest of known economic or environmental detriment and, if present in California, it is usually widespread […].”
Q – “An organism or disorder suspected to be of economic or environmental detriment, but whose status is uncertain because of incomplete identification or inadequate information.”
D – “An organism known to be of little or no economic or environmental detriment, to have an extremely low likelihood of weediness, or is known to be a parasite or predator. There is no state enforced action.”
W – “This notation indicates that a plant is included in the CCR Section 4500 list of California State Noxious Weeds.”
California Invasive Plant Council (Cal-IPC) ratings
Taken from: https://www.cal-ipc.org/plants/inventory/
High – These species have severe ecological impacts on physical processes, plant and animal communities, and vegetation structure. Their reproductive biology and other attributes are conducive to moderate to high rates of dispersal and establishment. Most are widely distributed ecologically.
Moderate – These species have substantial and apparent-but generally not severe-ecological impacts on physical processes, plant and animal communities, and vegetation structure. Their reproductive biology and other attributes are conducive to moderate to high rates of dispersal, though establishment is generally dependent upon ecological disturbance. Ecological amplitude and distribution may range from limited to widespread.
Limited – These species are invasive but their ecological impacts are minor on a statewide level or there was not enough information to justify a higher score. Their reproductive biology and other attributes result in low to moderate rates of invasiveness. Ecological amplitude and distribution are generally limited, but these species may be locally persistent and problematic.
Alert – An Alert is listed on species with High or Moderate impacts that have limited distribution in California, but may have the potential to spread much further.
Watch – These species have been assessed as posing a high risk of becoming invasive in the future in California.
The transportation of contaminated hay, seeds, flower arrangements, nursery stock, and other apparently harmless purchases have introduced many noxious weeds to California. Some so-called noxious weeds are escaped ornamental plants that have gone wild, like Tree of Heaven, fertile Baby’s Breath, or Purple Loosestrife. Most people are unaware that bringing even one plant or seed packet across state borders can create a new plant infestation. This can disrupt native vegetation.
Prevention and early detection allow us to eradicate new outbreaks and devote our principal efforts toward management and containment of existing, large-scale infestations.
Prevention tips
- Always check your vehicle for plants or seeds when leaving an infested site.
- Be aware when moving dirt, compost, or equipment since seed can be viable for up to 10 years.
- Do not be tempted by attractive flowers from other states or counties. Do not introduce its seeds or seedling into the state or county.
- Report known locations and sightings by adding observations to the YCWMA group page on CalFlora (will require you to make an account).
- Tell neighbors and friends about noxious weeds.
- Join the Yolo County Weed Management Area by reaching out to Tanya Meyer at meyer@yolorcd.org or visiting our page at Cal-IPC.
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
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
