Northern Watermilfoil

[ Myriophyllum exalbescens ]

Northern Watermilfoil (Myriophyllum exalbescens) can be found in every state. Northern Watermilfoil can occur in dense patches crowding out all other growth. If the basic corrective actions are taken you should anticipate excellent control. Identify the plant, measure the control area, choose the product and dose and apply timely. It is always a good idea to keep records to assist in future control adjustments.

Note: See also Eurasian Watermilfoil (EWM) an exotic submerged that looks similar. EWM can have as many as twenty leaflet pairings. Northern Watermilfoil leaflet pairings will not exceed ten.

Northern Watermilfoil
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Northern watermilfoil is often mistaken for coontail or Eurasian watermilfoil. A large difference is it does not branch at the surface as much as Eurasian watermilfoil does. The northern variety typically has half as many leaflet pairs as Eurasian has. The leaves of the northern are rigid when removed from the water, but Eurasian leaves are limp when out of water. The northern species also forms winter buds (groups of small, dark, brittle leaves) in late fall and winter.

Q. What are the best control options?

Herbicide Application:
Hydrothol 191 Granular is a favorite, it is easy to apply and very broad spectrum. An alternative is Reward liquid herbicide equally effective and broad spectrum. Most people prefer the granular Hydrothol because of its easy to apply granular formulation.

Northern Watermilfoil plant fragments can regenerate. If you are going to physically cut or rake this plant for control we suggest limiting the control size and try to recover fragments.

Q. When is the best time to treat?

Early in the growth cycle is usually best. Water temperatures should exceed sixty degrees Fahrenheit.

Q. How do I actually apply the product(s)?

The Hydrothol 191 granules can be spread by a small Hand held spreader or can be tossed by a hand scoop. The Reward should be applied by a hand-held pump up sprayer or backpack sprayer. Reward can be applied directly from the container in small ponds or immediate dock areas.

Q. How often do I need to treat the Northern Watermilfoil?

One to two treatments per season are usually plenty.

Q. How long before I see results?

Generally within two weeks things will be cleared up.