The City of Louisville uses an Integrated Weed Management Plan (IWMP)  to control weeds on City-maintained Open Space. Weed control efforts employ a combination of prevention, monitoring, education, cultural control, mechanical control, biological control, and chemical control methods.

Chemical control involves the use of herbicides to eradicate weeds. By using an integrative weed management program, weed control is more effective and chemical applications are minimized. Selective synthetic herbicides are used in the City’s Open Spaces to:

• Eradicate or stop the spread of noxious weed species regulated by the Colorado Department of Agriculture under the authority of the Colorado Noxious Weed Act.
• Control other non-native weeds that are detrimental to native flora and fauna.

Herbicides used are selective and target weed species while leaving desirable native and pasture grasses unharmed.

The herbicides glyphosate and 2,4-D are no longer used on City-maintained Open Space

In 2020, the City of Louisville discontinued the use of glyphosate and 2,4-D in City-maintained parks and Open Space, excluding Coal Creek Golf Course.

Glyphosate and 2,4-D are synthetic herbicides used to control a variety of weeds. The City made the decision to discontinue using these two herbicides in response to public concerns regarding the use of these chemicals in areas that children, adults, pets, and wildlife frequent. This decision does not apply to privately owned property, City properties that are privately maintained, or jointly owned open space lands.

You can expect the following:

• You will see more weeds.
  More weeds may be noticeable in rock beds, shrub beds, parking areas, and trails as our new approach will be less effective than the chemical applications previously used in these areas.
• You will still see spraying.
  Chemical control will continue to be used as a weed management tool on City-maintained Open Space, but will no longer include the use of or containing glyphosate or 2,4-D.

Herbicide Application

• When herbicides are used, the lowest toxicity herbicides are chosen from a list of products that have been reviewed and evaluated by qualified staff. Treatment areas are mostly spot-treated (as opposed to broadcast-treated) to reduce amount of herbicides used and decrease potential for non-target exposure and off-site movement.
• Applicators employed or contracted by the City are either licensed or monitored by Qualified Supervisors licensed by the Colorado Department of Agriculture as pesticide applicators.
• Chemicals are applied following the City’s newly updated policies and all applicable state and federal guidelines.
• For questions or more information regarding herbicide applications on Open Space, contact Catherine Jepson at 303-335-4742 or CatherineJ@LouisvilleCO.gov

How to avoid contact with herbicides

• Sign Up for e-notifications >
  The link to the e-notification is currently down. Please see upcoming treatment locations and dates listed below:

Weather permitting, herbicide applications will occur at the following Open Space properties on Tuesday, October 8 through Thursday, October 10:

• Bullhead Gulch
• Coyote Run
• CTC
• Dutch Creek
• Hillside
• Warembourg

Yellow warning flags will be posted at all property entrances when applications are in progress. 

All applications are done in compliance with state and federal guidelines as well as the City’s Integrated Weed Management Plan and City Council direction to discontinue the use of glyphosate and 2,4D. For general weed control information for the Department of Parks, Recreation, and Open Space, please see our Integrated Weed Management Plan. For questions regarding the specific weed control applications listed above, please contact Catherine Jepson at catherinej@louisvilleco.gov  

• Yellow flags are posted at all entrances to areas where herbicides are being applied. Flagging during application is a requirement of the Colorado Department of Agriculture. It serves to inform the public and help eliminate public contact with the herbicide when it is wet. All herbicides used by the City are considered safe once dry.
• Sign up for the Colorado Pesticide Sensitivity Registry >
  This registry is maintained by the Colorado Department of Agriculture for people who have documentation of sensitivity to pesticide products. Residents on the registry are required to be informed of applications occurring on adjacent abutting properties only. It does not pertain to mosquito spraying or any pesticide applications other than those made to control pests of lawns, trees and shrubs.

For questions or more information regarding herbicide applications at specific properties:

• Open Space: contact Catherine Jepson at 303-335-4742 or CatherineJ@LouisvilleCO.gov
• Golf: contact David Dean at 303-335-4735 or DavidD@LouisvilleCO.gov
• Parks: contact Erik Swiatek at 303-335-4777 or ErikS@LouisvilleCO.gov