Fluridone is an aquatic herbicide that was initially registered with the EPA in 1986. The active ingredient is 1-methyl-3-phenyl-5-3-(trifluoromethyl)phenyl|-41H|-pyridinone. Both liquid and slow-release granular formulations are available.

Aquatic Use and Considerations 

Fluridone is an herbicide that stops the plant from making a protective pigment that keeps chlorophyll from breaking down in the sun. Treated plants will turn white or pink at the growing tips after a week and will die in one to two months after treatment as it is unable to make food for itself. It is only effective if plants are growing at the time of treatment.

Fluridone is used at very low concentrations, but a very long contact time is required (45-90 days). If the fluridone is removed before the plants die, they will once again be able to produce chlorophyll and grow.

Fluridone moves rapidly through water, so it is usually applied as a whole-lake treatment to an entire waterbody or basin. There are pellet slow-release formulations that may be used as spot treatments, but the efficacy of this is undetermined. Fluridone has been applied to rivers through a drip system to maintain the concentration for the required contact time. 

Plants vary in their susceptibility to fluridone, so typically some species will not be affected even though the entire waterbody is treated.

Plants have been shown to develop resistance to repeated fluridone use, so it is recommended to rotate herbicides with different modes of action when using fluridone as a control.

Fluridone is effective at treating the invasive Eurasian watermilfoil (Myriophyllum spicatum). It also is commonly used for control of invasive hydrilla (Hydrilla verticillata) and water hyacinth (Eichhornia crassipes), neither of which are present in Wisconsin yet. Desirable native species that are usually affected at concentrations used to treat the invasives include native milfoils, coontail (Ceratophyllum demersum), naiads (Najas spp.), elodea (Elodea canadensis) and duckweeds (Lemna spp.). Lilies (Nymphaea spp. and Nuphar spp.) and bladderworts (Utricularia spp.) also can be affected.

Industrial Vegetation Management Knowledge Base 

Biology and Control of Aquatic Plants 
Fluridone 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