Rhododendron – a further method of control


Originally introduced to Britain from Asia as an ornamental garden shrub, rhododendron Rhododendron ponticum has become naturalised on acidic soils, and is now considered invasive in many areas. Normal methods of rhododendron control during heathland and woodland restoration at Black Down in the Mendip Hills in Somerset (southwest England) had been largely successful, but in some areas of steep terrain or high tree density isolated pockets of rhododendron were difficult to treat. Therefore injection of a herbicide was tested as a possible eradication method.

The trial was initiated in mid-summer when it was thought that there would be a strong flow of sap which would help to transfer the active herbicidal chemicals throughout the treated plants. In dry weather, using a portable electrical drill, a 5 mm diameter hole was drilled 2 cm deep into Rhododendron stems, well below the first branch. Stems with a circumference of over 10 cm had two holes drilled into them. These holes were then filled with glyphosate herbicide.

Five weeks after herbicide injection, the leaves on the treated rhododendrons had browned, tapping of the bushes caused the leaves to fall off and the plants appeared dead. Monitoring of treated bushes for regrowth will continue.
These initial results suggest that this method is an effective way of killing Rhododendron ponticum, and may complement other methods of control typically undertaken in more easily accessible areas.

Note: If using or referring to this published study please read and quote the original paper.

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