The overall habit of M. heterophyllum is described by the Washington State Noxious Weed Control Board (2007): M. heterophyllum is a submersed rooted macrophyte typically with both submerged and emergent leaves growing from a stout stem up to 3 mm in diameter and 100 cm in length. Stem colour ranges from dark red to brownish red.
Submerged leaves are feather-like, green and 2-5 cm long and 2-4 cm wide, dissected into 7-11 leaflets and arranged into whorls of 4-5 leaves; the highly variable emergent leaves develop during late summer and can reach 5-15 cm above the water; they are 0.4-3 cm long and 1.5-5 mm wide; inflorescence is a spike 5-35 cm long, consisting of flowers in whorls of four; flowers have 4 stamens and petals are 1.5-3 mm long; fruits are 1-1.5 mm in length, round, with 4 chambers (EPPO 2009).
Most of the M. heterophyllum in Bashan Lake, East Haddam, Connecticut, United States occurred in shallow protected areas less than 3 m deep (Bugbee et al. 2003). It is reported by the European and Mediterranean Plant Protection Organisation (2009) to grow in waters up to 1.8 m deep but can apparently grow in water as deep as 4.5 m (Department of Conservation and Recreation Massachusetts 2005).
Principal source:
Compiler: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Review: LeeAnn M. Glomski, U.S. Army Engineer Research and Development Center
Publication date: 2011-03-31
Recommended citation: Global Invasive Species Database (2024) Species profile: Myriophyllum heterophyllum. Downloaded from http://www.iucngisd.org/gisd/speciesname/Myriophyllum+heterophyllum on 02-11-2024.
In the northeastern United States Native submersed monocots such as pondweeds (Potamogeton spp.) and horned pondweed (Zannichellia palustris) and native dicots such as alternate-flowered watermilfoil (M. alterniflorum) and Farwell’s watermilfoil (M. farwellii) may require protection from competition from invasive species (New Hampshire Natural Heritage Inventory 1998, in Getsinger et al. 2003).\n
Preventative measures: Preventative management efforts have focused on the establishment of laws that require removing plant debris from boats and trailers (Thum & Lennon 2006). \r\n
Early detection and treatment is critical for limiting the spread of invasive aquatic plants (Moody & Les 2007, in Thum & Lennon 2010). However many taxa in this clade display high plasticity and similarity in vegetative form. Thum and colleagues (2006) developed a restriction enzyme assay that distinguished M. heterophyllum from native milfoils (Thum et al. 2006). Also a DNA marker has been used to differentiate the invasive M. heterophyllum and its hybrid M. heterophyllum x M. laxum from native taxa (Moody & Les 2010). \r\n
Models that predict the likelihood of invasion are required to aid the prioritisation of monitoring, and reduce associated time and costs. It was found that M. heterophyllum occurs almost exclusively in ‘‘higher order’’ lakes characterised as large, low elevation systems with relatively high pH, alkalinity and conductivity in New Hampshire (Thum & Lennon 2010).
The Department of Conservation and Recreation Massachusetts (2005) has produced an informative document entitled Rapid Response Plan for Variable Milfoil in Massachusetts.
Manual: Hand-pulling or tarping may control infestations (Washington State Noxious Weed Control Board 2007). Hand removal and benthic mat use were more effective than cutting at eight infested lake sites in Maine (Bailey et al. 2008). Benthic mats are an appropriate option for thick extensive infestations, whereas hand removal is more cost-effective and more efficient in areas with small high-density infestations or for selective removal of sparse infestations in native macrophytic strands.
Physical: Drawdown can also be used to control M. heterophyllum where applicable if it is extensive enough to prevent re-growth from seeds (EPPO 2009). This control method could have a negative impact on native plants and animals (EPPO 2009). \r\n\r\n
Chemical: Similar to fluridone newer chemicals tend to be enzyme-specific compounds with a reduced impacts on non-target species (Getsinger et al. 2008). Diquat dibrominde (Reward) and 2,4-D (Aqua Kleen and Navigate) are currently approved for use in most states in North America (Washington State Noxious Weed Control Board 2007). Triclopyr may be another option. Results from Getsinger et al. (2003) suggest that triclopyr may be efficacious against M. heterophyllum in the field over a wide range of concentrations and exposure times. Glomski and Netherland (2007) found that diquat at 370 μg ai L-1 for 30 hours provided good control (85%) of M. heterophyllum and that all rates and exposures of carfentrazone significantly reduced M. heterophyllum biomass, however, shoot regrowth from root crowns required follow-up applications. Fluridone and penoxsulam were also reported to control M. heterophyllum at rates as low as 5 and 10 µg ai L-1 respectively (Glomski & Netherland 2008). \r\n
Biocontrol: Sheldon and Creed (2003) found that the North American weevil Euhrychiopsis lecontei being used as a biological control agent for Eurasian watermilfoil (M. spicatum) is a specialist herbivore which will have little impact on the survival of M. heterophyllum.