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Invasive Weed Eradication Program

Carlsbad City Council approved on Tuesday a program to eradicate a highly invasive plant, Ward’s weed. Ward’s Weed is a threat to native habitats, protected plant and animal species, and recreational and agricultural areas in Carlsbad.

Ward’s weed was first discovered in Carlsbad in 2008, which was the first discovery in North America, and is now known to have spread to approximately 200 acres of habitat within the city’s Habitat Management Plan preserves. See a map of the areas of infestation.

Invasive, non-native species are one of the greatest threats to the city’s preserve system. It is not known how Ward’s weed got into the area.

Ward’s weed can grow as a thick mat that chokes out all other native plant species. Rosanne Humphrey, the city’s senior environmental program manager, says “due to the extremely high seed count of up to 30,000 seeds per plant per year, this species can spread quickly, and presents a fire hazard in our open spaces and canyons. It is considered a flashy fuel which means that it could ignite easily and burn quickly.”

Protecting the city’s open space and the natural environment is one of the core values identified in Carlsbad’s Community Vision and the city has a legal obligation to protect a 6,478-acre native habitat preserve system. Control of non-native plants is an essential component of this effort.

Investing in early and aggressive control of the species will save the city a significant amount of resources in the future. The City Council approved up to $200,000 in funding to add to the $200,000 in grant funding obtained by the Nature Collective, San Diego County and Center for Natural Lands Management for a total of $400,000 over the two-year program. The sources of grant funds include SANDAG and California Wildlife Conservation Board.

The aggressive treatment strategy consists of spraying a pre-emergent herbicide that suppresses seed germination, approximately one or two weeks before measurable rain arrives in November or December. This does not harm most woody shrubs, grasses or bulb species.

Organic herbicides are not effective on Ward’s weed because only the above ground portion of the plant are killed, so the plants continue to re-sprout from live roots.

The city’s current Integrated Pest Management Plan allows the use of herbicide “if deemed necessary by supervisory staff to protect public safety; to prevent threat to sensitive species or habitats; to assist in meeting regulatory compliance requirements; or to prevent economic loss-when pests cannot be managed by other tactics.”

“We have an opportunity to potentially eradicate a new invasive species that could spread throughout southern California and beyond, said Humphrey. “If Ward’s weed is not eradicated early, the cost of invasive species treatment and the damage done to native habitats will be significantly greater into the future. “

Ward’s weed can look like anything from a single, short stem to a dense, compact shrub similar to tumbleweed. Because it is an annual plant, Ward’s weed is green in the winter, and dries up and dies in the summer. The easiest way to identify this plant is by the small, round seed pods that are found all along the stems. 

If anyone thinks they have spotted Ward’s weed, please take some close-up photos and email to Rosanne.humphrey@carlsbadca.gov with a detailed description of the location. 

October 9, 2019