Colorado is home to breathtaking landscapes, diverse ecosystems, and a variety of native plants. However, many of these ecosystems are under threat from invasive plant species that spread aggressively and choke out native vegetation.
These unwanted plants reduce biodiversity, affect soil quality, and create challenges for both landowners and conservationists. Invasive plants in Colorado compete with native species for sunlight, water, and nutrients.
They spread quickly, often forming dense monocultures that destroy natural habitats. Farmers, ranchers, and homeowners alike are forced to spend significant resources to manage and control these species.
The good news is that with proper awareness, identification, and use of effective herbicides, invasive species can be controlled. Below is a comprehensive list of the 10 worst invasive plants in Colorado, their characteristics, and recommended control methods.
10 Best Invasive Plants Of Colorado
1. Canada Thistle – Best Herbicide: Milestone Herbicide (Corteva Agriscience)
Canada thistle is one of the most troublesome weeds in Colorado. Its deep root system allows it to regenerate even after cutting, making it hard to eliminate. This species invades pastures, croplands, and natural areas.
It spreads rapidly by both seeds and underground rhizomes. Dense patches reduce forage quality for livestock and hinder native plant restoration. If left uncontrolled, Canada thistle can dominate entire fields.
A highly effective solution is Milestone Herbicide manufactured by Corteva Agriscience. It controls thistles at the root level and provides long-lasting suppression with minimal impact on grasses.
Pros:
• Livestock forage
• Pollinator use
• Hardy plant
• Erosion control
• Wide coverage
• Soil adaptable
• Resilient growth
Cons:
• Invasive spread
• Hard removal
• Low biodiversity
2. Dalmatian Toadflax – Best Herbicide: Tordon 22K (Corteva Agriscience)
Dalmatian toadflax is a perennial weed with bright yellow flowers resembling snapdragons. It thrives in disturbed soils, roadsides, and open rangelands across Colorado. Its waxy leaves make it resistant to some herbicides.
The plant produces thousands of seeds annually, ensuring rapid spread. Its extensive root system allows it to survive tough conditions. Left unchecked, it can displace native grasses and wildflowers.
Tordon 22K, also from Corteva Agriscience, is widely recommended for controlling Dalmatian toadflax. It penetrates deep roots and prevents regrowth effectively.
Pros:
• Attractive flowers
• Drought tolerant
• Hardy perennial
• Erosion control
• Waxy leaves
• Early blooming
• Fast spread
Cons:
• Outcompetes natives
• Hard removal
• Toxic foliage
3. Russian Knapweed – Best Herbicide: Perspective Herbicide (BASF)
Russian knapweed is another serious invasive plant in Colorado. Its gray-green leaves and purple flowers make it easy to identify, but difficult to control. It thrives in pastures, roadsides, and rangelands.
This plant spreads through creeping roots that form dense colonies. It releases toxins into the soil, preventing other plants from establishing. Over time, it creates large monocultures.
Perspective Herbicide from BASF is effective against Russian knapweed. It offers broad-spectrum control and is particularly strong against deep-rooted perennials.
Pros:
• Attractive flowers
• Pollinator support
• Soil coverage
• Fast colonization
• Hardy plant
• Root resilience
• Drought tolerant
Cons:
• Allelopathic
• Livestock risk
• Long persistence
4. Leafy Spurge – Best Herbicide: Plateau Herbicide (BASF)
Leafy spurge is one of Colorado’s most invasive weeds. It produces milky sap that is toxic to livestock and irritating to human skin. Its rapid spread reduces grazing potential on rangelands.
The plant produces both seeds and root shoots, allowing quick expansion. It forms dense stands that crowd out desirable vegetation. Its persistence makes it a nightmare for ranchers.
Plateau Herbicide by BASF has proven effective in managing leafy spurge. It provides both pre- and post-emergent control, suppressing regrowth for multiple seasons.
Pros:
• Bright flowers
• Hardy species
• Erosion control
• Pollinator friendly
• Long-lived
• Low care
• Strong roots
Cons:
• Toxic sap
• Grazing loss
• Spreads rapidly
5. Musk Thistle – Best Herbicide: GrazonNext HL (Corteva Agriscience)
Musk thistle is a biennial weed with spiny leaves and large purple flowers. It thrives in pastures, roadsides, and disturbed areas. Its sharp spines make it unpalatable for livestock.
This plant spreads by wind-dispersed seeds that can travel long distances. Without control, it forms dense infestations that reduce grazing land productivity. It is listed as a noxious weed in Colorado.
GrazonNext HL by Corteva Agriscience is a strong choice for controlling musk thistle. It targets broadleaf weeds while leaving grasses unharmed.
Pros:
• Striking flowers
• Hardy biennial
• Drought tolerant
• Erosion control
• Fast growth
• Seed abundance
• Tall stature
Cons:
• Spiny leaves
• Habitat loss
• Invasive spread
6. Cheatgrass – Best Herbicide: Plateau Herbicide (BASF)
Cheatgrass is one of the most destructive invasive grasses in Colorado. It spreads rapidly across rangelands and forests, altering fire cycles. Its dry, fine stems make wildfires more intense and frequent.
The plant germinates early in spring, outcompeting native grasses. It quickly dries out, leaving behind highly flammable material. Cheatgrass infestations are extremely difficult to manage once established.
Plateau Herbicide from BASF is a proven solution for cheatgrass. It provides selective control and helps restore native plant communities.
