American Skunk Cabbage (Lysichiton americanus) produces bright yellow flowers in early spring and can reach up to 1.5 metres in height, forming dense stands which can smother native vegetation and watercourses. Skunk Cabbage is available in garden centres and has been heralded as a “must-have” plant, however its growing presence in the countryside has raised concern. A new EU regulation was agreed in December 2015 which will place stringent controls on this and 13 other plant species. It will become an offence to keep, cultivate, breed, transport, sell or exchange these species, or release them, intentionally or unintentionally, into the environment.
Skunk Cabbage (above, left and right) is becoming an issue in the Tweed catchment
Control methods (June to August)
We trialled 3 different control techniques on American Skunk Cabbage. The trials were conducted on the same day and revisited exactly 3 weeks after initial treatment to assess the effectiveness of each method.
1. Manual removal
Manually dig, and gently pull, until the entire plant and root system has been removed. Skunk Cabbage can spread via rhizome fragments, so it is essential to destroy all of the plant once it is removed. Removal of small/juvenile plants is possible by digging and removing the root system/rhizome. However, this method is not possible if there are many large plants. The root system is half the height of the plant.
2. Foliar spraying of Glyphosate:Water 6l/ha
The chemical is applied to the tops and backs of the leaves thoroughly. The photos below show pre- (left) and post- (right) treatment. After 3 weeks, parts of the plant had died back with the remainder looking unhealthy and yellowing. However some leaves appeared quite healthy post-treatment. This method is not ideal if you are controlling in a sensitive area as the chemical may 'drift' onto non-target species.
3. Core/root treatment using Glyphosate:Water 6l/ha
Using a small spade or planting spear/pinch bar, make a hole in the centre of the plant and administer a 3-5 second spray of the chemical solution. The photo below shows a plant post-treatment. This method uses less chemical and was shown to have a more effective rate of control.