Rhododendron
Rhododendron ponticum, Róslabhras
Rhododendron is a high impact invasive species found throughout the country, particularly in the west. It is a member of the Ericaceae family and is native to Asia and the Iberian Peninsula. Rhododendron was introduced into gardens in Ireland around the 18TH century. Rhododendron is a popular ornamental plant known for its large purple flowers. It has escaped cultivation and is now widely established in the wild.
Distribution
(National Biodiversity Data Centre, Ireland, Rhododendron ponticum, image, accessed 11 May 2022)
Rhododendron (Rhododendron ponticum)
Classified as a high impact invasive species by the Irish National Biodiversity Centre. Third Schedule listed species under Regulations 49 & 50 in the European Communities (Birds and Natural Habitats) Regulations 2011
Established
Identification:
- Rhododendron is an evergreen shrub or tree
- Leaves are dark green, shiny and elliptical with a lighter green underside
- The leaves grow around the stem in whorls
- Rhododendron flowers from May-July with showy, lilac-coloured flowers that can also be pink or white. The flowers are bell-shaped, with five lobes and found in clusters.
- Seed pods are produced after flowering
- Woody stems and trunk
Reproduction:
- Rhododendron reproduces sexually and asexually.
- Each Rhododendron shrub can produce up to one million seeds every year.
- These seeds are small and light and easily transported on the wind. They can also be distributed by water or insects. Seeds can also remain dormant for several years and still remain viable.
- Rhododendron also reproduces by vegetative means by layering when the branch comes in contact with the ground and suckering from roots.
- Seed dispersal is the most common way of spread of rhododendron in Ireland.
- Rhododendron does not usually produce flowers until it is 10 to 12 years old.
Impacts:
- Rhododendron can outcompete native species for space and light.
- It forms dense thickets that can choke out native plants. These large thickets can also smother waterways and block vision on roads.
- By colonising an area, the local ecosystem can be altered and lead to possible loss of native species and in turn the fauna that depend on them.
- Rhododendron has also been reported to poison cattle, sheep, and dogs.
- Rhododendron is a carrier of the plant pathogen, Phytophthora ramorum, that causes sudden oak death that can affect several tree species.
Treatment:
- Physical: Rhododendron can be treated mechanically and chemically. Mechanical treatment includes cutting the shrub to the base and uprooting the stumps. This is an effective treatment but can be costly.
- Chemical: Rhododendron can also be treated chemically by the practice of “drill-and-paint,” which involves drilling the plant trunk near the base and the manual application on the fresh surfaces with a Glyphosate based herbicide. This is recommended for larger plants. Smaller, juvenile plants can be foliar sprayed with a Glyphosate herbicide.
- Biological: The fungal pathogen, Chondrostereum purpureum, can be used as a biological control method.
More photos:
