War on Weeds — Weeds are Everybody’s Problem

Phragmites (common reed)

Phragmites (Phragmites australis) is a perennial warm season grass, native to Europe. It was introduced into the U.S. as a contaminate in soil ballast (from ships). It invades wetland areas along bodies of water. As it invades it chokes out native vegetation, reduces the amount of open water, negatively impacts habitat for waterfowl, creates mosquito breeding habitat and can increase fire potential.

Phragmites has huge growth potential, it can grow up to 15 ft tall. It forms extremely dense stands with up to 60 stems per square foot. The stem is woody, hollow and has a reddish pigmentation at the base. Leaves can grow up to 20 inches long and 2 inches wide. Roots can grow up to 10 feet deep allowing them to access ground water. It spreads by rhizomes, stolons and seed. Rhizomes and stolons can grow 15-20 feet per year allowing it to spread very quickly. Seeds can be transported long distances by wind, water and animals. Its ability to spread quickly and form dense stands makes it a serious problem.

Integrated Pest Management (IPM) options

• Prevention — Learn to identify this plant. Clean equipment after leaving an infested area. Report sightings to local authorities.
• Mechanical — Mowing or pulling can be effective on small infestations, treatments will need to be repeated each year. When hand pulling remove as much of the roots as possible (it can reproduce from root fragments). Mowing should be done right before flowering occurs. Mowing at other times during the year can increase stand density. Mow below the lowest leaf (set mowing height to 6” or less).
• Cultural — Establish a healthy stand of beneficial plants that will compete with phragmites. Prescribed burning alone can thicken the stand, but when done with other control measures like chemical control or mowing it can be beneficial. Changing the water level in infested areas can help. Draining a site to dry out the soil or flooding the site so the water is 12” or deeper can reduce the vigor of phragmites.
• Chemical — Glyphosate and Imazapyr are two herbicide active ingredients that can effectively control phragmites. Both herbicides are non-selective, meaning they will also kill beneficial plants. Extreme care should be taken when using herbicides near bodies of water. Always read and follow herbicide label directions.
• If you find phragmites on your property consult with local authorities to create a control program that utilizes multiple forms of control.

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

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• Phragmites, 12-14