Aquacide — Aquatic Weed Control: Native Vs Invasive Phragmite

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Aquatic Weed Control: Native Vs Invasive Phragmite

Published by Jamie Markoe on November 14, 2013 0 Comments

What is a Phragmite?  Though it sounds like an exotic insect or rare incurable disease, Phragmite, is commonly known as Reed Grass.  Invasive Phragmites arrived in the 1800s from ballast on ships that arrived from Europe.  This ballast contained sediment and seeds or rhizome fragments that were frequently dumped along the shoreline. 

Phragmite is a large, coarse perennial grass that can grow up to 15 feet tall.  The leaves are 2-2.5 inches wide and 8-15 inches long that alternate on the stem.  Phragmites have a distinctive seed head with feathery plumes at the stalk end which appear mid-summer and last all winter long.

Phragmite spreads rapidly from seed and rhizomes.  Mature rhizomes can extend 6 feet below ground making physical removal difficult.  New plants grow rapidly from rhizome fragments and also from seed.  Each mature plant will produce up to 2,000 seeds each year. 

Native Phragmite provide habitat for birds, water fowl, mammals and fish.  The invasive species has such dense, stiff shoots it competes with native vegetation and stops all wildlife but a few insects from habitation.  The invasive species also limits access to lakes, rivers and recreational areas.

Native Phragmite has low stem density.  Stem is reddish-purple in spring changing to chestnut brown in the fall.  Stems are flexible and bend easily in the wind.  They are smooth with a polished shiny appearance and normally grow crooked.  Leaves drop off easily in fall.  Rhizomes have a round shape and are yellow in color.

Invasive Phragmite has high stem density.  Stem is tan through both spring and fall.  Stems are sturdy, erect and do not bend easily in the wind.  They are dull with a rough, ribbed appearance that always grow perfectly straight.  Leaves are very difficult to remove.  Rhizomes have a flattened shape and are white or light yellow in color.

Native and invasive Phragmite are both controlled with the same chemical and physical options.  There are no known biological options to date.

Glyphosate is a systemic herbicide that will kill the entire weed, root and all.  Glyphosate is virtually non toxic to mammals, birds and fish.  For best results, apply to actively growing weeds mid-summer when growth is in full bloom.  Including a liquid non-ionic surfactant will help the herbicide stick to the foliage and penetrate into the weed more readily.

Physical control is best accomplished by repeatedly cutting stems in early spring when weeds are only 12 inches high.  This will shock the weed and reduce new re-growth.  Do not cut for a minimum of 2 weeks after chemical treatment.

Phragmite often will recover 3 years after chemical treatment.  Retreatment may be needed if weeds show signs of recovery.

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