Glyphosate

Glyphosate is a commonly used herbicide that is used in both aquatic and terrestrial sites. The use of glyphosate-based herbicides that are not approved for aquatic use is very unsafe and is a violation of federal and state pesticide laws. Different formulations of glyphosate are available, including isopropylamine salt of glyphosate (Rodeo®, Shore-Klear®, Aquapro®) and potassium glyphosate (Refuge®).

Aquatic Use and Considerations

Glyphosate is a systemic herbicide that moves throughout the plant tissue and works by inhibiting an important enzyme needed for multiple plant processes, including growth.

Glyphosate is effective only on plants that grow above the water. It will not be effective on plants that are submerged or have most of their foliage under water, nor will it control regrowth from seed. Glyphosate can be used to control reed canarygrass (Phalaris arundinacea), cattails (Typha spp.), purple loosestrife (Lythrum salicaria), phragmites (Phragmites australis), water hyacinth (Eichornia crassipes) and water lettuce (Pistia stratiotes).

Glyphosate needs to be applied to plants that are actively growing. Effectiveness of glyphosate treatments may be reduced if applied when plants are growing poorly, such as due to drought stress, disease, or insect damage.

Experience with species such as purple loosestrife has shown that broadcast spray treatment can be ineffective if surrounding nontarget plants are killed, since this clears an area for rapid regrowth from seeds. An alternative method of glyphosate application for small stands is effective but time-intensive: painting cut stems with glyphosate suing a wick type applicator. The herbicide will then travel from the cut stem down into the roots and kill the remaining portion of the plant. With some species, such as phragmites, it is important to remove the cut vegetation to avoid re-rootingfrom the cut material that is not treated with herbicide.

A surfactant approved for aquatic sites must be mixed with glyphosate before application. A surfactant helps the herbicide “stick” to the plant surfaces, and increases the rate of absorption. Not all surfactants are approved for use in aquatic environments and some may be toxic to aquatic organisms; the surfactant labels should be carefully read and followed.

Care must be used when applying glyphosate to prevent injury or death to desirable plants. To avoid drift, application is not recommended when winds exceed 5 mph. In addition, excessive speed or pressure during application may allow spray to drift and must be avoided.

Following treatment, plants will gradually wilt, appear yellow, and will die in approximately 2 to 7 days. It amy take up to 30 days for woody plants. Cooler or cloudy weather following treatment may delay the visible effects of treatment. Application should be avoided when heavy rain is predicted within 6 hours, because the herbicide may wash off the plants.

 Knowledge Base 

Biology and Control of Aquatic Plants 
Glyphosate Chemical Fact Sheet

Note: Products may not be registered for use in your state or locale. Check to be sure a specific use pattern is approved in your area before use. Check product labeling or your local state agency for more information. Most current product labels are available by visiting the product manufacturers website or at https://www.cdms.net