Weed eradication for 35 acres

Asked August 14, 2017, 11:31 AM EDT

Good morning, we have a 35 acre parcel in Larimer county that needs some weed work for musk thistle, and Mexican hat. wondering best practices...

1. mow it now in the fall down short

2. Then in the spring apply an herbicide?

3. do you have a couple of referrals for contractors to do both?



8744 Golden Fields Lane

Loveland,Co. 80538


Larimer County Colorado

1 Response

Hi John,

The following is a link to the Colorado Department of Agriculture Noxious Weed species identification website to be sure you have musk thistle before you implement a management plan: https://www.colorado.gov/pacific/agconservation/noxious-weed-species Musk thistle (Carduus nutans) is a Colorado Noxious Weed List B species. Click on the image for musk thistle to pull up the fact sheet for additional information and management practices. A combination of management practices is recommended for control.

CSU Extension also has the following fact sheet on musk thistle: http://extension.colostate.edu/docs/pubs/natres/03102.pdf. Musk thistle reproduces only by seed, so keeping the seed from the soil and depleting the soil seed bank are key to its control. Depending on how much thistle you have, you will want to remove and bag the seed heads to prevent seed spread. Mowing is effective, however, the flower head will need to be bagged and disposed of since flowers can mature even after cut. The CDA and CSU fact sheets provide herbicide recommendations, which should be applied in the spring when the plant is in the rosette stage.

Prairie coneflower or Mexican hat (Ratibida columnifera) is a native perennial plant in Colorado. Here is the link to the USDA Plant’s Database with information on prairie coneflower: https://plants.usda.gov/factsheet/pdf/fs_raco3.pdf. Because this is a native plant, I was not able to find research based information on control methods. Prairie coneflower can spread by seed so keeping the seed from the soil bank will help reduce the spread.

CSU Extension has a Small Acreage Service Database: http://sam.ext.colostate.edu/. The Larimer County Weed District also has a list of contractors: http://www.larimer.org/weeds/. Click on “Applicators, Consultants, Mowers, Seed Companies” in the right hand column.