Control of Rhododendron
Rhododendron is an invasive plant species. If it is allowed to spread it can cause damage to important farmland habitats such as woodland, bog and heath in Northern Ireland. Under Cross-Compliance undergrazing is not permitted and farmers or landowners who are in receipt of Single Farm Payment must avoid infestation of their land by species such as rhododendron. In addition agri-environment participants, must control rhododendron to prevent damage to habitats on their land.
This non native species was originally planted in gardens from the 18th century, and on the edges of estate woodlands and heath to provide cover for game. However, the impact of its dark evergreen canopy and toxic leaf litter has produced a sterile zone underneath the plant where native plant species have been unable to compete. Rhododendron is toxic to mammals and insects, and is generally avoided by grazing stock. As few as three leaves can be fatal to sheep and goats. Chemicals are also released into the soil further reducing native plant species and affecting insect, mammal, and bird populations.
One of the management requirements of woodland habitats in the NI Countryside Management Scheme (NICMS) is the removal of all invasive species. Cutting rhododendron results in vigorous re-growth so control must involve herbicide treatment by immediately painting the freshly cut stumps with glyphosate (20 percent solution) or Triclopyr (8 percent solution). Alternatively the stumps may be later drilled and herbicide solution (as above) applied, or the re-growth sprayed with glyphosate in spring after a winter cut.
Rhododendron can spread by suckering from roots and layering when the branches touch the ground, but plants are generally over ten years of age before they produce seeds. As a mature plant they produce over one million windblown seeds each year so control should be initially targeted at the oldest largest plants to reduce further seed release. In later stages of control young seedlings may be hand pulled or saplings sprayed with glyphosate if less than 1.3m tall. Beware of cutting young plants and missing herbicide treatment as these plants will then produce seed within three years. Control projects are successful if the guidelines are followed.
For further information contact your local Countryside Management office.
Rhododendron is a host for the serious plant health disease “sudden oak death”, and is destroying important woodland, bog and heath habitats
