- Prevent introduction into new areas - Do not move soil contaminated with seed. If removal of contaminated soil is necessary, seedling emergence can be prevented by burying the soil to a minimum depth of 20 inches (50 cm) and covering it with clean soil - Sowing and planting giant hogweed is PROHIBITED - Since the dispersal of giant hogweed is almost entirely by seeds, it is very important to prevent the plant from setting seed - Control new, smaller infestations first before the seed bank has a chance to establish. - Field technician root-cutting hogweed plants.
Methods Commonly Used
Giant hogweed can be controlled manually, mechanically, and with chemical herbicides. In some cases, a giant hogweed infestation is best controlled using several different methods in combination or in succession - in other words, a two, three, or even four-pronged attack plan. The final part to any control method is to plant grasses or other vegetation to provide competition for giant hogweed and decrease soil erosion.
In order for your control effort to be successful, you will have to ensure that no additional seeds are being introduced to the area. With no influx of seed and a few years of persistent control efforts, giant hogweed plants can be eradicated.
1. Manual & Mechanical Control Methods include root cutting, flower head/seed head removal, cutting and mowing, and cut and cover. Except for root cutting, manual control will not cause immediate death of the plant. All other methods will need two to three treatments per year for several years to deplete the root reserves and kill the plants. All methods will need to occur for multiple years until no new plants grow from the seed bank. Monitor the site for at least three more years to make sure no new seedlings appear.
Start when plants are small and continue mowing throughout season. DO NOT mow if the plants are larger than your mower and NEVER mow if there is a flower or seed head.
If you choose to use this method, the plants must be cut at least three times during a growing season for several years.
Be careful not to spread the seeds - all flower heads should be removed and carefully disposed of prior to mowing.
Mowing equipment should be cleaned before using in another area to avoid spreading hogweed seeds
2. Chemical Application Giant hogweed is susceptible to systemic herbicides, such as glyphosate and triclopyr. The application of these herbicides is considered effective and cost efficient and can be used for the control of a single plant or large stands of giant hogweed. These systemic herbicides will be absorbed by the leaves and will move into the root to prevent regrowth the following year. Triclopyr is a selective herbicide that acts only on broadleaf plants and will not harm grasses in the area. Glyphosate is non persistent in the soil but is also a non-selective herbicide and will kill any surrounding vegetation it comes in contact with. Some triclopyr and glyphosate products (example: Rodeo) are labeled for use in riparian areas and near water. Areas sprayed with triclopyr can recolonize with grasses and other herbaceous species within the same growing season which helps to suppress giant hogweed seedling growth and decrease soil erosion. Recolonization at sites using glyphosate will probably be slower than sites using triclopyr unless re-seeded.
Hard to make the Right choice
Herbicides offer some advantages over mechanical methods. The danger of a person receiving Giant hogweed dermatitis either by direct contact with the plant or indirectly by touching contaminated tools, etc., is much less with herbicidal methods than with mechanical methods.
Control of the weed is usually simpler and more effective by the careful and correct use of herbicides than by mechanical methods (It is almost impossible to remove every piece of underground stem so regrowth is likely to occur.)
However, herbicides may also kill or damage other plants growing nearby.
Several herbicides (chemical weed-killers) have been used effectively for providing good control of Giant Hogweed. However these chemical cannot be use in public parks, school yards or next to water bodies.