Herbicides are chemicals that kill weeds. The City uses them carefully and only when other methods aren't enough. The goal is to use as little as possible while still keeping weeds under control. The herbicides the City chooses target weeds specifically, so they don't harm the native grasses and plants that belong there.
Weed management on Open Space
The City of Louisville uses an integrated approach to control invasive and noxious weeds on Open Space. This includes prevention, monitoring, mowing, pulling and, when necessary, targeted herbicide use.
Integrated weed management plan
The City of Louisville uses an Integrated Weed Management Plan (IWMP) to manage weeds on Open Space properties. "Integrated" means they use many tools together, not just one, to get the best results.
Why do invasive weeds matter?
Invasive plants are plants that don't belong in the local area. They spread fast and crowd out plants that are supposed to grow there. This can hurt animals, insects, and the whole ecosystem. Managing these weeds helps protect native plants and keeps open spaces healthy for people, pets, and wildlife.
- List A species are targeted for complete and total removal.
- List B species are managed to prevent further spread.
- List C species are already widespread and are managed through ongoing control and education.
They can spread quickly because:
- They have few natural predators or diseases.
- Wildlife and livestock usually do not eat them.
- They have large root systems that absorb water and nutrients quickly.
- One plant can produce thousands of seeds.
- Some species release chemicals into the soil that make it harder for nearby plants to grow.
When noxious weeds spread, they can:
- Reduce native plant diversity
- Remove food and shelter for wildlife
- Increase soil erosion
- Damage agricultural lands and crops
Managing invasive weeds takes significant time and resources. You can help protect Louisville Open Space by volunteering with programs such as weed whackers and pulling for Louisville.
Herbicide use on Open Space
Chemical control is one tool the City uses to manage invasive and noxious weeds. Herbicides are used when other methods are not effective or practical, with the goal of limiting chemical use while protecting healthy landscapes.
In 2020, the City discontinued the use of glyphosate and 2,4-D on City-maintained Parks and Open Space properties, excluding Coal Creek Golf Course.
This policy applies only to land maintained by the City. It does not apply to private property, City-owned property maintained by others, or jointly owned Open Space.
What you may notice:
- More weeds in some areas: Weeds may be more noticeable along trails, in gravel areas, around landscaping, and in parking lots.
- Some herbicide use: The City may still use other approved herbicides to control invasive and noxious weeds when needed. These treatments do not contain glyphosate or 2,4-D.
How does the city apply herbicides safely?
When the city does use chemicals, they follow strict rules to keep everyone safe:
- Low toxicity: Workers only use the least harmful products available.
- Spot treating: Workers spray only on the weeds, not everywhere, to reduce the amount of herbicide used and lower the chance of it reaching plants or animals it shouldn't.
- Trained workers: Only professionals licensed by the state of Colorado, or someone watched closely by a licensed supervisor, apply herbicides. They follow all state and federal safety rules to keep the community safe.
Look for Yellow Flags: Workers place bright yellow flags at every entrance to a park or trail when they are spraying. These flags warn you to stay away while the chemical is wet. Once the spray is completely dry, the area is safe to use again.
Sign Up for Alerts: You can sign up to get email notices before the city sprays an area.
Pesticide Sensitivity Registry: If you have a doctor's note showing you are highly sensitive to chemicals, you can sign up for the state's official registry. This requires neighbors to tell you before they spray their lawns.
Please note: Being on the Pesticide Sensitivity Registry list means you'll be told about applications on properties right next to yours. It does not cover mosquito spraying or treatments on lawns, trees, or shrubs beyond that boundary.
Helpful links
- Pesticide Sensitive Registry information and application
- Boulder County weed management plan
- Boulder County parks and open space weed division
- Colorado State University Extension office - Boulder County
- Colorado Department of Agriculture noxious weed management program
- Colorado Noxious Weed Act: Title 35 Article 5.5
Additionally, you can help support our weed control efforts through the weed whackers and pulling for Louisville volunteer programs.
Get notified of herbicide applications on Open Space
You can sign up to get email notices before the city sprays herbicides on Open Space properties.