Hydrothol Algaecide and Herbicide

  • Highly effective granular algaecide and herbicide
  • To be applied when target algae and aquatic plants are actively growing
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Not for Sale - CA, NY

Not For Sale

in CA & NY

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Hydrothol 191 is a liquid concentrate soluble in water and is a highly effective herbicide/algaecide. Be sure to apply this product when weeds and algae are actively growing. Susceptibility of algae may vary due to subspecies, strains or environmental conditions. Dosage rates are measured in parts per million (ppm) endothall acid. Liquid product sold to commercial applicators only.

Active Ingredient: Mono(N,N-dimethylalkylamine) salt of endothall

For use on:

  • Lakes
  • Potable Water Reservoirs (Applicators must consider the unique characteristics of the treated waters to assure that endothall acid concentrations in potable drinking water do not exceed 0.1 ppm at the time of consumptiom.)
  • Ponds
  • Crop and Non-Crop Irrigtion Conveyance Systems (Ditches, Canals and Laterals)

Weeds Controlled

  • Algae - Planktonic, Filamentous, Branched
  • Fanwort
  • Brazilian Elodea
  • Elodea
  • Hydrilla
  • Hygrophila
  • Eelgrass
  • Coontail
  • Horned Pondweed
  • Milfoil
  • Sago Pondweed
  • Naiad
  • Pondweed
  • Water Stargrass
  • See label for complete listing of weeds controlled


How to Apply: Hydrothol 191 is a contact algaecide and herbicide. Apply when target algae and plants are present. Hydrothol 191 may be sprayed on te water or injected below the water surface. It may be applied as a concentrate or diluted with water depending on the equipment. Hydrothol 191 can be applied to floating algae mats as a surface application. In instances where the algae or plant(s) to be controlled is an exposed surface problem (i.e. some of the broad-leaved pond weed) coverage is important. For best results, apply the concentrate with the least amount of water compatible with the application equipment.

Quiescent or slow moving water treatments Algae control: Generally rates of 0.05 to 0.3 ppm (0.6 - 3.6 pints per ACRE/FT) are effective for the control of algae. Repeat applications when algae reappear and reach treatment levels. Dosages may be increased (from 0.3 to 3.0 ppm) where greater longevity of control is desired or to improve efficacy on species that prove difficult to control. Due to te potential for fish toxicity at higher rates, it is suggested that applications above 0.3 ppm be made only by commercial applicators as marginal or sectional treatments.
Floating Algae Mats: Apply Hydrolthol 191 when algae is actively growing. Spray Hydrothol 191 over the top of floating algae mats using a 3-5% spray solution (based on volume). Use a minimum of 0.5 GAL per surface acre with adequate water volume to asssue complete coverate.
Submerged Aquatic Plants: Apply Hydrothol 191 at 1 to 5 ppm (1.4 GAL to 6.8 GAL/ACRE FT) for control of aquatic plants. Due to potential fish toxicity, Hydrothol 191 use for submerged aquatic plant control is suggested to be made only by commercial applicators as marginal or sectional treatments. Use application rates over 1.0 ppm only on very narrow margins or in areas where some fish kill is not objectionable.

See Label for complete application instructions.


Do not apply this product in a way that will contact workers or other persons, either directly or through drift.

When used as directed, phytotoxicity is not expected on plants or crops irrigated with Hydrothol 191 treated water, however, all species and cultivars (varietites) have not been tested.

Undiluted Hydrothol 191 my be injurious ot crops, grass, ornamentals or other foliage.

Do not use Hydrothol 191 treated water for chemigation as interactions between Hydrothol 191 and other pesticides or fertilizers are not known.

Do not use Hydrothol 191 in waters containing Koi or hybrid goldfish.

Hydrothol 191 is not intended for use in small volume garden pond systems.

Fish may be killed by dosages in excess of 0.3 ppm.

Do not use Hydrolthol 191 in brackish or saltwater

Do not treat more than 10% of the area at one time with doses in excess of 1 ppm in slow moving or quiescent waters.

See Label for complete restrictions.

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