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Scientific Name:

Common Name:

Myriophyllum aquaticum (Vell.) Verdc.
Parrot feather watermilfoil
Family: Haloragaceae

USDA Plant Code: MYAQ2

Habitat: Aquatic

Growth Habit: Perennial Forb/herb

Native Environment: South America

Introduction


Problems Caused
Infestations of parrotfeather can choke streams and impede runoff forcing the flooding of adjacent lands. In South Africa parrotfeather infests all of the major river systems where it poses a direct threat to the water supply. In addition, parrotfeather provides mosquito larvae a refuge from predation that may promote the spread of mosquito born disease.

Regulations
Although parrotfeather is not listed on the federal or state noxious weed list, it can cause problems in shallow ditches, streams, ponds, and shallow lakes.

Description



Shoot with Submersed Leaves in the Center,
Surrounded by Shoots with Emergent Leaves
Vegetative Growth
Parrotfeather has both an emergent and submersed growth form. Emergent leaves are whorled, stiff, and usually have 20 or more linear divisions on each leaf. The leaves appear feather-like and grayish green. Vegetative reproduction occurs solely by fragmentation of emergent and/or submersed shoots. Submersed shoots are comprised of whorls of four to six filamentous, pectinate leaves arising from each node. When the submersed shoots reach the water surface, plant growth changes to a horizontal pattern with extensive lateral branching followed by vertical growth of the stem. The horizontal growth results in the senescence of aerial leaves as they become submersed, followed by the growth of emergent shoots and adventitious roots from the rhizome (the original emergent stem) after leaf senescence. Parrotfeather lacks specialized structures for storage, dispersal, and reproduction (e.g. tubers, turions, and winter buds) and therefore rhizomes serve all these functions.

Flowering
Flowers are produced in the axils of emergent leaves. Parrotfeather is a dioecious species (meaning there are separate plants that produce pollen-bearing and ovule-bearing flowers), however only pistillate (ovule-bearing) plants are found outside of South America. Pollen-bearing (staminate) plants are rare even in native populations of South America. For this reason, seed production is not known to occur and reproduction is exclusively vegetative.

Dispersal
The brittle nature of the stems results in many stem fragments that root easily in moist soil to establish new colonies.

Spread By
Parrotfeather is widely used in the horticultural and water gardening trade, as well as an aquarium plant. It is also spread by human activity, on boats and equipment, and by water flow.

Habitat



Typical Infestation of Parrotfeather in a Small Wetland Near Lake, MS
Parrotfeather grows well in shallow wetlands, slow moving streams, irrigation reservoirs or canals, edges of lakes, ponds, sloughs, or backwaters. Parrotfeather is not seriously affected by frost or frequent inundation of salt water; the latter may promote root growth. However, plants growing in northern latitudes may have emergent shoots and leaves killed by a hard frost. Parrotfeather requires rooting in bottom sediment, so environments where light can penetrate to the bottom generally favor colonization. In general, depths of less than 3 feet are optimum; however parrotfeather has been observed growing in waters up to 6 feet deep. Regardless of conditions, once parrotfeather is established it usually persists in spite of variations in the environment.

Distribution


United States
Parrotfeather has been introduced into Southeast Asia, Australia, New Zealand, Japan, South Africa, and North America. The earliest specimen recorded in the United States was collected April 20, 1890, from Haddonfield, New Jersey. Since then, parrotfeather has spread to 26 states including Hawaii. The current distribution is as far north as New York on the east coast, Washington on the west coast and in nearly every southern state.

MidSouth
Parrotfeather is found widely in AL, AR, LA, MS, and TN.

