Yesterday, I stopped off to view West Dean Brooks, situated in the Cuckmere Valley near Seaford, part of the Seaford to Beachy Head SSSI… I was alarmed by the amount of Parrotfeather growing in the roadside ditch. I recall that some 20 years ago, when part of my remit was a management input into this area, I would occasionally stop-off and carefully hand rake out, the small quantity then growing. Routine mechanical weed clearance by the EA over the years has very likely spread this weed along the main feeder ditch.
No ecological benefits are associated with Parrotfeather ( Myriophyllum aquaticum), it being an introduced specie native to the Amazon in South America. It prefers a warm mild climate although it can survive temperate winters. Parrotfeather grows best in still waters such as lakes, ponds, quiet streams and drainage ditches and is also able to survive in rivers. Vegetative reproduction is the only likely dispersal agent because female plants are not found in the UK. Fragments can be carried by water birds and floodwaters from one location to another.
Parrotfeather readily takes over lakes, ponds and streams outcompeting native plants. It is an especially problematic plant because it is so difficult to control. Once it enters into a water body, it takes a considerable and costly effort to eliminate it.
Parrotfeather provides an ideal habitat for mosquito larvae and the mass of the plant can increase the likelihood of flooding occurring. It may also block passage for fish species when they navigate up watercourses to spawn. In addition, it can cause pH and other water quality issues in still water areas. The tough stems make it difficult to boat, swim or fish.
While Parrotfeather may provide cover for some aquatic organisms, it can seriously change the physical and chemical characteristics of lakes and streams. Infestations can alter aquatic ecosystems by shading out the algae in the water column that serve as the basis of the aquatic food web.
Treatment Options.
Various herbicides are produced which can be applied to aquatic habitats but they are indiscriminate with regard to native plant species, are of course poisons and chemical treatment is expensive and would probably require several applications.
Physical Removal Options.
Mechanical cutting, nets and rakes can be used to control Parrotfeather BUT without great care, fragmentation is very likely to cause further dispersal as even tiny fragments can re-grow. Therefore, mechanical control is not recommended unless the waterbody in question is significantly infested. Cleaning and inspection of machinery and tools before being transported on to another aquatic site is recommended.
Plant Description.
Parrotfeather is an herbaceous aquatic plant that grows to a length of 6.5 to 16 feet. Its stems are greenish blue with numerous small leaves that resemble feathers. The leaves are either submersed or emergent and grow in whorls of 4 to 6 around the stem. This species is easily confused with the native water milfoils but those don’t have above water leaves.
Look for:
- Bright green fir-tree-like; emergent leaves and stems
- Leaflets arranged in whorls (4-6) around the stem
- Leaflets with feather-like leaf arrangement
- Dense mat of intertwined brownish stems (rhizomes) in the water
- Reddish, feathery-leaved, limp, underwater leaves may be present