Scotch thistle (Onopordum acanthium) is a noxious weed that can quickly take over lawns, gardens, and pastures. Its spiny leaves and large, purple flowers make it a particularly aggressive invader. Effective control of Scotch thistle requires the use of herbicides that target this tough, deep-rooted plant without harming desirable plants.

In this guide, we’ll explore the best herbicides for controlling Scotch thistle and offer tips for selecting the right product for your needs. Whether you’re dealing with a few plants or a widespread infestation, these herbicides can help you restore your landscape to its original condition.

Best Herbicides for Scotch Thistle

1. Crossbow Herbicide

Crossbow is one of the most effective herbicides for controlling Scotch thistle. This broad-spectrum herbicide contains a combination of triclopyr and 2,4-D, which work together to control a wide variety of weeds, including Scotch thistle.

Crossbow is a systemic herbicide, meaning it is absorbed by the plant and moves through its vascular system to kill the roots. It is highly effective when applied to actively growing Scotch thistle, and its long-lasting effects prevent regrowth.

2. Tordon RTU Herbicide

Tordon RTU is a highly concentrated herbicide that is effective against Scotch thistle, as well as other deep-rooted weeds. It contains picloram, a powerful systemic herbicide that targets tough weeds and prevents them from regenerating.

Apply Tordon RTU directly to the foliage of Scotch thistle for quick results. This herbicide is ideal for large-scale infestations, but it must be used carefully as it can harm desirable plants if applied improperly.

3. Milestone Herbicide

Milestone is a selective herbicide that works well on Scotch thistle and other broadleaf weeds. It contains aminopyralid, which interferes with the plant’s ability to grow and reproduce, causing it to die over time.

Milestone is highly effective on Scotch thistle, even when the plant is established. It has a low environmental impact, making it a good option for areas where you want to avoid harming surrounding vegetation.

4. Garlon 4 Herbicide

Garlon 4 is a powerful herbicide containing triclopyr, which is effective against Scotch thistle and other woody plants. It is a systemic herbicide that targets the plant’s vascular system, killing both the foliage and roots.

Garlon 4 is highly effective in controlling Scotch thistle, especially in areas with dense infestations. However, it should be applied with care, as it is a non-selective herbicide that can damage surrounding plants.

5. Chlorsulfuron Herbicide

Chlorsulfuron is a selective herbicide that is effective against broadleaf weeds like Scotch thistle. It is absorbed by the plant and works by inhibiting protein synthesis, ultimately killing the plant.

Chlorsulfuron is a great option for controlling Scotch thistle in areas where you want to preserve other vegetation. It is commonly used in pasture and rangeland settings.

6. Remedy Ultra Herbicide

Remedy Ultra is a highly effective herbicide for controlling Scotch thistle and other tough woody plants. It contains triclopyr, which targets the plant’s root system to ensure long-lasting control.

Remedy Ultra is an excellent choice for large-scale infestations of Scotch thistle. It is particularly effective in areas with high moisture, where Scotch thistle thrives.

7. Crossbow Specialty Herbicide

Crossbow Specialty is an effective herbicide for controlling Scotch thistle. It is similar to Crossbow, but it is formulated to be more effective in a variety of environmental conditions, including humid and wet areas.

This herbicide is ideal for controlling Scotch thistle in areas with dense vegetation or high moisture. It is particularly effective in difficult-to-treat areas.

8. Clopyralid Herbicide

Clopyralid is a selective herbicide that targets broadleaf weeds like Scotch thistle. It is absorbed by the plant and inhibits growth, eventually causing the plant to die.

Clopyralid is effective against Scotch thistle, especially when applied during the plant’s growing season. It is often used in pasture management programs.

9. Tordon 22K Herbicide

Tordon 22K is a potent herbicide that is effective against Scotch thistle and other deep-rooted weeds. It contains picloram, which works by disrupting the plant’s ability to grow and reproduce.

Tordon 22K is ideal for treating large infestations of Scotch thistle. It is highly effective but should be used with care, as it can harm desirable vegetation if not applied carefully.

10. Aminopyralid Herbicide

Aminopyralid is a selective herbicide that targets tough, deep-rooted weeds like Scotch thistle. It works by interfering with the plant’s growth and preventing it from regenerating.

This herbicide is highly effective against Scotch thistle, and it is often used in pasture and rangeland management programs.

Buyer’s Guide: Choosing the Best Herbicide for Scotch Thistle

When choosing the best herbicide for Scotch thistle, consider the following factors:

1. Type of Herbicide

Systemic herbicides like Tordon RTU and Crossbow work by being absorbed by the plant and traveling to the roots to kill the entire plant. These are highly effective for deep-rooted weeds like Scotch thistle.

2. Selectivity

Some herbicides, such as Milestone and Chlorsulfuron, are selective and target only Scotch thistle, leaving desirable plants unharmed. Non-selective herbicides, like Crossbow Specialty, should be used with caution as they can kill other vegetation.

3. Application Timing

It’s essential to apply herbicides when Scotch thistle is actively growing for the best results. Pre-emergent herbicides are not effective against Scotch thistle as it is a biennial plant that grows from seed.

4. Safety

If you are concerned about the environmental impact, look for herbicides with lower toxicity to non-target plants and wildlife. Always follow label instructions for safe application.

5. Cost

The cost of herbicides can vary depending on the product and the size of the area you need to treat. Larger infestations may require more herbicide, so it’s important to choose a product that fits your budget.

Conclusion

Scotch thistle can be a challenging weed to control, but with the right herbicide, you can effectively manage it. Whether you choose a systemic herbicide or a selective product, following the label instructions and applying the herbicide at the correct time is key to success. Consider your specific needs, the size of the infestation, and the safety of the surrounding environment when making your choice.

With the right herbicide, you can regain control of your landscape and prevent Scotch thistle from taking over your yard or garden.