The plant's scientific name says it all. Myriphyllum spicatum broken down means “plant with
many leaf divisions that bears flowers in a spike”. These flower spikes are what often gives this plant away, especially in the later portion of the growing season when the plant becomes "topped out" and is most problematic.
|EWM can cause a number of problems including prop fouling. |
Photo Credit: Brett Hartis
Since the 1940s, Eurasian watermilfoil has become a major problem for mid-atlantic, and midwestern states. The hydropower and flood control reservoirs of the Tennessee River have dealt with the plant for a number of years, warranting large-scale applications of herbicides to eradicate the weed. Eurasian watermilfoil is still present in the TVA (Tennessee Valley Authority) system but has largely been displaced by hydrilla, which we discussed in our last plant profile. Since the 1980's the species has invaded lakes in Idaho, Minnesota and Maine making it the most widespread submersed aquatic weed in the northern half of the US.
|Above surface flower spikes common of EWM.|
Photo Credit: Texas A&M AQUAPLANT
EWM is commonly found in water as deep as 15 feet but can survive much deeper when more light is available in extremely clear water. Eurasian watermilfoil is designated as an evergreen perennial plant that produces biomass year round and overwinters as root crowns. EWM is often confused with native species of milfoil, and has even been noted to hybridize with certain species! Its leaves are feather-like, with each leaf composed of 14 to 24 pairs of leaflets arranged in whorls of four. Stems and plant tips can appear reddish, but this can often vary. Reproduction of the plant can occur through seed, but is most likely accomplished through fragmentation, which is common among submersed plants.
Several herbicides can be used to effectively manage Eurasian watermilfoil. Contact herbicides –
including diquat and endothall – provide good control, whereas systemic herbicides such as 2,4–D,
fluridone and triclopyr provide excellent control. Mechanical controls can provide temporary relief at relatively small sites and physical controls such as drawdowns, where applicable, can reduce the ability of EWM to survive.
For more information on Eurasian watermilfoil, including management options, visit our BMP Manual page 121.
For a current distribution map of EWM, visit the Eastern Forest Threat Center EWM page
For more on the Aquatic Ecosystem Restoration Foundation, visit our website.
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