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  • Megan Kaun

Caltrans' Chemical Vegetation Management Contributes to Road Hazards

Sinkholes and mudslides linked to roadside pesticide use


This has been a water year to remember in California. We have been hit with countless atmospheric rivers and extreme weather events. Much of the state has received over 200% of average precipitation. With climate change predictions pointing at this being a "new normal", we are being invited to rethink how we treat our land to better manage large amounts of water flow from both rain and snow melt.


Caltrans' current vegetation management strategies that rely heavily on pesticides is further exacerbating many of the flooding and road issues we have lived through this year. Reliance on chemicals to kill plants along roads leaves bare dirt with nothing to hold it in place. Even during normal rain events, this released sediment causes problems in rivers, ecosystems, and on roads. During large rain events like the ones we've seen this year, this roadside erosion can be catastrophic.

Sinkhole in Napa, California, winter 2023.


Eroded sediment clogs culverts that are needed to manage the flow of water around paved surfaces. When culverts are clogged from too much sediment, the flowing water often takes a path that eventually compromises the structural integrity of the road. This can lead to dangerous sinkholes and mudslides.


Culverts clogged with eroded sediment.


Along the Pacific Coast Highway (California Highway 1) in Malibu, Caltrans manages roadside vegetation with heavy pesticide spraying. Mudslides were reported up and down the Pacific Coastal Highway this year.

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Soil erosion below the pesticide "spray line" where no plants can grow. Photo taken along the Pacific Coast Highway in Malibu, CA, 2023.


This year in Minnesota, the state government approved House File 498 "Highways for Habitat" that requires the Minnesota DOT to create habitat in highway right of way areas as part of their Integrated Roadside Vegetation Management program. Minnesota DOT testified that they are committed to planting 75% of roadsides in native plants. Road maintenance engineers noted that heavy pesticide use leads to expensive road repairs when bare dirt erodes and leads to sinkholes.


Taking a fresh look at how we manage roads could be a key part our response to climate change, and an important step toward resiliency.

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