Darren Greatbatch, Specialist Advisory Manager, Amenity & Invasive Weeds, at Environment Controls.
Last reviewed on .
We often get asked why is autumn a great time to treat
Giant hogweed?
In this article we’ll explain exactly why autumn a good time to treat and eradicate Giant hogweed.
- After the plant dies back and enters dormancy in late autumn, the soil is more exposed as most vegetation has also died back. This makes it easier to access for physically treating or removal using excavation.
- Frost and freezing temperatures in autumn help degrade the Giant hogweed’s root system – increasing the effectiveness of excavation.
- Although chemical treatments like herbicide spraying are most effective in spring and early summer, targeting late germinating seedlings in the autumn soil seed bank is vital as it helps reduce risk of re-infestation.
- Removal of the dead stems and seed heads is important in autumn because if left untreated they pose a continuing health hazard and source for future growth.
How to deal with Giant hogweed in autumn
Herbicide treatments applied in autumn as a second spray will help to control Giant hogweed. The herbicide Glyphosate is the most widely approved herbicide for Giant hogweed control. Being a broad-spectrum, systemic herbicide, it kills the entire plant, including roots, when applied correctly. Glyphosate is also the only herbicide approved for use near watercourses in many regions.
Important things to note:
- Herbicide application timing is critical – early spring and autumn treatments maximise efficacy by targeting active growth phases and its roots during plant dormancy.
- Multiple applications over a few years are typically necessary to ensure full eradication due to the resilience of its seed banks and roots.
Digging Giant hogweed up in autumn
Mechanical methods like excavation are often used in autumn, when frost and freezing temperatures degrade root stocks and improve control. This timing also allows removal of dead stems and seed heads to reduce hazards and seed spread. However, excavation is usually reserved for large, less sensitive sites due to disturbance and is not suitable for riverbanks or areas with valuable vegetation.
In summary
Autumn treatment leverages seasonal dieback, soil exposure, and cold weather to enhance control of Giant hogweed roots and seeds, supporting integrated, long-term management plans. It’s important to manage Giant hogweed before winter.
Due to the health risk that this plant poses we advise contacting us to get advice and a quote for treatment or removal. We can offer a range of options from a herbicide programme to digging it up. More information here.