Myriophyllum spicatum

Species of flowering plant in the family Haloragaceae

Myriophyllum spicatum (Eurasian watermilfoil or spiked water milfoil) is a submerged aquatic plant which grows in still or slow moving water. It is native to Europe, Asia, and North Africa, but has a wide geographic and climatic distribution among some 57 countries, extending from northern Canada to South Africa. It is considered to be a highly invasive species.

Myriophyllum spicatum produces ellagic, gallic and pyrogallic acids and (+) catechin, allelopathic polyphenols inhibiting the growth of blue green alga Microcystis aeruginosa.

Myriophyllum spicatum is found in disperse regions of North America, Europe, Asia, Australia, and Africa. where it has become an invasive species in some areas. By the mid 1970s, watermilfoil had also covered thousands of hectares in British Columbia and Ontario, Canada, and spread some downstream via the Columbia River system into the Pacific Northwest of the United States.

In lakes or other aquatic areas where native aquatic plants are not well established, the Eurasian plant can spread quickly. Eurasian watermilfoil grows primarily from broken off stems, known as shoot fragments, which increases the rate at which the plant can spread and grow. In some areas, the Eurasian Watermilfoil is an Aquatic Nuisance Species.

The aquatic moth Acentria ephemerella, the water veneer moth, feeds upon and damages this water milfoil. It has been used as an agent of biological pest control against the plant in North America. The milfoil weevil (Euhrychiopsis lecontei) has also been used as biocontrol. Another method for biocontrol is Grass Carp, (one of the Asian Carp species) which have been bred as sterile, is sometimes released into affected areas, since these fish primarily feed on aquatic plants and have proven effective at controlling the spread. However, the carp prefer many native species to the milfoil and will usually decimate preferred species before eating the milfoil. In Washington State the success rate of Grass Carp has been less than expected. They were used in 98 lakes and 39 percent of them had no submerged plant life left after only a short time. Since roughly 2000, hand harvesting of invasive milfoils has shown much success as a management technique. Several organizations in the New England states have undertaken large scale, lake wide hand harvesting management programs with extremely successful results. Acknowledgment had to be made that it is impossible to completely eradicate the species once it is established. As a result, maintenance must be done once an infestation has been reduced to affordably controlled levels. Well trained divers with proper techniques have been able to effectively control and then maintain many lakes, especially in the Adirondack Park in Northern New York where chemicals, mechanical harvesters, and other disruptive and largely unsuccessful management techniques are banned. After only three years of hand harvesting in Saranac Lake the program was able to reduce the amount harvested from over 18 tons to just 800 pounds per year. In order to prevent damages from mass growth of the plant in lakes, the water level can be lowered. By freezing out the bottom of the bank in the winter months, the population of the plant decreases.

Trailering boats has proven to be a significant vector by which Eurasian milfoil is able to spread and proliferate across otherwise disconnected bodies of water. Effective methods for mitigating this spread, are visual inspections with subsequent hand removal or pressure washing upon boat removal. In the Okanagan River Basin of south central British Columbia, a specially adapted rototiller is used to dredge shallow water to damage or destroy the root system.