Eurasian milfoil and parrotfeather _class B designate_

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					Eurasian water milfoil and parrot feather (Class B designate):
By: Weed Board Staff

           Almost all of the questions that we get concerning aquatic weeds are about milfoil, of which several species
occur in San Juan County. While most local milfoils are natives, two species, Eurasian milfoil (Myriophyllum
spicatum) and parrot feather (M. aquaticum) are introduced invasives and listed as Class B designate weeds. The
submerged leaves of the native and Eurasian water milfoils are in whorls of three to five and are finely dissected. The
easiest way to distinguish between the water milfoils is to note the number of segments on each under water leaf: the
Eurasian species usually has 30 or more lobes while the native species have less than 26, although there are instances of
overlap in this characteristic. In this case, it may take DNA analysis to distinguish the species. Parrot feather, a native
of the Amazon Basin and planted in at least one hobby pond in the county, has most of its leaves above water and 20-
30 somewhat fleshier lobes per leaf. Its underwater leaves are largely decomposed.
           The two exotic Myriophyllm species reproduce primarily vegetatively through fragments. While Eurasian
milfoil can produce viable seed, seedlings are rarely produced under natural conditions. Parrot feather, outside of its
native habitat, is entirely female and cannot reproduce sexually. Both Eurasian milfoil and parrot feather are capable of
rapid growth, often overtaking a pond or shallow lake from bank to bank within two years of the initial planting.
           Eurasian milfoil and parrot feather pose threats simply because they are so successful. Their rapid and
luxuriant growth shades out all other plant life, including the natural algae in the water column which form the basis of
the food chain. Dense stands of either species provide choice habitat for mosquitoes. The plants can completely
block recreational activities such as boating, swimming and fishing. In the southwestern part of the state, parrot feather
has become an economic problem, costing the Longview Diking District in excess of $50,000 per year to keep
irrigation ditches and canals open.
           Control over small areas of water milfoil can be achieved by the use of opaque barrier fabrics which, when
laid over the bottom, will block photosynthesis. Drawing down a pond about seven or eight feet during freezing
temperatures can prove effective, but may need to be done several times. Yearly draw downs during hot summer
weather, allowing the bottom to desiccate, may also control milfoil. Harvesting or cutting will reduce the burden of
milfoil in a pond, but must be done at least twice a year indefinitely. Harvested remains can be dried and composted.
Since milfoils all reproduce from fragments, it is necessary to remove all the pieces from the pond after cutting.
Extensive research is being conducted on biological control organisms for milfoil. So far, no insects have been
approved for release in Washington, although there is a native weevil that feeds exclusively on native and non-native
water milfoils. Grass carp will eat Eurasian water milfoil, but generally do not prefer it and will eat all other available
plant species before consuming milfoil. They have an even lower preference for parrot feather, so they are not
recommended as a control organism for either species.
             The use of chemicals for aquatic weed control is highly site specific. Although water milfoils are
somewhat susceptible to certain herbicides, it is difficult to achieve control or eradication chemically. All herbicides
registered for aquatic use in Washington are restricted and only may be applied by permit by a licensed applicator. By
law all herbicides must be used in strict accordance with the label instructions.
           As it is with all noxious weed species, the best control is prevention. Do not buy, plant or use Eurasian
water milfoil or parrot feather in your water gardens and never introduce either species into natural lakes or ponds. If
you wish further information please call Rich Lee or Judy Jackson at the County Weed Control Program at 376-3499.




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    1.   Parrot feather: Above water leaves
    2.   Parrot feather: plant structure
    3.   Native water milfoils: submerged leaves
    4.   Eurasian water milfoil: submerged leaves

				
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