Invasive Plant Alerts

Most Recent Alerts | Spreading Invasive Plants | Escaping Garden Plants | Other Alerts

"Alerts" represent either invasive plants that appear to be expanding their range, or species showing signs of being invasive in some areas of the state. It is critical that Cal-IPC members report potentially significant invasions of plants new to an area. Not only does this provide an initial time frame for the invasion, but also alerts land managers in other regions of the state to the potential threat. Rapid action on a new invader can potentially save millions of dollars with preventative control or even eradication. New reports should be made to info@cal-ipc.org.

These Alerts differ from the Alert designation within the Invasive Plant Inventory, which refers to plants with High or Moderate ratings that have the potential to increase their ranges in California. Many of the plants listed below are not included in the Inventory because we do not have enough information to rate them. However, they may be rated in the future.

Most Recent Alerts

2007 Weed Alerts

By Dr. Joe DiTomaso, Weed Science Program, Department of Plant Sciences, UC Davis. View a pdf with photos.

2006 Weed Alerts

By Dr. Joe DiTomaso, Weed Science Program, Department of Plant Sciences, UC Davis. View a pdf with photos.

2005 Weed Alerts

By Dr. Joe DiTomaso, Weed Science Program, Department of Plant Sciences, UC Davis. For more extensive descriptions of these plants, see the 2005 Symposium Proceedings (pdf), p. 88. View a pdf with photos. Photos by Joe DiTomaso unless otherwise noted.

Invasive plants that appear to be spreading (2005):

Piptatherum miliaceum (smilograss) — Widespread perennial bunchgrass in California, mainly on the coast, but also inland. Appears to be expanding its range in southern CA. Produces many viable seeds. Ideal climatic conditions in some years may account for rapid expansion.

Parentucellia viscosa (yellow glandweed) — Widespread throughout the coastal areas of central and northern California, but reports indicate that it is spreading and becoming more of a threat in Humboldt County, and perhaps Del Norte County.

Saccharum ravennae (ravennagrass) — Has been known to escape in southern California, but has recently been rapidly expanding its range along Cache Creek in the Capay Valley between Clear Lake and Woodland. It inhabits disturbed areas near creeks but has also moved into relatively undisturbed riparian areas, occupying much of the same habitat as Arundo donax and Tamarix parviflora.

Centaurea debeauxii (=Centaurea x pratensis) (meadow knapweed) — More invasive in Oregon and Washington, and only sporadically found in northern California, but appears to be rapidly expanding its range in the northwestern corner of the state. Recently listed as an A-rated noxious weed by California Department of Food and Agriculture.

Garden plants that appear to be escaping (2005):

Allium triquestrum (three-corner leek) — Only occasionally escaped outside of urban areas, but is becoming more prevalent along the northern coast, particularly in Humboldt County.

Geranium lucidum (shining geranium) — Recently reported to be invasive in Eugene, OR, by Bureau of Land Management. Found escaping in oak woodlands in mesic/shaded areas, generally under the oaks and in monotypic stands. They tried to hand pull it and it make the problem worse. Probably still only found near the Berkeley Botanical Gardens in CA, but is escaping cultivation there. Keep an eye out for it in wildland areas near there.

Geranium robertianum (herb-robert) — Widespread garden escape in the Bay Area. Just beginning to get established away from urban areas.

Nassella tenuissima (Mexican feathergrass) — Widely sold and grown throughout California. Also called Stipa tenuissima or ponytails. Touted as a good drought resistant plant. Australia and New Zealand list it as a serious threat to agriculture. Q-rated by CDFA in 2004; recently proposed to change to C list. Has not yet established in the wild, but is a frequent escape in gardens. Need to keep an eye on it in wildlands and make sure it does not get established, primarily in coastal areas from the Bay Area to southern California.

Nelumbo lutea (American lotus) — Has taken over much of a 30-acre lake in Tehama County. Need to watch that it does not spread to other areas. Has been invasive in the tropics and the seeds are very long lived, reportedly up to 400 years.

Polygonum aubertii (Chinese fleecevine, silverlace vine) — Perennial vine native to China. Not a widely grown ornamental, but is available. Grows rapidly and forms dense cover; Sunset Western Garden Book says it can grow 100 ft2 per season. Has become established in at least four locations on the banks of San Francisquito Creek in San Mateo and Santa Clara Counties. Appears to move downstream when the stream bank collapses due to high flow conditions. Produces a large number of seeds that also facilitate rapid spread.

Scabiosa atropurpurea (pincushion flower or mourningbride) — Very common cultivar. Began to escape into wildlands 4-5 yrs ago and form near- monotypic stands in San Bruno grasslands. Spreading along trails and fire roads between Claremont Canyon and Strawberry Canyon in Berkeley.

Other Alerts

Cal-IPC Weed Alert! 2004 (pdf) - Presented by Dr. Joe DiTomaso, Weed Science Program, UC-Davis.

2003 Cal-IPC Weed Alert! 2003 New invasions and recent expansions (pdf) - Presented by Dr. Mandy Tu, The Nature Conservancy Wildland Invasive Species Team.

Brachypodium sylvaticum (slender false-brome) - Report sightings of this plant that is spreading in redwood groves of the Santa Cruz Mountains.

The Cal-IPC News occasionally features articles about new invasive plants of concern.

• Knotweeds (Polygonum spp.) article - Spring 2005
• Weeds in northern California article - Spring 2004
• Slender false-brome (Brachypodium sylvaticum) article - Winter 2003/04
• Red sesbania (Sesbania punicea) - Summer 2003
• 2001 Weed Alerts - Fall/Winter 2001
• Invasive mustard article - Fall 1997