Herbicide Application – Russian knapweed (Rhaponticum repens)

Partial Preserve Closure: May 26, 7am-5pm

Reopens Monday, May 26 at 5pm

Invasive plant management is an essential pillar of restoration. Without the removal of noxious weeds, creating space for diverse flora and fauna is impossible. There are many methods of managing invasive plants, all of which OVLC has utilized according to the nuances of each plant and the condition of the site.

Russian knapweed (Rhaponticum repens) is a noxious plant that has established itself at the Ojai Meadows Preserve over the past couple of decades. According to the California Invasive Plant Council, it is poisonous to most animals and has allelopathic properties. This means that it prevents all other plants from growing around it. It does this by pulling toxins from the soil and concentrating these toxins at the surface surrounding it. The plant spreads through its rhizomes, creeping roots that grow in a complex matrix under the soil. These extensive roots are able to tap into deep pockets of groundwater—and as the population takes over an area, it creates its own cone of depression, sucking groundwater from far below the root systems of our native species. This story is well-documented throughout the western United States, as fields of this competitive plant have dominated acres, making them inhabitable to plants and animals.

OVLC has worked tirelessly to control the spread of this population, using a wide range of control methods over the years. We have physically removed the population every year to no avail. Despite constant battles of hand pulling, weed whacking, and sheet mulching, the Russian knapweed has continued to spread, encroaching on our restoration sites and invading the native plant nursery. After evaluating our efforts to control this noxious plant, we determined that we are barely making a dent in the population. As such, we have consulted with qualified biologists and determined the most effective treatment is to conduct a targeted treatment with herbicide. This treatment will take place at the Ojai Meadows Preserve on Monday, May 26, 2025.

It is important to note that herbicide use in restoration is a target specific tool, not a blanket application. The herbicide will be applied in globs. This decision was made with careful consideration after exhausting all other options and fully understanding the weight and effectiveness of this approach. Furthermore, the treatment has been scheduled during summer when school is not in session, and a licensed applicator and trained crew will be on scene to minimize adverse impacts and effectively control the noxious knapweed. 

For the safety of preserve users, Lomita Ave. and Besant Rd. entrances will be closed for the day from 7am-5pm. You can still access the eastern side of the preserve from the Maricopa Highway entrances.

This is  the third annual herbicidce treament of the knapweed. We will continue monitoring the population for three years to assess the effectiveness to determine if additional re-treatments are necessary. Once the population is eradicated from the area, we will plant a diverse array of native plants that will restore the soil structure, increase water infiltration, provide seeds for nursery propagation, and provide habitat for hundreds of living beings. 

Have questions or concerns? Contact us at communications @ovlc.org / (805) 649-6852