BREAKTHROUGH IN BATTLE AGAINST PROBLEM PONTICUM

A new weapon is being deployed in the battle against one of Britain's most invasive alien plants, Rhododendron ponticum.

Stem injections are being used to tackle giant bushes of the evergreen plant, which thrives in the acid soils and wet climate of the west coast.

Since being planted extensively as shelterwood in Victorian times, the hybrid Rhododendron ponticum has spread rapidly, blanketing countryside with impenetrable foliage and choking out native wildlife. However in recent years, land managers have been fighting back in a bid to reclaim the dark rhododendron jungles and boost biodiversity.

Large, mature bushes have proved the toughest to tackle. They can grow to seven or eight metres tall and produce up to a million seeds a year. But now scientists from Forest Research, the research agency of the Forestry Commission, have come up with a way to stop these monsters in their tracks.

Project leader Colin Edwards of Forest Research explained:

"Flailing or cutting and burning are methods traditionally used for control of rhododendrons, and these are often backed up by spraying of herbicide. However the green rhododendron is difficult to burn, and the largest bushes, which have stout, sturdy stems, are just too tough to be tackled in this way.

"Injecting the herbicide directly into the stem results in the death of the bush within six months. After that the dead material will have dried out and lost its foliage and be much easier to remove. And application of the herbicide is precise - unlike with spraying, it is unlikely to be washed away by rain or affect other surrounding plants.

"The largest and oldest bushes will be producing the most seed and pose the greatest threat to long-term eradication of Rhododendron ponticum in the seed catchment area - removing them removes that threat."

The stem-injection method has been successfully trialled at Inverewe estate in Wester Ross, owned by the National Trust for Scotland. This magnificent lochside site is renowned for its garden, with its collection of some 1000 varied rhododendrons, which pose no threat and are a huge draw for visitors, particularly during the flowering season. Even Rhododendron ponticum is on display, kept under control as a useful and resilient salt-tolerant hedge. But the wider estate has been plagued by the expansion of invasive ponticum.

Rob Dewar of Inverewe said

“The National Trust for Scotland has been tackling the problem of

Rhododendron ponticum

for many years on a number of its properties, including Inverewe. The bush provides an effective shelter-belt against the coastal winds, and for this reason was first planted at Inverewe Garden by its Victorian founder, Osgood Mackenzie.

“Conservation volunteers have been providing much of the manpower to cut the ponticum that has spread from the Garden into the surrounding woodlands. The problem is, cut rhododendron requires follow-up spraying, which demands a lot of time from limited staff resources. On top of this the opportunities to carry out spraying operations are often limited owing to wet weather, and the effort spent is not always successful.

"Andrew Jackman, the Woodland/estate Manager at Inverewe, has been trialling the injection method with some very positive results, so that we will now be using this where possible in future. It has the advantage of being many times more cost-effective, uses very little chemical and, not least, eliminates the need to walk over rough terrain with a 20-litre chemical knapsack. All that is required is a battery drill and a small amount of chemical!"

He added: "We have set up an empirical study area, which involves injecting one bush each month. The results will determine the response to treatment during different times of the year. As the problem is so widespread locally, we ran a workshop at Inverewe to which neighbouring estates were invited. Colin Edwards attended and gave a presentation on his research, and we demonstrated the injection technique. There have been a number of requests for information about the technique, so a step-by-step guide has been sent to some estates in response.”

Notes to editors:
1) For further information contact Catriona Ross mobile: 07810 181069 e-mail catriona.ross@forestry.gsi.gov.uk
2) Pictures available from Peter Jolly 07971 285749.
3) Forest Research is the research agency of the Forestry Commission.