IPAMS Surveys:

Control Methods


Chemical Control Options for Parrotfeather
Herbicide Trade Name Application Rate Type of Chemical Effectiveness
2,4-D DMA-4 IVM 2.0 – 4.0a Selective Systemic Excellent
Aqua-Kleen 100 – 200b
Navigate 100 – 200b
Hardball 10.0 – 20.0a
Diquat Reward 8.0a Broad Spectrum Contact Good
Endothall Aquathol K 4.0 - 8.0d Broad Spectrum Contact Fair
Aquathol Super K 8.0 – 13.0e
Glyphosate Rodeo 2.0 – 5.0a Broad Spectrum Contact Good
AquaPro 2.0 – 5.0a
Imazapyr Habitat 1.0 – 3.0a Broad Spectrum Systemic Excellent
Triclopyr Renovate 3 3.0 – 8.0a Selective Systemic Fair
Rates:
a Rates expressed as quarts of product per surface acre as a surface
   broadcast application
b Rates expressed as pounds of product per surface acre, applied to
   the water
c Rates expressed as quarts of product per surface acre applied to
   the water
d Rates expressed as quarts of product per acre-foot applied to the water
e Rates expressed as pounds of product per acre-foot, applied to
   the water
Effectiveness:
Excellent = ≥ 90% control of treated plants
Good = 80% control of sprayed plants
Fair = < 80% control of sprayed plants; re-growth can be expected
Note: Use a non-ionic surfactant with broadcast applications. Use the higher rates for dense plant infestations
Biological
Currently, grass carp (Ctenopharyngodon idella) and a leaf feeding beetle (Lysathia spp.) have been evaluated for control of parrotfeather infestations. Studies show that grass carp are not effective against parrotfeather because the plant is unpalatable and not a preferred food of the fish. The leaf-feeding beetle has the potential to be an effective biological control; in South Africa it has been shown to significantly reduce emergent shoot biomass.

Chemical
Herbicides are the most common and effective means of controlling parrotfeather. Herbicide formulations that can be used to control parrotfeather include 2,4-D, diquat, glyphosate, endothall, imazapyr, and triclopyr. Glyphosate has been used as a broadcast treatment; however, it requires multiple applications per year for several years to be effective. The systemic herbicide 2,4-D as a broadcast treatment is effective in controlling parrotfeather using a broadcast treatment. Generally, only broadcast treatments have been applied to parrotfeather and little information is available on subsurface applications. Currently, no herbicide has been shown to be totally effective in controlling parrotfeather without repeated applications over time. Always read and follow label instructions when applying herbicides. Foliar applications to emergent plant portions should use 0.25% v/v of a nonionic surfactant.

Mechanical
Hand pulling and harvesting may offer temporary control on small infestations of less than one acre. Raking may not be feasible due to the rapid biomass production of parrotfeather, as dense mats are likely heavy and may damage equipment. Care must be taken to remove all plant parts (emergent shoots, submersed shoots, and roots) as well as fragments or re-growth will occur.

Physical
Drawdown may offer control in some situations, however, all water must be removed to facilitate compete drying of bottom sediments since parrotfeather will root and survive in moist soil. Dredging is generally very expensive and not feasible for most management situations.

References


Sutton, D.L. 1985. Biology and ecology of Myriophyllum aquaticum. Proceeding, 1st International Symposium on watermilfoil (Myriophyllum spicatum) and Related Haloragaceae Species. 23-24 July 1985. Vancouver, B.C. pp. 59-71.

Sutton, D.L. 1985. Parrot-feather. Aquatics 7: 6-7, 10.

Moreira, I, A. Monteira, and T. Ferreira. 1999. Biology and control of parrotfeather (Myriophyllum aquaticum) in Portugal. Ecology, Environment and Conservation 5:171-179.

More Information


Washington Department of Ecology
http://www.ecy.wa.gov/programs/wq/plants/weeds/aqua003.html
http://www.ecy.wa.gov/programs/wq/plants/weeds/parrot.html

United States Department of Agriculture: National Plant Database
http://plants.usda.gov/cgi_bin/topics.cgi?earl=plant_profile.cgi&symbol=MYAQ2

Contributing Authors


Ryan M. Wersal, Geosystems Research Institute, Mississippi State University


Contact Info


Dr. John D. Madsen
Mississippi State University
Geosystems Research Institute
Box 9652
Mississippi State, MS 39762-9652
Ph. (662)325-2428
jmadsen@gri.msstate.edu

Geosystems Research Institute
Contact: John D. Madsen, Ph.D.  •  WebMaster