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How can the Fringe Lily be controlled?

LOCHMABEN LOCHS SITE OF SPECIAL SCIENTIFIC INTEREST (SSSI),
MILL LOCH, FRINGED WATER LILY CONTROL

Over the last two spraying seasons members of the Lochmaben Initiative have undertaken 8 spraying sessions on the loch (2 in 2006 and 6 in 2007). The spraying had a dramatic impact on the lily which died off soon after being treated. Despite this initially encouraging result, in 2007 the lily was found to have regenerated in those areas which were sprayed in 2006. This trend has been seen many times over the last decade and is expected to occur again next year on those areas that were sprayed this summer. The map shows the 2007 extent of the lily.

The lily is continuing to spread and there is now a new area along the north western shore. It is a concern as that the chemical currently being used, glyphosate, is not providing effective control. This was confirmed recently by the Centre for Aquatic Plant Management (CAPM), a research body who specialise in providing advice on the control of problematic aquatic and waterside plant species. They tested the use of glyphosate on the lily and concluded that it cannot be relied upon to provide effective control.

As a result of observation and through discussion with freshwater experts from SNH and CAPM, a different approach is to be tried. In 2008, it is intented to undertake a trial of a different chemical, dichlobenil. Dichlobenil comes in a granule form and is scattered into the water where it sinks to the bottom and is taken into the plant through its roots. This method kills the plant from the root up as opposed to from the leaf down, as in the case of glyphosate. Research undertaken by CAPM shows this to be significantly more effective in controlling the lily.

Dichlobenil is a more powerful chemical which is likely to impact on other plant species, is moderately toxic to fish, water flea, and algae, and has a half life of approximately 2.8 years. This mean that is potentency reduces by half in that time.

It is felt that this is an acceptable risk as the alternatives i.e. continue to use glyphosate, or do nothing, is likely to result in the continuing spread of the lily until it reaches a point where it will cover about 25% of the loch surface (see map) This will result in impacts on other plant species and perhaps some of the birds and insects too. Additionally, recreational activities such as fishing may become be severely restricted. The trial of dichlobenil will cover an area of approximately 10m x 50m in the north and will be carried out in March 2008. A further trial area similar in size in the north-west will have four sections—glysophate + sticking agent; dichlobenil; control area; glysophate. Buoys and stakes would mark the limits.

For the remaining areas of the loch it is intended to continue to use a glyphosate solution but one with a new soya based sticking agent added. When sprayed onto the leaves of the lily, the solution adheres to the leaf surface and slowly releases the glyphosate. Research shows that it can significantly improve the effectiveness of glyphosate as it isn’t getting washed off the leaves. The agent is completely non-toxic and if successful, may be sufficient to achieve effective control of the lily on Mill loch in future.

The continued growth of the lily also poses a risk to Castle Loch. If fragments of the lily escape from the Mill loch and enter the Castle Loch, it could have very serious implications. To try and address this issue the area where water from the loch enters the Marjorie Sike/Innerfield Burn is to be managed. In practice this will mean that all water leaving the loch will run through a hessian filter which will trap any parts of the lily escaping from loch. The build up of material behind the filter will be removed periodically.

The Mill loch forms part of the Lochmaben Lochs SSSI and is noted for its open water habitat, its areas of open water/fen transition, and its invertebrates. The aim of SNH is to maintain these features and return the loch to as natural an area as possible.