Noxious weeds are a danger to our environment and the economy. They can take over entire ecosystems, destroy natural habitats, damage agricultural production, and cause losses worth millions of dollars. As they spread to natural areas, they can harm wildlife by crowding out native plants that these ecosystems depend on. Left unchecked, these invasive species can be nearly impossible to eradicate. 

Some of Colorado's noxious weeds can produce more than 300,000 seeds per plant, and each seed can be viable for up to 20 years while it seeks out the ideal location and conditions for germination! Each plant that is eradicated can have a lasting impact. 

Yes. The State of Colorado as well as Silverthorne Town Code requires every owner, tenant, or occupant to control the growth of noxious weeds on their property. Per Town Code, property owners who fail to control noxious weeds can be fined up to $300 per day. To avoid fines and additional incurred costs, please take steps to control weeds on your property and prevent them from spreading to neighboring lands. 

Many of the HOA's in Silverthorne have programs in place that will control noxious weeds on your property. Your HOA may allow you to opt out of these programs, but you are still responsible for controlling these weeds. 

Seeds can be washed onto property by creeks or drainage ways, carried by birds and other wildlife in their digestive tracts, carried by wind, or transported many miles in topsoil or landscaping plants. 

It is important to note that there is no "one-and-done" or "one-size-fits-all" treatment for noxious weeds. Please see the list of common weed species above for the preferred method of eradication. Some are easy to pull, while others spread by underground roots. Not all seeds germinate at the same time. Some seeds from previous seasons may germinate as soon as the snow melts, while others may not germinate until September. Effective noxious weed removal requires consistent treatment and monitoring throughout the growing season, generally May through September, and year after year. 

If you are not a full-time summer resident at your property, please contact your HOA for more information on how to have weeds on your property identified, treated, and monitored. Most HOAs may coordinate noxious weed control in your absence. If you are not a member of an HOA, please contact a licensed professional from the list of approved Summit County weed contractors. 

Stay up to date with Silverthorne Town news for more information on noxious weeds and upcoming community weed pulls. 

• Silverthorne Noxious Weed Code 
• Summit County Weed Control 
• State of Colorado Noxious Weed Program

Scentless Chamomile 

• Identification: Flowers are small, dime-sized and daisy like. White petals are arranged around a yellow center, leaves are soft and fern-like. Mature plants can grow 1 to 3 feet tall and each plant can include 100 flowers or more. 
• Reproduction: By seed only 
• Life Cycle: Annual, plant dies at end of first season after seed dispersal 
• Eradication Goal: Prevent flower production and dispersing of seeds 
• Mechanical Eradication Method: Shallow root system makes this weed very easy to pull. Any mature plants with flower heads should be bagged, carried offsite and thrown in the trash. 
• Chemical Eradication Method: Contact a weed control specialist for more information. 

Musk Thistle 

• Identification: Large tennis ball-sized purple flowers that "nod" when mature. Typically one flower per stem and mature plants grow 4 to 6 feet tall. 
• Reproduction: By seed only 
• Life Cycle: Biennial (flat rosette first year; bolts upright during second year producing flowers and seeds; plant dies at end of second year after seed dispersal; seeds can continue to mature even after the flower bud is severed. 
• Eradication Goal: Prevent flower production and dispersing of seeds. 
• Mechanical Eradication Method: Severing the taproot just below ground level with a hoe or shovel is very effective at ending the plant's life cycle. Any buds or mature flower heads should be bagged, carried offsite and thrown in the trash. 
• Chemical Eradication Method: Contact a weed control specialist for more information. 

Note: Do not confuse Musk Thistle with Summit County's native thistles (Eaton's and Ousterhout's). These native thistles typically have smooth, dark red stems. Find more information about Colorado's native thistles here. 

Canada Thistle 

• Identification: Soft, dime-sized, lavender-colored flowers; multiple flowers per stem; mature plants grow 2 to 4 feet tall; flowers are smaller than those of Musk Thistle and are often found along river banks, ponds, lakes, springs and seeping soils. 
• Reproduction: By seed and horizontal roots 
• Life Cycle: Perennial (plant comes back year after year); seeds can continue to mature even after the flower bud is severed. 
• Eradication Goal: Prevent underground spread of roots, flower production and dispersal of seeds
• Mechanical Eradication Method: Horizontal roots can spread up to 15 feet in all directions and 6-15 feet deep, making mechanical removal virtually impossible. 
• Chemical Eradication Method: Contact a weed control specialist for more information. After chemical treatment, any mature flower heads should be bagged, carried offsite, and thrown in the trash. Because plants can utilize abundant nutrients stored in roots, repeat treatments may be required for one to two years. 

Common Mullein

• Identification: Large wooly, grey-green leaves when mature, yellow flowers on a tall terminal spike, mature plants grow 2 to 6 feet tall and 2 to 3 feet wide at the base. 
• Reproduction: By seed only
• Life Cycle: Biennial. Flat wooly rosette first year that is 1 to 2 feet in diameter, bolts upright during second year producing flower spike and seeds, plant dies at end of second year after seed dispersal. A single plant can produce up to 250,000 seeds which can continue to mature even after the root is severed. 
• Eradication Goal: Prevent flower production and dispersal of seeds. 
• Mechanical Eradication Method: Severing the taproot just below ground level with a hoe is very effective at ending the plant's life cycle. Any buds or mature flower heads should be bagged, carried offsite, and thrown in the trash.
• Chemical Eradication Method: Herbicides are most effective before the plant bolts upright. Wooly leaves reduce the effectiveness of herbicides. Contact a weed specialist for more information. 

Yellow Toadflax

• Identification: Narrow, linear leaves 1 to 2 inches long, flowers are pale yellow with an orange center and form on a single terminal flower head. Mature plants grow upright 1 to 3 feet tall and 1 foot wide at the base. 
• Reproduction: By seed and spreading roots. 
• Life Cycle: Perennial (plant comes back year after year). Seeds can continue to mature even after the flower bud is severed. 
• Eradication Goal: Prevent underground spread of roots, flower production and dispersal of seeds. 
• Mechanical Eradication Method: Roots can grow 3 feet deep and 12 feet wide, rendering pulling, digging, and flower head removal ineffective. Severing the above-ground plant encourages spread of root system. 
• Chemical Eradication Method: Herbicides are generally effective throughout entire life cycle. Contact a weed control specialist for more information.