Pros:
• Early germination
• Soil coverage
• Fast spread
• Fire fuel
• Hardy species
• Low care
• Adaptable growth
Cons:
• Fire hazard
• Habitat loss
• Hard to control
7. Bindweed – Best Herbicide: Roundup Pro Concentrate (Bayer/Monsanto)
Bindweed is a perennial vine that wraps around crops, fences, and garden plants. It produces white to pink funnel-shaped flowers. While attractive, it quickly strangles and smothers desirable vegetation.
Its deep root system makes it difficult to control. Even small fragments can regrow into new plants. It spreads rapidly in both urban gardens and rural fields.
Roundup Pro Concentrate, manufactured by Bayer (formerly Monsanto), is effective for bindweed. It provides systemic control by killing both the top growth and deep roots.
Pros:
• Attractive flowers
• Soil stabilizer
• Hardy perennial
• Wide coverage
• Root resilience
• Fast spread
• Pollinator use
Cons:
• Smothers crops
• Persistent regrowth
• Difficult removal
8. Common Mullein – Best Herbicide: 2,4-D Amine (Helena Agri-Enterprises)
Common mullein is a tall, fuzzy-leafed weed with a central flowering stalk. It thrives in dry, disturbed soils and often colonizes roadsides and pastures. Its seeds can remain viable for decades.
This species reduces forage quality and competes with native grasses. While some use it for herbal remedies, its invasive nature outweighs benefits. Dense stands make rangeland management difficult.
2,4-D Amine Herbicide by Helena Agri-Enterprises is widely used for mullein control. It works best when applied to young plants before flowering.
Pros:
• Medicinal uses
• Hardy biennial
• Tall structure
• Low care
• Soil adaptable
• Fast growth
• Pollinator use
Cons:
• Seed longevity
• Forage loss
• Invasive growth
9. Kochia – Best Herbicide: Dicamba + 2,4-D (BASF)
Kochia is a fast-growing summer annual found throughout Colorado. It is drought tolerant and thrives in disturbed areas such as roadsides and crop fields. Left unmanaged, it can form dense monocultures.
The plant has developed resistance to several herbicides, making control difficult. Its tumbleweed form allows seeds to spread long distances. This makes it a persistent problem for farmers.
A tank mix of Dicamba and 2,4-D, supplied by BASF, is effective in controlling kochia. It provides post-emergent control and reduces regrowth potential.
Pros:
• Drought tolerant
• Hardy annual
• Fast growth
• Seed abundance
• Soil adaptable
• Forage use
• Easy spread
Cons:
• Herbicide resistance
• Crop invasion
• Invasive spread
10. Yellow Toadflax – Best Herbicide: Escort XP (Corteva Agriscience)
Yellow toadflax, also called butter-and-eggs, is an invasive perennial weed. It produces snapdragon-like yellow and orange flowers. Though visually appealing, it aggressively colonizes pastures and open lands.
The plant spreads by creeping rhizomes and seed production. It quickly displaces desirable grasses and wildflowers. Its waxy leaves make herbicide penetration difficult.
Escort XP from Corteva Agriscience is highly effective against yellow toadflax. It penetrates roots and provides long-lasting suppression.
Pros:
• Attractive flowers
• Hardy perennial
• Pollinator use
• Fast spread
• Soil adaptable
• Low care
• Strong roots
Cons:
• Outcompetes natives
• Hard removal
• Persistent regrowth
Invasive Plants of Colorado FAQs
1. Why are invasive plants a threat in Colorado?
They reduce biodiversity, alter soil chemistry, and disrupt native ecosystems. Invasive species also create economic losses for agriculture and ranching. Left uncontrolled, they can permanently damage landscapes.
2. What herbicides work best for invasive plants?
It depends on the species. Products like Milestone, Plateau, Roundup Pro, and Tordon are proven effective in Colorado when applied correctly. Always follow label instructions for best results.
3. Can invasive plants harm livestock?
Yes. Species like leafy spurge and Russian knapweed are toxic or reduce grazing quality. Ranchers must monitor and control infestations to protect animals.
4. How do invasive plants spread so quickly?
They reproduce through seeds, rhizomes, and creeping roots. Some species also spread via wind, animals, or human activity. Their adaptability gives them an advantage over native plants.
5. Are herbicides safe to use on rangelands?
When applied correctly, yes. Many products target broadleaf weeds while sparing grasses. Safety guidelines and proper timing ensure minimal environmental impact.
6. What non-chemical methods can be used?
Hand-pulling, mowing, grazing, and biological controls are common. However, many invasive species require a combination of methods for long-term control.
7. What native plants can replace invasives?
Colorado blue grama grass, wildflowers like blanketflower, and shrubs such as sagebrush are excellent alternatives. Planting natives helps restore biodiversity and prevent re-infestation.
Conclusion
Colorado’s landscapes are under constant threat from invasive plants such as Canada thistle, leafy spurge, and cheatgrass. These weeds not only disrupt ecosystems but also harm agriculture, ranching, and recreational areas. Identifying them early and applying the right control measures is crucial.
Herbicides from trusted manufacturers like Corteva, BASF, Bayer, and Helena provide effective solutions. When combined with cultural practices, they offer long-term suppression and restoration of native ecosystems.
By understanding the 10 worst invasive plants of Colorado, landowners and residents can take proactive steps. Early intervention is the most cost-effective and environmentally responsible strategy.
Take action today by learning to recognize, manage, and control invasive species on your property. Choosing the right herbicide and replacing invasives with native plants will help preserve Colorado’s natural beauty for generations to come.