War on Weeds — Weeds are Everybody’s Problem

Parrotfeather milfoil

Parrotfeather milfoil (Myriophyllum aquaticum) is an aquatic perennial, native to South America. It was likely introduced as an aquarium plant that then escaped. It invades slow moving shallow bodies of water. It can form dense monocultures that have been known to dam water and cause flooding.

Parrotfeather milfoil is bright green with a soft feather-type appearance. It can be completely submerged, or it can emerge out of the water. Stems can reach up to 5 feet in length. Leaves are arranged in a whorl, pinnately compound and have a feathery appearance (20-30 divisions per leaf). Leaves that are submerged in water tend to be smaller, lighter in color and are less divided. Only female parrotfeather milfoil plants are found in North America; thus, it is not known to preform sexual reproduction. It reproduces vegetatively, through rhizomes and other plant parts that are broken off and transported.

Integrated Pest Management (IPM) options

• Prevention — Know how to identify this plant and report sightings. Never dispose of aquarium contents in surface waters. Always clean recreational equipment before transporting.
• Mechanical — Mechanical removal is usually not an effective option. Any activity that breaks plant parts increases the density of parrotfeather milfoil.
• Cultural — Physical barriers used for shade can effectively control this weed, but they also kill native species.
• Biological — In some cases North American beavers have been found to reduce parrotfeather milfoil biomass.
• Chemical — Herbicides can provide some control of parrotfeather milfoil. Be sure to use a surfactant because leaves have a waxy covering that inhibits absorption. Consult your local UI Extension office about active ingredients, rates and other important considerations. Always read and follow label directions.

Idaho is a wonderful place with awesome natural resources, landscapes, agriculture and recreational opportunities. Weeds threaten all the things that we love about Idaho. To detect, contain and control weeds in Idaho we have declared “War on Weeds.” These short articles are designed to give a brief description of each species, an explanation about why it’s a problem, insights into identification and Integrated Pest Management control options. — Justin Hatch

View or Download (pdf)

• Parrotfeather Milfoil, 5-24