Background

In May 2022 the Public Works Department and relevant stakeholders were notified by California Native Plant Society (CNPS) Orange County of a newly identified emergent species in Laguna Beach. Stinking Roger (Osteospermum calendulaceum). This is the first and only recorded observation of this plant occurring in North America, and it has the potential to be a problematic invasive species. The population treated by LCF is approximately 0.7 acres, excluding an additional adjacent population that was treated and surveyed separately by OC Parks. This population is primarily located on the parcel of 650 Laguna Canyon Rd., along the access road to the Laguna Beach Police Department shooting range, east of Poplar Rd. The population also extends across the property boundary shared with OC Parks, along Water Tank Road, and onto Water District property.

Stinking Roger, a member of the Aster family, is a low growing, spreading annual that originates in South Africa and reproduces via dimorphic seed. It appears to grow in dry soil. The flowers of Stinking Roger are small, yellow, and upright. Leaves and stems are glandular and the species has a moderate aroma, which can be described as savory and mildly unpleasant. The leaves are often shallow dentate. Little is known about the potential invasiveness of this species due to lack of observations, but it has been found to be invasive in Southern and Western Australia.

Coordinated Response

Following Ron Vanderhoff’s initial observation, given the lack of understanding regarding the species’ response to the local environment, it was necessary that all stakeholders work together in a coordinated and rapid response. Matthew Barker, City Arborist for the City of Laguna Beach Public Works Department partnered with Laguna Canyon Foundation to perform initial surveys, mapping and staking of the known population. CNPS-Orange County, and the University of CA, Irvine coordinated to analyze seed samples to test germination rates, which will help provide information on the potential invasiveness of the species.   OC Parks staff, LCF, and volunteers provided the initial treatment of Stinking Roger consisted solely of hand-pulling due to the population already having gone to seed. Other coordinated efforts have included stakeholders from Laguna Beach City, UC Cooperative Extension Weed Management, Natural Communities Coalition, Orange County Agriculture Commissioner’s Office, and The California Department of Food and Agriculture. In Sept., 2022 the CA Department of Food and Agriculture gave the species an "A" pest rating, The CA Invasive Plant Council will likely conduct and publish an invasive assessment of the species during 2023 using their PRE modeling tool. 

Challenges

The area where observations occurred are within City Fuel Modification Zone (FMZ) 1, which has been typically goat grazed. The act of bringing goats into this area and then out to other natural areas has been identified as a potential behavior that the plant could exploit in an effort to spread. There is also a large ephemeral streambed and culvert adjacent to the treated population, which could likewise be a potential vector. Also, the mechanism of seed dispersal is not well known at this time. Lastly, the actual population size could be larger than currently recorded. While best efforts were taken to identify additional and/or expanded populations, one area of concern was that much of the surveyed area had been recently mowed by the City’s contracted weed abatement crew, making it difficult to identify plants in these areas. Individual plants that were found and removed, could be part of an unknown larger cluster. Current and future surveys may reveal additional populations as new growth occurs.

Next Steps

A Task Force has been established to distribute information and share resources in order to combat the spread of this plant. The areas identified to be the highest likelihood of hosting a colony have been determined, and surveys are ongoing to see if these areas become vectors. Diligent monitoring, documentation, coordination, and execution of the plans will yield results. After observations of this plant’s physiology for a full year, we now know can accurately time treatments with this plant’s physiology. Pre-emergent treatments are be applied before the seeds in the ground germinate, and foliar applications and hand pulling will be used for plants that sprout, before they are able to reach their fruiting period.

Additional Information and Contact If you have any questions, please reach out to Matthew Barker, City Arborist for the City of Laguna Beach at (949) 464-6674 or send an email to mbarker@lagunabeachcity.net.

Please visit the California Native Plant Society’s Taxon Report for this species. If you would like more information on invasive plants, in general, please visit the California Invasive Plant Council’s (CAL-IPC) website.