Parrots feather – Myriophyllum aquaticum – First found in the UK in the 1960’s Parrots feather is an alien invasive species. Parrots feather is native to central South America. It can now be found in up to 300 sites across the UK. While it has mostly be found in ponds there have been instances of it living in gravel pits, reservoirs, canals, streams and ditches. Unlike other plants from the same genus parrots feather has the ability to continue growing when ponds and waterways dry out. Its characteristic feathery appearance it producing both emergent shoots as well as submerged ones. The plant spreads by asexual means; this is because it is only the female plants that have established within the United Kingdom. The plants stems are quite brittle and the plant propagates itself through the growth of small fragments from the parent plants.
Unfortunately the species is sold by nurseries and aquatic garden centres and as a result is grown in many ponds right across the UK. Garden centres also often sell M. propernaciodes, or M. brasiliense, or M. propium – these should be avoided as all are highly invasive species as well. Parrots feather has now become established in Austria and France, as well as the UK. It is not believed that the introduction of these plants has been deliberate, but that small fragments of the plant have been transferred via the soil of other purchased aquatic plants.
- Mechanical control – Mechanical control via weed cutting boats has been found to be an effective method for removing large infestations of this plant. However, it is important that great care is taken to prevent any stem fragments (the stems are very brittle and fragmentation happens easily) from floating downstream as their regrowth is rapid. Care should be taken to restrict the downstream movement of stem fragments which will result from cutting operations as regrowth is rapid.
- Chemical control – The plant is controlled by applications of glyphosate late in the season, and also to some extent by applications from April onwards. Short term elimination of parrots feather can occur from chemical control, however recolonisation from original sources will often take place. Because of this it is important to try to eliminate the infestation at the source.
- Biological control – Grass carp will not eat this species unless they are at least 2 years of age and then only reluctantly as long as no other preferred species are present.
- Environmental control – Parrots feather does not cope well in fast flowing waters. By narrowing channels of slow flowing water to increase flow speed one can restrict any further growth. Additionally this species can also be controlled by increasing shade – either by placing a floating opaque material over the infestation during spring or by planting trees on the south side of the water. To achieve success via control by shade one must maintain the shaded area for at least tweleve months. Another form of control can be achieved by reducing the nutrient level in the water – this will encourage native species to grow and reduce the stranglehold that the parrots feather has on the waterway. There are several ways to reduce the nutrient levels including reducing phosphates from sources such as farm effluents and sewage works.
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